Journal articles on the topic 'Considered as a Planet'
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1
Nagasawa, Makiko, Shigeru Ida, and Taisuke Bessho. "The formation of close-in planets by the slingshot model." Proceedings of the International Astronomical Union 3, S249 (October 2007): 279–84. http://dx.doi.org/10.1017/s1743921308016700.
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AbstractWe investigated the efficiency of planet scatterings in producing close-in planets by a direct inclusion of the dynamical tide effect into the simulations. We considered a system consists of three Jovian planets. Through a planet-planet scattering, one of the planets is sent into shorter orbit. If the eccentricity of the scattered planet is enough high, the tidal dissipation from the star makes the planetary orbit circular. We found that the short-period planets are formed at about 30% cases in our simulation and that Kozai mechanism plays an important role. In the Kozai mechanism, the high inclination obtained by planet-planet scattering is transformed to the eccentricity. It leads the pericenter of the innermost planet to approach the star close enough for tidal circularization. The formed close-in planets by this process have a widely spread inclination distribution. The degree of contribution of the process for the formation of close-in planets will be revealed by more observations of Rossiter-McLaughlin effects for transiting planets.
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Ji, Jianghui, and Niu Zhang. "Simulations for Terrestrial Planets Formation." Proceedings of the International Astronomical Union 5, S263 (August 2009): 45–49. http://dx.doi.org/10.1017/s1743921310001481.
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AbstractWe investigate the formation of terrestrial planets in the late stage of planetary formation using two-planet model. At that time, the protostar has formed for about 3 Myr and the gas disk has dissipated. In the model, the perturbations from Jupiter and Saturn are considered. We also consider variations of the mass of outer planet, and the initial eccentricities and inclinations of embryos and planetesimals. Our results show that, terrestrial planets are formed in 50 Myr, and the accretion rate is about 60% - 80%. In each simulation, 3 - 4 terrestrial planets are formed inside “Jupiter” with masses of 0.15 – 3.6 M⊕. In the 0.5 - 4AU, when the eccentricities of planetesimals are excited, planetesimals are able to accrete material from wide radial direction. The plenty of water material of the terrestrial planet in the Habitable Zone may be transferred from the farther places by this mechanism. Accretion may also happen a few times between two giant planets only if the outer planet has a moderate mass and the small terrestrial planet could survive at some resonances over time scale of 108 yr.
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Ipatov, Sergei I. "Collision probabilities of migrating small bodies and dust particles with planets." Proceedings of the International Astronomical Union 5, S263 (August 2009): 41–44. http://dx.doi.org/10.1017/s174392131000147x.
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AbstractProbabilities of collisions of migrating small bodies and dust particles produced by these bodies with planets were studied. Various Jupiter-family comets, Halley-type comets, long-period comets, trans-Neptunian objects, and asteroids were considered. The total probability of collisions of any considered body or particle with all planets did not exceed 0.2. The amount of water delivered from outside of Jupiter's orbit to the Earth during the formation of the giant planets could exceed the amount of water in Earth's oceans. The ratio of the mass of water delivered to a planet by Jupiter-family comets or Halley-type comets to the mass of the planet can be greater for Mars, Venus, and Mercury, than that for Earth.
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Wei, Lingfeng, Smadar Naoz, Thea Faridani, and Will M. Farr. "Relativistic Dynamical Stability Criterion of Multiplanet Systems with a Distant Companion." Astrophysical Journal 923, no. 1 (December 1, 2021): 118. http://dx.doi.org/10.3847/1538-4357/ac2c70.
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Abstract Multiplanetary systems are prevalent in our Galaxy. The long-term stability of such systems may be disrupted if a distant inclined companion excites the eccentricity and inclination of the inner planets via the eccentric Kozai–Lidov mechanism. However, the star–planet and the planet–planet interactions can help stabilize the system. In this work, we extend the previous stability criterion that only considered the companion–planet and planet–planet interactions by also accounting for short-range forces or effects, specifically, relativistic precession induced by the host star. A general analytical stability criterion is developed for planetary systems with N inner planets and a relatively distant inclined perturber by comparing precession rates of relevant dynamical effects. Furthermore, we demonstrate as examples that in systems with two and three inner planets, the analytical criterion is consistent with numerical simulations using a combination of Gauss’s averaging method and direct N-body integration. Finally, the criterion is applied to observed systems, constraining the orbital parameter space of a possible undiscovered companion. This new stability criterion extends the parameter space in which an inclined companion of multiplanet systems can inhabit.
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Cloutier, R., N. Astudillo-Defru, X. Bonfils, J. S. Jenkins, Z. Berdiñas, G. Ricker, R. Vanderspek, et al. "Characterization of the L 98-59 multi-planetary system with HARPS." Astronomy & Astrophysics 629 (September 2019): A111. http://dx.doi.org/10.1051/0004-6361/201935957.
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Aims. L 98-59 (TIC 307210830, TOI-175) is a nearby M3 dwarf around which TESS revealed three small transiting planets (0.80, 1.35, 1.57 Earth radii) in a compact configuration with orbital periods shorter than 7.5 days. Here we aim to measure the masses of the known transiting planets in this system using precise radial velocity (RV) measurements taken with the HARPS spectrograph. Methods. We considered both trained and untrained Gaussian process regression models of stellar activity, which are modeled simultaneously with the planetary signals. Our RV analysis was then supplemented with dynamical simulations to provide strong constraints on the planets’ orbital eccentricities by requiring long-term stability. Results. We measure the planet masses of the two outermost planets to be 2.42 ± 0.35 and 2.31 ± 0.46 Earth masses, which confirms the bulk terrestrial composition of the former and eludes to a significant radius fraction in an extended gaseous envelope for the latter. We are able to place an upper limit on the mass of the smallest, innermost planet of <1.01 Earth masses with 95% confidence. Our RV plus dynamical stability analysis places strong constraints on the orbital eccentricities and reveals that each planet’s orbit likely has e < 0.1. Conclusions. L 98-59 is likely a compact system of two rocky planets plus a third outer planet with a lower bulk density possibly indicative of the planet having retained a modest atmosphere. The system offers a unique laboratory for studies of planet formation, dynamical stability, and comparative atmospheric planetology as the two outer planets are attractive targets for atmospheric characterization through transmission spectroscopy. Continued RV monitoring will help refine the characterization of the innermost planet and potentially reveal additional planets in the system at wider separations.
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Khangale, Z. N., S. B. Potter, E. J. Kotze, P. A. Woudt, and H. Breytenbach. "High-speed photometry of the eclipsing polar UZ Fornacis." Astronomy & Astrophysics 621 (January 2019): A31. http://dx.doi.org/10.1051/0004-6361/201834039.
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We present 33 new mid-eclipse times spanning approximately eight years of the eclipsing polar UZ Fornacis. We have used our new observations to test the two-planet model previously proposed to explain the variations in its eclipse times measured over the past ~35 yr. We find that the proposed model does indeed follow the general trend of the new eclipse times, however, there are significant departures. In order to accommodate the new eclipse times, the two-planet model requires that one or both of the planets require highly eccentric orbits, that is, e ≥ 0.4. Such multiple planet orbits are considered to be unstable. Whilst our new observations are consistent with two cyclic variations as previously predicted, significant residuals remain. We conclude that either additional cyclic terms, possibly associated with more planets, or other mechanisms, such as the Applegate mechanism are contributing to the eclipse time variations. Further long-term monitoring is required.
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Tancredi, Gonzalo. "Physical and dynamical characteristics of icy “dwarf planets” (plutoids)." Proceedings of the International Astronomical Union 5, S263 (August 2009): 173–85. http://dx.doi.org/10.1017/s1743921310001717.
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AbstractThe geophysical and dynamical criteria introduced in the “Definition of a Planet in the Solar System” adopted by the International Astronomical Union are reviewed. The classification scheme approved by the IAU reflects dynamical and geophysical differences among planets, “dwarf planets” and “small Solar System bodies”. We present, in the form of a decision tree, the set of questions to be considered in order to classify an object as an icy “dwarf planet” (a plutoid). We find that there are 15 very probable plutoids; plus possibly 9 more, which require a reliable estimate of their sizes. Finally, the most relevant physical and dynamical characteristics of the set of icy “dwarf planets” have been reviewed; e.g. the albedo, the lightcurve amplitude, the location in the different dynamical populations, the size distributions, and the discovery rate.
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Pontoppidan, Klaus M. "Observations of planet-forming volatiles." Proceedings of the International Astronomical Union 11, A29B (August 2015): 390–94. http://dx.doi.org/10.1017/s1743921316005615.
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AbstractWater is observed to be a major constituent of planet-forming disks around young stars and its presence likely plays a major role in formation of planets and their atmospheres, including those destined to orbit in a habitable zone. Yet, the path from disks to planets is one fraught with complexity, making it difficult to derive precise theoretical predictions for planetary chemistry. Planet-forming disks are no longer considered uniform well-mixed structures; rather, they are complex worlds with many different heterogenous environments, most of which play some part in determining the composition of planetesimals and planets. Direct observations of atomic and molecular abundances on all size scales are therefore needed for understanding planet formation at a very fundamental level, and for answering the question of how chemically common the Earth is among exoplanets. In the past years, great progress has been made in observing protoplanetary chemistry, in particular in measuring the molecular composition in protoplanetary disks across the planet-forming regions from 1 to 10s of AU. We will present recent observations of water with Herschel, the VLT and Gemini in disks, and we will demonstrate how we retrieve the local abundances and radial distribution of water vapor and ice using detailed radiative transfer models. We find that most of the oxygen is likely bound in water near 1 AU in disks around solar-mass stars and that the disk surface composition at these radii is likely dominated by local gas-phase chemistry rather than by primordial material delivered from the interstellar medium. We discuss how these observations relate to complementary constraints from the solar system. We further discuss the implications for the observed composition of exoplanetary atmospheres.
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Bolmont, E., S. N. Breton, G. Tobie, C. Dumoulin, S. Mathis, and O. Grasset. "Solid tidal friction in multi-layer planets: Application to Earth, Venus, a Super Earth and the TRAPPIST-1 planets." Astronomy & Astrophysics 644 (December 2020): A165. http://dx.doi.org/10.1051/0004-6361/202038204.
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With the discovery of TRAPPIST-1 and its seven planets residing within 0.06 au, it is becoming increasingly necessary to carry out correct treatments of tidal interactions. The eccentricity, rotation, and obliquity of the planets of TRAPPIST-1 do indeed result from the tidal evolution over the lifetime of the system. Tidal interactions can also lead to tidal heating in the interior of the planets (as for Io), which may then be responsible for volcanism or surface deformation. In the majority of studies aimed at estimating the rotation of close-in planets or their tidal heating, the planets are considered as homogeneous bodies and their rheology is often taken to be a Maxwell rheology. Here, we investigate the impact of taking into account a multi-layer structure and an Andrade rheology in the way planets dissipate tidal energy as a function of the excitation frequency. We use an internal structure model, which provides the radial profile of structural and rheological quantities (such as density, shear modulus, and viscosity) to compute the tidal response of multi-layered bodies. We then compare the outcome to the dissipation of a homogeneous planet (which only take a uniform value for shear modulus and viscosity). We find that for purely rocky bodies, it is possible to approximate the response of a multi-layer planet by that of a homogeneous planet. However, using average profiles of shear modulus and viscosity to compute the homogeneous planet response leads to an overestimation of the averaged dissipation. We provide fitted values of shear modulus and viscosity that are capable of reproducing the response of various types of rocky planets. However, we find that if the planet has an icy layer, its tidal response can no longer be approximated by a homogeneous body because of the very different properties of the icy layers (in particular, their viscosity), which leads to a second dissipation peak at higher frequencies. We also compute the tidal heating profiles for the outer TRAPPIST-1 planets (e to h).
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Akinsanmi, B., S. C. C. Barros, N. C. Santos, A. C. M. Correia, P. F. L. Maxted, G. Boué, and J. Laskar. "Detectability of shape deformation in short-period exoplanets." Astronomy & Astrophysics 621 (January 2019): A117. http://dx.doi.org/10.1051/0004-6361/201834215.
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Context. Short-period planets are influenced by the extreme tidal forces of their parent stars. These forces deform the planets causing them to attain nonspherical shapes. The nonspherical shapes, modeled here as triaxial ellipsoids, can have an impact on the observed transit light-curves and the parameters derived for these planets. Aims. We investigate the detectability of tidal deformation in short-period planets from their transit light curves and the instrumental precision needed. We also aim to show how detecting planet deformation allows us to obtain an observational estimate of the second fluid Love number from the light curve, which provides valuable information about the internal structure of the planet. Methods. We adopted a model to calculate the shape of a planet due to the external potentials acting on it and used this model to modify the ellc transit tool. We used the modified ellc to generate the transit light curve for a deformed planet. Our model is parameterized by the Love number; therefore, for a given light curve we can derive the value of the Love number that best matches the observations. Results. We simulated the known cases of WASP-103b and WASP-121b which are expected to be highly deformed. Our analyses show that instrumental precision ≤50 ppm min−1 is required to reliably estimate the Love number and detect tidal deformation. This precision can be achieved for WASP-103b in ∼40 transits using the Hubble Space Telescope and in ∼300 transits using the forthcoming CHEOPS instrument. However, fewer transits will be required for short-period planets that may be found around bright stars in the TESS and PLATO survey missions. The unprecedented precisions expected from PLATO and JWST will permit the detection of shape deformation with a single transit observation. However, the effects of instrumental and astrophysical noise must be considered as they can increase the number of transits required to reach the 50 ppm min−1 detection limit. We also show that improper modeling of limb darkening can act to bury signals related to the shape of the planet, thereby leading us to infer sphericity for a deformed planet. Accurate determination of the limb darkening coefficients is therefore required to confirm planet deformation.
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Pozuelos, Francisco J., Juan C. Suárez, Gonzalo C. de Elía, Zaira M. Berdiñas, Andrea Bonfanti, Agustín Dugaro, Michaël Gillon, et al. "GJ 273: on the formation, dynamical evolution, and habitability of a planetary system hosted by an M dwarf at 3.75 parsec." Astronomy & Astrophysics 641 (September 2020): A23. http://dx.doi.org/10.1051/0004-6361/202038047.
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Context. Planets orbiting low-mass stars such as M dwarfs are now considered a cornerstone in the search for planets with the potential to harbour life. GJ 273 is a planetary system orbiting an M dwarf only 3.75 pc away, which is composed of two confirmed planets, GJ 273b and GJ 273c, and two promising candidates, GJ 273d and GJ 273e. Planet GJ 273b resides in the habitable zone. Currently, due to a lack of observed planetary transits, only the minimum masses of the planets are known: Mb sin ib = 2.89 M⊕, Mc sin ic = 1.18 M⊕, Md sin id = 10.80 M⊕, and Me sin ie = 9.30 M⊕. Despite its interesting character, the GJ 273 planetary system has been poorly studied thus far. Aims. We aim to precisely determine the physical parameters of the individual planets, in particular, to break the mass–inclination degeneracy to accurately determine the mass of the planets. Moreover, we present a thorough characterisation of planet GJ 273b in terms of its potential habitability. Methods. First, we explored the planetary formation and hydration phases of GJ 273 during the first 100 Myr. Secondly, we analysed the stability of the system by considering both the two- and four-planet configurations. We then performed a comparative analysis between GJ 273 and the Solar System and we searched for regions in GJ 273 which may harbour minor bodies in stable orbits, that is, the main asteroid belt and Kuiper belt analogues. Results. From our set of dynamical studies, we find that the four-planet configuration of the system allows us to break the mass–inclination degeneracy. From our modelling results, the masses of the planets are unveiled as: 2.89 ≤ Mb ≤ 3.03 M⊕, 1.18 ≤ Mc ≤ 1.24 M⊕, 10.80 ≤ Md ≤ 11.35 M⊕, and 9.30 ≤ Me ≤ 9.70 M⊕. These results point to a system that is likely to be composed of an Earth-mass planet, a super-Earth and two mini-Neptunes. Based on planetary formation models, we determine that GJ 273b is likely an efficient water captor while GJ 273c is probably a dry planet. We find that the system may have several stable regions where minor bodies might reside. Collectively, these results are used to offer a comprehensive discussion about the habitability of GJ 273b.
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Dash, Spandan, and Yamila Miguel. "Planet formation and disc mass dependence in a pebble-driven scenario for low-mass stars." Monthly Notices of the Royal Astronomical Society 499, no. 3 (October 2, 2020): 3510–21. http://dx.doi.org/10.1093/mnras/staa3041.
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ABSTRACT Measured disc masses seem to be too low to form the observed population of planetary systems. In this context, we develop a population synthesis code in the pebble accretion scenario, to analyse the disc mass dependence on planet formation around low-mass stars. We base our model on the analytical sequential model presented by Ormel, Liu, and Schoonenberg and analyse the populations resulting from varying initial disc mass distributions. Starting out with seeds the mass of Ceres formed by streaming instability inside the ice-line, we grow the planets using the pebble accretion process and migrate them inwards using type I migration. The next planets are formed sequentially after the previous planet crosses the ice line. We explore different initial distributions of disc masses to show the dependence of this parameter with the final planetary population. Our results show that compact close-in resonant systems can be pretty common around M dwarfs between 0.09 and 0.2 M⊙ only when the discs considered are more massive than what is being observed by sub-mm disc surveys. The minimum disc mass to form a Mars-like planet is found to be about 2 × 10−3 M⊙. Small variations in the disc mass distribution also manifest in the simulated planet distribution. The paradox of disc masses might be caused by an underestimation of the disc masses in observations, by a rapid depletion of mass in discs by planets growing within 1 million years, or by deficiencies in our current planet formation picture.
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Chanturiya, Soso M., Raguli I. Inasaridze, Rolan I. Kiladze, and Omar M. Kurtanidze. "Astrometric Programmes of the Abastumani Observatory." International Astronomical Union Colloquium 148 (1995): 241–44. http://dx.doi.org/10.1017/s0252921100021989.
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AbstractAstrometric investigations undertaken with the 70 cm meniscus and 40 cm double astrograph telescopes are considered. We describe the determination of accurate positions for minor planets, giant-planet satellites, late-type stars, extragalactic radio-sources, optically discovered quasars and compact extragalactic objects in the Second Byurakan Survey.
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Danilov, V. I. "GELIOGEOPHYSICAL PHENOMENA INDUCED BY EXTERNAL GRAVITATIONAL FORCES." Вестник Пермского университета. Геология 21, no. 3 (2022): 247–63. http://dx.doi.org/10.17072/psu.geol.21.3.247.
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It is shown that an external gravitational action onto the planet core leads to the generation of its magnetic field. The natural phenomena as earthquakes, orogeny, oceanic currents, tides, time and solar day sudden changes, periodic solar activity, which can be easily explained with proposed mechanism of planets interaction are considered. Clear relationship of planets magnetic fields, their forms and value from solar activity, magnetic and gravitational fields measurements, oceanic level monitoring, as well as natural processes observation data may be accepted as evidence. Analysis of all the data leads to the unique conclusion about the influence of Earth’s core movement to many processes occurred and measured on the planet surface. Proposed approach allows integrating many separate processes to the single hole.
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Mercer, Anthony, and Dimitris Stamatellos. "Planet formation around M dwarfs via disc instability." Astronomy & Astrophysics 633 (January 2020): A116. http://dx.doi.org/10.1051/0004-6361/201936954.
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Context. Around 30 per cent of the observed exoplanets that orbit M dwarf stars are gas giants that are more massive than Jupiter. These planets are prime candidates for formation by disc instability. Aims. We want to determine the conditions for disc fragmentation around M dwarfs and the properties of the planets that are formed by disc instability. Methods. We performed hydrodynamic simulations of M dwarf protostellar discs in order to determine the minimum disc mass required for gravitational fragmentation to occur. Different stellar masses, disc radii, and metallicities were considered. The mass of each protostellar disc was steadily increased until the disc fragmented and a protoplanet was formed. Results. We find that a disc-to-star mass ratio between ~0.3 and ~0.6 is required for fragmentation to happen. The minimum mass at which a disc fragment increases with the stellar mass and the disc size. Metallicity does not significantly affect the minimum disc fragmentation mass but high metallicity may suppress fragmentation. Protoplanets form quickly (within a few thousand years) at distances around ~50 AU from the host star, and they are initially very hot; their centres have temperatures similar to the ones expected at the accretion shocks around planets formed by core accretion (up to 12 000 K). The final properties of these planets (e.g. mass and orbital radius) are determined through long-term disc-planet or planet–planet interactions. Conclusions. Disc instability is a plausible way to form gas giant planets around M dwarfs provided that discs have at least 30% the mass of their host stars during the initial stages of their formation. Future observations of massive M dwarf discs or planets around very young M dwarfs are required to establish the importance of disc instability for planet formation around low-mass stars.
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Ziglina, I. N., and O. Yu Schmidt. "Stochastic Behaviour of Planetary Orbits During the Accumulation Process." International Astronomical Union Colloquium 132 (1993): 137–48. http://dx.doi.org/10.1017/s025292110006601x.
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AbstractThe evolution of orbital elements of a growing planet during the accumulation process is considered. The planetary orbit undergoes perturbations because of random encounters and collisions with bodies of its accretion zone and also because of gravitational interaction with an already formed massive planet (“Jupiter”). The mass and velocity distributions of the swarm bodies are assumed to be given time-dependent functions. The Fokker-Planck equation describing the behaviour of the distribution function of orbital elements of the growing planet is worked out and solved. The present mean values of the eccentricities and inclinations of orbits of the terrestrial planets can be explained in the case of their accumulation from a single swarm of bodies with mean mass ~ 10−2 M⊕ and with mean eccentricities and inclinations ~ 0.2.
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Dupuy, Trent J., Adam L. Kraus, Kaitlin M. Kratter, Aaron C. Rizzuto, Andrew W. Mann, Daniel Huber, and Michael J. Ireland. "Orbital architectures of planet-hosting binaries – II. Low mutual inclinations between planetary and stellar orbits." Monthly Notices of the Royal Astronomical Society 512, no. 1 (February 4, 2022): 648–60. http://dx.doi.org/10.1093/mnras/stac306.
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ABSTRACT Planet formation is often considered in the context of one circumstellar disc around one star. Yet, stellar binary systems are ubiquitous, and thus a substantial fraction of all potential planets must form and evolve in more complex, dynamical environments. We present the results of a 5 yr astrometric monitoring campaign studying 45 binary star systems that host Kepler planet candidates. The planet-forming environments in these systems would have literally been shaped by the binary orbits that persist to the present day. Crucially, the mutual inclinations of star–planet orbits can only be addressed by a statistical sample. We describe in detail our sample selection and Keck/NIRC2 laser guide star adaptive optics observations collected from 2012 to 2017. We measure orbital arcs, with a typical accuracy of ∼0.1 mas yr−1, that test whether the binary orbits tend to be aligned with the edge-on transiting planet orbits. We rule out randomly distributed binary orbits at 4.7σ, and we show that low mutual inclinations are required to explain the observed orbital arcs. If the stellar orbits have a field binary-like eccentricity distribution, then the best match to our observed orbital arcs is a distribution of mutual inclinations ranging from 0° to 30°. We discuss the implications of such widespread planet–binary alignment in the theoretical context of planet formation and circumstellar disc evolution.
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Fujita, Naho, Yasunori Hori, and Takanori Sasaki. "Orbital Evolution of Close-in Super-Earths Driven by Atmospheric Escape." Astrophysical Journal 928, no. 2 (March 30, 2022): 105. http://dx.doi.org/10.3847/1538-4357/ac558c.
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Abstract The increasing number of super-Earths close to their host stars have revealed a scarcity of close-in small planets with 1.5–2.0 R ⊕ in the radius distribution of Kepler planets. The atmospheric escape of super-Earths by photoevaporation can explain the origin of the observed “radius gap.” Many theoretical studies have considered the in situ mass loss of a close-in planet. Planets that undergo atmospheric escape, however, move outward due to the change in the orbital angular momentum of their star–planet systems. In this study, we calculate the orbital evolution of an evaporating super-Earth with a H2/He atmosphere around FGKM-type stars under stellar X-ray and extreme-UV irradiation (XUV). The rate of increase in the orbital radius of an evaporating planet is approximately proportional to that of the atmospheric mass loss during a high stellar XUV phase. We show that super-Earths with a rocky core of ≲10 M ⊕ and a H2/He atmosphere at ≲0.03–0.1 au (≲0.01–0.03 au) around G-type stars (M-type stars) are prone to outward migration driven by photoevaporation. Although the changes in the orbits of the planets would be small, they would rearrange the orbital configurations of compact, multiplanet systems, such as the TRAPPIST-1 system. We also find that the radius gap and the so-called “Neptune desert” in the observed population of close-in planets around FGK-type stars still appear in our simulations. On the other hand, the observed planet population around M-type stars can be reproduced only by a high stellar XUV luminosity model.
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Downey, Brynna G., and Alessandro Morbidelli. "An attempt to constrain Planet Nine’s orbit and position via resonant confinement of distant TNOs." Monthly Notices of the Royal Astronomical Society 494, no. 2 (April 14, 2020): 2045–52. http://dx.doi.org/10.1093/mnras/staa790.
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ABSTRACT We considered four TNOs on elongated orbits with small semimajor axis uncertainties: Sedna, 2004 VN112, 2012 VP113, and 2000 CR105. We found two sets of simultaneous near commensurabilities for these objects with a putative Planet Nine that are compatible with the current uncertainties in the objects’ orbital periods. We conducted a large number of numerical simulations of quasi-coplanar simulations (i.e. inclinations of Planet Nine and TNOs set to zero but not the giant planets) to find which values of Planet Nine’s mean anomaly and longitude of perihelion could put these objects in stable mean motion resonance (MMR) librations. We found no cases of simultaneous stable librations for multiple TNOs for more than 800 My, with most librations lasting much shorter than this time-scale. The objects 2004 VN112 and 2000 CR105 are the most unstable. Being in an MMR is not a strict requirement for long-term survival in 3D simulations, so our result cannot be used to refute Planet Nine’s existence. Nevertheless, it casts doubt and shows that theoretical attempts to constrain the position of the planet on the sky are not possible.
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Millholland, Sarah C., Matthias Y. He, and Jon K. Zink. "Edge-of-the-Multis: Evidence for a Transition in the Outer Architectures of Compact Multiplanet Systems." Astronomical Journal 164, no. 2 (August 1, 2022): 72. http://dx.doi.org/10.3847/1538-3881/ac7c67.
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Abstract Although the architectures of compact multiple-planet systems are well characterized, there has been little examination of their “outer edges,” or the locations of their outermost planets. Here we present evidence that the observed high-multiplicity Kepler systems truncate at smaller orbital periods than can be explained by geometric and detection biases alone. To show this, we considered the existence of hypothetical planets orbiting beyond the observed transiting planets with properties dictated by the “peas-in-a-pod” patterns of intrasystem radius and period ratio uniformity. We evaluated the detectability of these hypothetical planets using (1) a novel approach for estimating the mutual inclination dispersion of multitransiting systems based on transit chord length ratios, and (2) a model of transit probability and detection efficiency that accounts for the impacts of planet multiplicity on completeness. Under the assumption that the “peas-in-a-pod” patterns continue to larger orbital separations than observed, we find that ≳35% of Kepler compact multis should possess additional detected planets beyond the known planets, constituting a ∼7σ discrepancy with the lack of such detections. These results indicate that the outer (∼100–300 days) regions of compact multis experience a truncation (i.e., an “edge-of-the-multis”) or a significant breakdown of the “peas-in-a-pod” patterns, in the form of systematically smaller radii or larger period ratios. We outline future observations that can distinguish these possibilities, and we discuss implications for planet formation theories.
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Khodachenko, Maxim L., H. Lammer, H. I. M. Lichtenegger, J. M. Grießmeier, M. Holmström, and A. Ekenbäck. "The role of intrinsic magnetic fields in planetary evolution and habitability: the planetary protection aspect." Proceedings of the International Astronomical Union 4, S259 (November 2008): 283–94. http://dx.doi.org/10.1017/s1743921309030622.
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AbstractThe widely used definition of a habitable zone (HZ) for planets as a circumstellar area, where the star's luminosity is sufficiently intense to maintain liquid water at the surface of a planet, is shown to be too simplified. The role of a host star's activity and the intrinsic magnetic field of a planet with respect to their influence on mass loss processes of close-in gas giants and a definition of a HZ for the terrestrial-type exoplanets are discussed. The stellar X-ray/EUV radiation and the stellar wind result in ionization, heating, chemical modification, and slow erosion of the planetary upper atmospheres throughout their lifetime. The closer the planet is to the star, the more efficient are these processes, and therefore, the more important becomes the magnetic protection of a planet as a potential habitat. Different ways for planetary magnetic dipole moment estimation, based on existing magnetic dynamo scaling laws as well as on the recent measurements of hot atomic hydrogen clouds around close-in ‘Hot Jupiters’ are considered, and the predictions of these estimations are compared to each other.
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Dalba, Paul A., Stephen R. Kane, Diana Dragomir, Steven Villanueva, Karen A. Collins, Thomas Lee Jacobs, Daryll M. LaCourse, et al. "The TESS-Keck Survey. VIII. Confirmation of a Transiting Giant Planet on an Eccentric 261 Day Orbit with the Automated Planet Finder Telescope*." Astronomical Journal 163, no. 2 (January 13, 2022): 61. http://dx.doi.org/10.3847/1538-3881/ac415b.
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Abstract We report the discovery of TOI-2180 b, a 2.8 M J giant planet orbiting a slightly evolved G5 host star. This planet transited only once in Cycle 2 of the primary Transiting Exoplanet Survey Satellite (TESS) mission. Citizen scientists identified the 24 hr single-transit event shortly after the data were released, allowing a Doppler monitoring campaign with the Automated Planet Finder telescope at Lick Observatory to begin promptly. The radial velocity observations refined the orbital period of TOI-2180 b to be 260.8 ± 0.6 days, revealed an orbital eccentricity of 0.368 ± 0.007, and discovered long-term acceleration from a more distant massive companion. We conducted ground-based photometry from 14 sites spread around the globe in an attempt to detect another transit. Although we did not make a clear transit detection, the nondetections improved the precision of the orbital period. We predict that TESS will likely detect another transit of TOI-2180 b in Sector 48 of its extended mission. We use giant planet structure models to retrieve the bulk heavy-element content of TOI-2180 b. When considered alongside other giant planets with orbital periods over 100 days, we find tentative evidence that the correlation between planet mass and metal enrichment relative to stellar is dependent on orbital properties. Single-transit discoveries like TOI-2180 b highlight the exciting potential of the TESS mission to find planets with long orbital periods and low irradiation fluxes despite the selection biases associated with the transit method.
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Walsh, Kevin J. "Forming terrestrial planets and delivering water." Proceedings of the International Astronomical Union 11, A29B (August 2015): 427–30. http://dx.doi.org/10.1017/s174392131600572x.
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AbstractBuilding models capable of successfully matching the Terrestrial Planet's basic orbital and physical properties has proven difficult. Meanwhile, improved estimates of the nature of water-rich material accreted by the Earth, along with the timing of its delivery, have added even more constraints for models to match. While the outer Asteroid Belt seemingly provides a source for water-rich planetesimals, models that delivered enough of them to the still-forming Terrestrial Planets typically failed on other basic constraints - such as the mass of Mars.Recent models of Terrestrial Planet Formation have explored how the gas-driven migration of the Giant Planets can solve long-standing issues with the Earth/Mars size ratio. This model is forced to reproduce the orbital and taxonomic distribution of bodies in the Asteroid Belt from a much wider range of semimajor axis than previously considered. In doing so, it also provides a mechanism to feed planetesimals from between and beyond the Giant Planet formation region to the still-forming Terrestrial Planets.
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De Vet, S. J., and W. Van Westrenen. "Introduction: Planetary geosciences, the Dutch contribution to the exploration of our solar system." Netherlands Journal of Geosciences - Geologie en Mijnbouw 95, no. 2 (March 28, 2016): 109–12. http://dx.doi.org/10.1017/njg.2016.8.
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Planetary geoscience was effectively born when Christiaan Huygens took his first look at planet Mars on Friday 28 November 1659. As one of the leading scientists of his time, Huygens was known for constructing his own telescopes to observe stars, planets and nebulae whenever the clear and spacious skies above the Netherlands allowed. Huygens observed the planet Mars during the heydays of its 1659 opposition. On the night of 28 November he succeeded in sketching the first albedo feature on a different planet in our solar system. The roughly triangular dark-coloured patch was originally christened the Hourglass Sea, suggesting it to be an area of open water. Perhaps the landscape surrounding him in the Netherlands prompted Huygens to interpret the newly discovered feature as a wet area on the planet's surface. The attribution of traits to an albedo feature on another planet based on terrestrial landscapes may well be considered as the first-ever attempt at ‘comparative planetology’. The albedo feature can still be recognised at the surface of Mars today as Syrtis Major. Any modest amateur telescope can provide a view superior to that of Huygens’, allowing the observation of the very first geological feature ever identified on another rocky planet.
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Jones, Barrie W., P. Nick Sleep, and David R. Underwood. "Which exoplanetary systems could harbour habitable planets?" International Journal of Astrobiology 5, no. 3 (July 2006): 251–59. http://dx.doi.org/10.1017/s1473550406003132.
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Habitable planets are likely to be broadly Earth-like in composition, mass and size. Masses are likely to be within a factor of a few Earth masses – we call such planets Earth-mass planets. It is important to find such planets. Currently, we do not have sufficiently sensitive techniques to detect planets with such small masses, except in rare circumstances. It is thus necessary to model the known exoplanetary systems to see whether Earth-mass planets could be present. In particular, we need to establish whether such planets could be present in the classical habitable zone (HZ), or whether the giant planets that we know to be present have gravitationally ejected Earth-mass planets or prevented their formation. We have answered this question by applying computer models to the 152 exoplanetary systems known as of 18 April 2006 that are sufficiently well characterized for our analysis. For systems in which there is a giant planet interior to the HZ, which must have got there by migration, there are two cases considered: first, the case when the migration of the giant planet across the HZ has not ruled out the existence of an Earth-mass planet in the HZ; second, the case where it has. In the former case we have found that 60% of the 152 systems offer safe havens to Earth-mass planets across greater than 20% of the HZ width. We regard such systems as being habitable today. We have also estimated whether habitability is possible for 1000 Myr into the past (provided that this period post-dates the heavy bombardment of planets in the HZ). Of the 143 systems that are susceptible to this second analysis, we find that about 50% offer habitability sustained over 1000 Myr. If giant planets interior to the HZ rule Earth-mass planets, then 60% and 50% fall to 7% in both cases.
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Sheppard, Scott S., and David C. Jewitt. "The Abundant Irregular Satellites of the Giant Planets." Highlights of Astronomy 13 (2005): 898–900. http://dx.doi.org/10.1017/s1539299600017469.
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AbstractIrregular satellites have eccentric orbits that can be highly inclined or even retrograde relative to the equatorial planes of their planets. These objects cannot have formed by circumplanetary accretion as did the regular satellites which follow un-inclined, nearly circular, pro-grade orbits. Instead, they are likely products of early capture from heliocentric orbit. The study of the irregular satellites provides a unique window on processes operating in the young solar system. Recent discoveries around Jupiter (45 new satellites), Saturn (13), Uranus (9), and Neptune (5) have almost increased the number of known irregular satellites by a factor of ten and suggest that the gas and ice giant planets all have fairly similar irregular satellite systems. Dynamical groupings were most likely produced by collisional shattering of precursor objects after capture by their planets. Jupiter is considered as a case of special interest. Its proximity allows us to probe the fainter, smaller irregular satellites to obtain large population statistics in order to address the questions of planet formation and capture.
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Shibata, Sho, Ravit Helled, and Masahiro Ikoma. "The origin of the high metallicity of close-in giant exoplanets." Astronomy & Astrophysics 633 (January 2020): A33. http://dx.doi.org/10.1051/0004-6361/201936700.
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Context. Recent studies suggest that in comparison to their host star, many giant exoplanets are highly enriched with heavy elements and can contain several tens of Earth masses of heavy elements or more. Such enrichment is considered to have been delivered by the accretion of planetesimals in late formation stages. Previous dynamical simulations, however, have shown that planets cannot accrete such high masses of heavy elements through “in situ” planetesimal accretion. Aims. We investigate whether a giant planet migrating inward can capture planetesimals efficiently enough to significantly increase its metallicity. Methods. We performed orbital integrations of a migrating giant planet and planetesimals in a protoplanetary gas disc to infer the planetesimal mass that is accreted by the planet. Results. We find that the two shepherding processes of mean motion resonance trapping and aerodynamic gas drag inhibit the planetesimal capture of a migrating planet. However, the amplified libration allows the highly-excited planetesimals in the resonances to escape from the resonance trap and to be accreted by the planet. Consequently, we show that a migrating giant planet captures planetesimals with total mass of several tens of Earth masses if the planet forms at a few tens of AU in a relatively massive disc. We also find that planetesimal capture occurs efficiently in a limited range of semi-major axis and that the total captured planetesimal mass increases with increasing migration distances. Our results have important implications for understanding the relation between giant planet metallicity and mass, as we suggest that it reflects the formation location of the planet – or more precisely, the location where runaway gas accretion occurred. We also suggest the observed metal-rich close-in Jupiters migrated to their present locations from afar, where they had initially formed.
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Molaie, Moslem, Samira Deylaghian, Giovanni Iarriccio, Farhad S. Samani, Antonio Zippo, and Francesco Pellicano. "Planet Load-Sharing and Phasing." Machines 10, no. 8 (July 30, 2022): 634. http://dx.doi.org/10.3390/machines10080634.
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This paper presents an analysis of the scientific literature devoted to the problem of load sharing and phasing in planetary gearboxes. The wide range of research topics demonstrates the technical challenges of understanding planetary load-sharing and planet phasing. This review includes studies having the goal of developing models for load sharing and exploring the positive or negative effects of different parameters such as phasing on the load distribution among planets. Practical aspects are also considered, for example, the effects of some errors that are unavoidable during manufacturing or working conditions, e.g., misalignments or position errors. Methods for improving the load-sharing characteristics, e.g., flexible ring or floating components, are discussed as well.
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Van Flandern, Tom. "The challenge of the exploded planet hypothesis." International Journal of Astrobiology 6, no. 3 (June 20, 2007): 185–97. http://dx.doi.org/10.1017/s1473550407003758.
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AbstractThe hypothesis of the explosion of a number of planets and moons of our Solar System during its 4.6-billion-year history is in excellent accord with all known observational constraints, even without adjustable parameters or ad hoc helper hypotheses. Many of its boldest predictions have been fulfilled. In most instances, these predictions were judged highly unlikely by the current standard models. Moreover, in several cases, the entire exploded planet model was at risk of being falsified if the predictions failed. The successful predictions include: (1) satellites of asteroids; (2) satellites of comets; (3) salt water in meteorites; (4) ‘roll marks’ leading to boulders on asteroids; (5) the time and peak rate of the 1999 Leonid meteor storm; (6) explosion signatures for asteroids; (7) the strongly spiked energy parameter for new comets; (8) the distribution of black material on slowly rotating airless bodies; (9) splitting velocities of comets; (10) the asteroid-like nature of Deep Impact target Comet Tempel 1; and (11) the presence of high-formation-temperature minerals in the Stardust comet dust sample return. In physics and astronomy, hypotheses are either falsified if their predictions fail, or proved to be of value if they succeed. By all existing evidence, the exploded planet hypothesis has proved far more useful than the half-dozen or so hypotheses it would replace. Among the many important corollaries are these. (a) Perhaps as many as six former planets of our Solar System have exploded over its 4.6-billion-year history. (b) In particular, Mars is not an original planet, but a former moon of an exploded planet. (c) As a major player in Solar System evolution, the exploded planet scenario must be considered as a likely propagation vehicle for the spread of biogenic organisms. We conclude with a brief mention of three possible planetary explosion mechanisms.
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Baluev, Roman V. "Several problems of exoplanetary orbits determination from radial velocity observations." Proceedings of the International Astronomical Union 3, S249 (October 2007): 101–10. http://dx.doi.org/10.1017/s1743921308016463.
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AbstractExisting algorithms of analysis of radial velocity time series are improved for the purposes of extrasolar planets detection and characterizing. Three important effects are considered: the poorly known radial velocity jitter, periodic systematic errors, and statistical bias due to non-linearity of models. Mathematical tools to account for these effects are developed and applied to a number of real planetary systems. In particular, it is shown that two outer planets of HD37124 are likely trapped in the 2/1 resonance. The dwarf star GJ876 may host an extra, Neptune-mass, planet which is in resonance with two giant planets in this system.
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Eistrup, Christian, Catherine Walsh, and Ewine F. van Dishoeck. "Chemical evolution in planet-forming regions. Impact on volatile abundances and C/O ratios of planet-building material." Proceedings of the International Astronomical Union 13, S332 (March 2017): 69–72. http://dx.doi.org/10.1017/s1743921317009802.
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AbstractConnecting the observed composition of exoplanets to their formation sites often involves comparing the atmospheric C/O ratio to a disk midplane model with a fixed chemical composition. In this scenario chemistry during the planet formation era is not considered. However, kinetic chemical evolution during the lifetime of the gaseous disk can change the relative abundances of volatile species, thus altering the C/O ratios of planetary building blocks. In our chemical evolition models we utilize a large network of gas-phase, grain-surface and gas-grain interaction reactions, thus providing a comprehensive treatment of chemistry. The results show that, if sufficient ionisation is present, then chemistry does alter the C/O ratios of gas and ice during the epoch of planet(esimal) formation. This modifies the picture of C/O ratios in disk midplanes defined simply by volatile ice lines in a midplane of fixed chemical composition. Chemical evolution thus needs to be addressed when predicting the makeup of planets and their atmospheres.
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Nakagawa, Yoshitsugu. "Possible in situ Formation of Close Giant Planets in a Passive Quiescent Nebula." Symposium - International Astronomical Union 202 (2004): 285–90. http://dx.doi.org/10.1017/s007418090021807x.
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Formation of giant planets along the standard model is considered in the innermost region of protoplanetary nebulae where turbulence has already decayed. Preference of quiescent nebulae is discussed. It is shown that if dust material enough to form a core with about ten times Earth mass and the corresponding amount of gas exist in the innermost region, a giant planet with mass somewhat larger than our Jupiter can form there.
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Kiang, Nancy Y. "Looking for life elsewhere: Photosynthesis and astrobiology." Biochemist 36, no. 6 (December 1, 2014): 24–30. http://dx.doi.org/10.1042/bio03606024.
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Photosynthesis produces signs of life we can see from space: the absorbance spectrum of surface photosynthetic pigments and, with oxygenic photosynthesis, atmospheric oxygen. Since the first discovery of a planet in another solar system in 1989, there has been an explosion in the detection of exoplanets (over 1849 as of 7 November 2014) and we are getting ever closer to finding that Goldilocks planet that might harbour life. With telescope observations of these planets, oxygenic photosynthesis has been considered our most robust target ‘biosignature’ that would not appear on a lifeless planet. Since anoxygenic photosynthetic organisms do not produce unambiguously biogenic gases, there is interest in their pigments serving as spectral indicators of life. But will they look the same as on Earth, can we distinguish them from the abiotic, and what will dominate on another planet? Examples from Earth provide us with the potential to extrapolate some rules for photosynthesis to predict its signature on another planet, but there are yet things we must answer about life here to improve our confidence. In particular, given the combination of the available stellar spectrum and molecular constraints on photon energy use, can we predict the pigment spectral features that will dominate, which reductant will match, and what biogenic gases would result? We take clues from the diversity of anoxygenic photosynthetic metabolisms and three very recent examples of oxygenic photosynthesis utilizing other reaction centre (RC) chlorophylls in addition to chlorophyll a (Chl a).
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Gomes, R. S. "Some Aspects of Particle's Dynamics." Symposium - International Astronomical Union 152 (1992): 349–54. http://dx.doi.org/10.1017/s0074180900091361.
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Some features of the dynamics of particles affected by drag, in the field of the Sun and planets, are presented here. In particular mean motion and secular resonances are investigated. When dust particles are considered as a whole in the zodiacal cloud, a simple secular theory can explain much of its geometry. Dynamics of particles near an inner planet is mostly dispersive, but an average behavior can be deduced from some analytical and numerical considerations.
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Mihailidis, Athanassios, Anastasios Moisiadis, and Andreas Psarros. "Impact of backlash, manufacturing deviations and friction on the load sharing factor of planetary gear systems." MATEC Web of Conferences 287 (2019): 01003. http://dx.doi.org/10.1051/matecconf/201928701003.
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Techniques and software tools, which were recently introduced by the authors, allowed for effi-cient automatic generation of 3D gear flanks and selective meshing of the gears of a simple planetary gear system with backlash and manufacturing imperfections. Friction of the meshing gear flanks was neglected. First results were promising and showed that even in geometrically perfect planetary gear systems the torque distribution is not uniform. It was further verified that pitch errors have a strong impact on the load distri-bution and that a self-aligning sun gear significantly enhances the torque distribution among the planets. In the current study, the procedure mentioned above is enhanced in several aspects. First, the tooth friction is considered. The friction coefficient is assumed constant along the path of contact; however different values for the sun-planet and planet-ring gear mesh may be given to account for the different contact conditions. Second, deviations are generated between given limits in a stochastic way. This feature significantly reduces the time needed to setup a model. Third, the entire analysis procedure is further automated by extensively employing Python scripting, enabling the solution of successive snapshots in much shorter time. Besides the torque distribution among the planets, the mesh load factor Kγ and the deformation of the teeth, the planet bearing load is also shown.
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Sicardy, Bruno. "Small Bodies Around Other Stars." Symposium - International Astronomical Union 160 (1994): 429–42. http://dx.doi.org/10.1017/s0074180900046696.
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We briefly review recent advances in the observation and study of planetary bodies in extra-solar systems. We summarize in particular the main physical properties of the β-Pictoris dust disk, and the status of new disk observations. Theoretical implications of infalling discrete bodies are considered, in particular, the existence of possible perturbing planet(s) causing this influx. Such planets could spectacularly disturb circumstellar dust disks, thus revealing themselves in spite of their intrinsic faintness as mere point sources. Finally, we describe the recent possible discovery of at least two planets around a pulsar. This underlines the potential existence of planets in rather exotic circumstances.
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Sucerquia, Mario, Vanesa Ramírez, Jaime A. Alvarado-Montes, and Jorge I. Zuluaga. "Can close-in giant exoplanets preserve detectable moons?" Monthly Notices of the Royal Astronomical Society 492, no. 3 (December 18, 2019): 3499–508. http://dx.doi.org/10.1093/mnras/stz3548.
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ABSTRACT Exoplanet discoveries have motivated numerous efforts to find unseen populations of exomoons, yet they have been unsuccessful. A plausible explanation is that most discovered planets are located on close-in orbits, which would make their moons prone to tidal evolution and orbital detachment. In recent models of tidally driven migration of exomoons, evolving planets might prevent what was considered their most plausible fate (i.e. colliding against their host planet), favouring scenarios where moons are pushed away and reach what we define as the satellite tidal orbital parking distance ($a_{\rm \mathrm{stop}}$), which is often within the critical limit for unstable orbits and depends mainly on the system’s initial conditions: mass ratio, semimajor axes, and rotational rates. Using semi-analytical calculations and numerical simulations, we calculate $a_{\rm \mathrm{stop}}$ for different initial system parameters and constrain the transit detectability of exomoons around close-in planets. We found that systems with Mm/Mp ≥ 10−4, which are less likely to form, are also stable and detectable with present facilities (e.g. Kepler and TESS) through their direct and secondary effects in planet + moon transit, as they are massive, oversized, and migrate slowly. In contrast, systems with lower moon-to-planet mass ratios are ephemeral and hardly detectable. Moreover, any detection, confirmation, and full characterization would require both the short cadence capabilities of TESS and high photometric sensitivity of ground-based observatories. Finally, despite the shortage of discovered long-period planets in currently available data bases, the tidal migration model adopted in this work supports the idea that they are more likely to host the first detectable exomoon.
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Ogihara, Masahiro, Eiichiro Kokubo, Takeru K. Suzuki, Alessandro Morbidelli, and Aurélien Crida. "Effects of global gas flows on type I migration." Astronomy & Astrophysics 608 (December 2017): A74. http://dx.doi.org/10.1051/0004-6361/201730777.
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Context. Magnetically-driven disk winds would alter the surface density slope of gas in the inner region of a protoplanetary disk (r ≲ 1 au). This in turn affects planet formation. Recently, the effect of disk wind torque has been considered with the suggestion that it would carve out the surface density of the disk from inside and would induce global gas flows (wind-driven accretion). Aims. We aim to investigate effects of global gas flows on type I migration and also examine planet formation. Methods. A simplified approach was taken to address this issue, and N-body simulations with isolation-mass planets were also performed. Results. In previous studies, the effect of gas flow induced by turbulence-driven accretion has been taken into account for its desaturation effect of the corotation torque. If more rapid gas flows (e.g., wind-driven accretion) are considered, the desaturation effect can be modified. In MRI-inactive disks, in which the wind-driven accretion dominates the disk evolution, the gas flow at the midplane plays an important role. If this flow is fast, the corotation torque is efficiently desaturated. Then, the fact that the surface density slope can be positive in the inner region due to the wind torque can generate an outward migration region extended to super-Earth mass planets. In this case, we observe that no planets fall onto the central star in N-body simulations with migration forces imposed to reproduce such migration pattern. We also see that super-Earth mass planets can undergo outward migration. Conclusions. Relatively rapid gas flows affects type I migration and thus the formation of close-in planets.
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Melnikov, A. V. "Secular dynamics of a number of planetary systems from the TESS catalog." Publications of the Pulkovo Observatory 227 (December 2022): 1–10. http://dx.doi.org/10.31725/0367-7966-2022-227-9.
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A study was made of the stability of the orbital dynamics of a number of planets discovered based on data analysis from the TESS orbital observatory. For twelve circumstellar planetary systems, characteristic estimates of the Lyapunov time (the time of the predictable dynamics) are obtained and, based on them, conclusions about the character of stability are drawn. The secular orbital dynamics of the ten considered planetary systems is stable. For planet TOI-905 the calculated Lyapunov time is small (less than 3000 years), which indicates a possible inaccuracy in determining the parameters of this planetary system. A detailed analysis of the stability of the secular dynamics of two circumbinary planets - TOI-1338 and TIC 172900988, was carried out. For these planetary systems, stability diagrams are constructed and analyzed, and estimates of the Lyapunov times are obtained. On the stability diagrams of the planet TOI-1338 and TIC 172900988 are located in regions of stable dynamics with large Lyapunov times (more than 7000) years, which confirms the reliability of the parameters of these planetary systems established from the analysis of observations.
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Makalkin, A. B., I. N. Ziglina, and M. E. Artyushkova. "Topical problems in the theory of planet formation: formation of planetesimals." Физика Земли, no. 1 (March 27, 2019): 104–21. http://dx.doi.org/10.31857/s0002-333720191104-121.
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The development of the Earth’s and planets formation theory over 70 years is considered with a special focus on the history of development of this theory at the Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences (IPE RAS) where this direction of research was founded by Otto Schmidt. The state of the art of the theory is outlined. In particular, the planetesimals formation problem currently belonging to the key unsolved issues in the theory of planet formation is discussed. Recent results of the studies aimed at solving this problem at IPE RAS are presented.
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Carrión-González, Ó., A. García Muñoz, J. Cabrera, Sz Csizmadia, N. C. Santos, and H. Rauer. "Directly imaged exoplanets in reflected starlight: the importance of knowing the planet radius." Astronomy & Astrophysics 640 (August 2020): A136. http://dx.doi.org/10.1051/0004-6361/202038101.
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Context. The direct imaging of exoplanets in reflected starlight will represent a major advance in the study of cold and temperate exoplanet atmospheres. Understanding how basic planet and atmospheric properties may affect the measured spectra is key to their interpretation. Aims. We have investigated the information content in reflected-starlight spectra of exoplanets. We apply our analysis to Barnard’s Star b candidate super-Earth, for which we assume a radius 0.6 times that of Neptune, an atmosphere dominated by H2–He, and a CH4 volume mixing ratio of 5 × 10−3. The main conclusions of our study are however planet-independent. Methods. We set up a model of the exoplanet described by seven parameters including its radius, atmospheric methane abundance, and basic properties of a cloud layer. We generated synthetic spectra at zero phase (full disc illumination) from 500 to 900 nm and a spectral resolution R ~ 125–225. We simulated a measured spectrum with a simplified, wavelength-independent noise model at a signal-to-noise ratio of 10. With a retrieval methodology based on Markov chain Monte Carlo sampling, we analysed which planet and atmosphere parameters can be inferred from the measured spectrum and the theoretical correlations amongst them. We considered limiting cases in which the planet radius is either known or completely unknown, and intermediate cases in which the planet radius is partly constrained. Results. If the planet radius is known, we can generally discriminate between cloud-free and cloudy atmospheres, and constrain the methane abundance to within two orders of magnitude. If the planet radius is unknown, new correlations between model parameters occur and the accuracy of the retrievals decreases. Without a radius determination, it is challenging to discern whether the planet has clouds, and the estimates on methane abundance degrade. However, we find the planet radius is constrained to within a factor of two for all the cases explored. Having a priori information on the planet radius, even if approximate, helps improve the retrievals. Conclusions. Reflected-starlight measurements will open a new avenue for characterizing long-period exoplanets, a population that remains poorly studied. For this task to be complete, direct-imaging observations should be accompanied by other techniques. We urge exoplanet detection efforts to extend the population of long-period planets with mass and radius determinations.
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Gunaydin, Gizem, Gamze Duvan, and Eren Ozceylan. "An Integrated Approach of Multi-Criteria Decision Making to Determine the Most Habitable Planet." HighTech and Innovation Journal 3, no. 2 (February 19, 2022): 151–61. http://dx.doi.org/10.28991/hij-2022-03-02-04.
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Every planet in the universe has its own characteristics. These features make the planets different among themselves. For this reason, all the different properties of the planets must be evaluated at the same time when determining habitable planets. This situation requires a multi-criteria decision making (MCDM) approach. In this study, a list of habitable planets (nine planets and the Moon) has been considered. Seventeen different criteria such as mass, gravity, diameter, density, escape velocity, rotation time, day of length, distance from the sun, perihelion, aphelion, orbital period, orbital velocity, orbital inclination, orbital eccentricity, obliquity to orbit, mean temperature, and number of satellites are taken into account. The weights of criteria are determined with DEMATEL (The Decision Making Trial and Evaluation Laboratory) by analyzing the interactions among criteria. Orbital inclination is the criterion with the highest weight, and the criterion with the lowest weight is the number of satellites. After weighting the criteria with DEMATEL, VIKOR (VIseKriterijumska Optimizacija I Kompromisno Resenje) and TOPSIS (Technique for Order Preference to Similarity to Ideal Solution) approaches are used to rank the planets. According to the TOPSIS, Earth is ranked first, Venus ranked second and Mercury ranked third in the order of the most habitable planets. According to the VIKOR method, Earth is ranked first, Mars is ranked second, and Mercury is ranked third in the order of the most habitable planets. Finally, the same calculations are considered with equal weights and the results are discussed. Doi: 10.28991/HIJ-2022-03-02-04 Full Text: PDF
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Huang, Qi Lin, Yong Wang, Zhi Pu Huo, Jun Gang Wang, and Ruo Yu Sheng. "Free Torsional Vibration Characteristics of a Closed-Form Planetary Gear Set." Applied Mechanics and Materials 300-301 (February 2013): 1042–47. http://dx.doi.org/10.4028/www.scientific.net/amm.300-301.1042.
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A purely torsional dynamic model of closed-form planetary gear set is developed to investigate its natural frequency and free vibration modes. The closed-form planetary gear set considered consists of two-stage planetary gear connected by high-speed carrier and ring gear. Three identical planet gears are equally spaced in each stage. Based on the precondition, the natural modes are classified into three types of vibration modes: overall modes，high-speed planet mode and low-speed planet mode
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Escalera-Briceño, Alejandro, Manuel Ángeles-Villa, and Alejandro Palafox-Muñoz. "¿Por qué se debe considerar al marxismo ecológico en la era del capitaloceno?/ Why should ecological Marxism be considered in the era of the capitalocene?" Letras Verdes. Revista Latinoamericana de Estudios Socioambientales, no. 23 (February 22, 2018): 69–90. http://dx.doi.org/10.17141/letrasverdes.23.2018.2867.
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Este artículo pretende adentrarse en el debate marxismo/ecología, para subrayar la importancia de renovar las categorías marxistas del materialismo histórico y dialéctico para el análisis profundo de la era del capitaloceno. Se inicia con un bosquejo de las principales corrientes no marxistas que explican la relación del ser humano con la naturaleza a través de enfoques “híbridos”, como la economía ecológica (en sus tres vertientes) y la ecología política. En el ánimo de proponerlo como alternativa robusta a estas conceptualizaciones, se realiza enseguida un apretado recorrido cronológico del marxismo ecológico para examinar algunos de los principales textos constitutivos, desde el propio Marx hasta el actual debate entre Bellamy Foster y Moore. Se consigna que en el capitaloceno, portador de enormes amenazas al planeta, a la especie humana y al propio capitalismo, los debates actuales en el seno del marxismo ecológico ofrecen una provechosa lectura del crisol de contradicciones del capitalismo avanzado.
Abstract
The objective of this paper is to make inroads into de debates within ecological Marxism in order to underscore the importance of looking at the Marxist categories of historical materialism and dialectics in the light of the ongoing era of the Capitalocene. We began with a summary of recent developments in non-Marxist disciplines that deal with the human / nature interface through “hybrid approaches, such as ecological economics and political ecology. With a view of forwarding a proposal for ecological Marxism as a viable and robust alternative, we then mobilize into play several quotations from Marx on the subject, in order to lead us into the current debates between, mainly, Bellamy Foster and Jason Moore. We suggest that in the Capitalocene, purveyor great threats to the planet, humanity and capitalism itself, those debates can offer very worthwhile readings of the contradictions of advanced capitalism.
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A’Hearn, Michael F. "Pluto: A Planet or a Trans-Neptunian Object?" Highlights of Astronomy 12 (2002): 201–4. http://dx.doi.org/10.1017/s1539299600013277.
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AbstractThe purposes of classification and taxonomy are reviewed. Using examples from fields ranging from paleontology to planetology, I argue that non-exclusive classifications, which allow Pluto to be considered both a planet and a TNO, provide the most desirable approach to progress in our science.
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Turrini, D., A. Zinzi, and J. A. Belinchon. "Normalized angular momentum deficit: a tool for comparing the violence of the dynamical histories of planetary systems." Astronomy & Astrophysics 636 (April 2020): A53. http://dx.doi.org/10.1051/0004-6361/201936301.
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Context. Population studies of the orbital characteristics of exoplanets in multi-planet systems have highlighted the existence of an anticorrelation between the average orbital eccentricity of planets and the number of planets of their host system, that is, its multiplicity. This effect was proposed to reflect the varying levels of violence in the dynamical evolution of planetary systems. Aims. Previous work suggested that the relative violence of the dynamical evolution of planetary systems with similar orbital architectures can be compared through the computation of their angular momentum deficit (AMD). We investigated the possibility of using a more general metric to perform analogous comparisons between planetary systems with different orbital architectures. Methods. We considered a modified version of the AMD, the normalized angular momentum deficit (NAMD), and used it to study a sample of 99 multi-planet systems containing both the currently best-characterized extrasolar systems and the solar system, that is, planetary systems with both compact and wide orbital architectures. Results. We verified that the NAMD allows us to compare the violence of the dynamical histories of multi-planet systems with different orbital architectures. We identified an anticorrelation between the NAMD and the multiplicity of the planetary systems, of which the previously observed eccentricity–multiplicity anticorrelation is a reflection. Conclusions. Our results seem to indicate that phases of dynamical instabilities and chaotic evolution are not uncommon among planetary systems. They also suggest that the efficiency of the planetary formation process in producing high-multiplicity systems is likely to be higher than that suggested by their currently known population.
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Langlois, M., A. Pohl, A. M. Lagrange, A. L. Maire, D. Mesa, A. Boccaletti, R. Gratton, et al. "First scattered light detection of a nearly edge-on transition disk around the T Tauri star RY Lupi." Astronomy & Astrophysics 614 (June 2018): A88. http://dx.doi.org/10.1051/0004-6361/201731624.
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Context. Transition disks are considered sites of ongoing planet formation, and their dust and gas distributions could be signposts of embedded planets. The transition disk around the T Tauri star RY Lup has an inner dust cavity and displays a strong silicate emission feature. Aims. Using high-resolution imaging we study the disk geometry, including non-axisymmetric features, and its surface dust grain, to gain a better understanding of the disk evolutionary process. Moreover, we search for companion candidates, possibly connected to the disk. Methods. We obtained high-contrast and high angular resolution data in the near-infrared with the VLT/SPHERE extreme adaptive optics instrument whose goal is to study the planet formation by detecting and characterizing these planets and their formation environments through direct imaging. We performed polarimetric imaging of the RY Lup disk with IRDIS (at 1.6 μm), and obtained intensity images with the IRDIS dual-band imaging camera simultaneously with the IFS spectro-imager (0.9–1.3 μm). Results. We resolved for the first time the scattered light from the nearly edge-on circumstellar disk around RY Lup, at projected separations in the 100 au range. The shape of the disk and its sharp features are clearly detectable at wavelengths ranging from 0.9 to 1.6 μm. We show that the observed morphology can be interpreted as spiral arms in the disk. This interpretation is supported by in-depth numerical simulations. We also demonstrate that these features can be produced by one planet interacting with the disk. We also detect several point sources which are classified as probable background objects.
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Burger, C., Á. Bazsó, and C. M. Schäfer. "Realistic collisional water transport during terrestrial planet formation." Astronomy & Astrophysics 634 (February 2020): A76. http://dx.doi.org/10.1051/0004-6361/201936366.
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Context. According to the latest theoretical and isotopic evidence, Earth’s water content originates mainly from today’s asteroid belt region, or at least from the same precursor material. This suggests that water was transported inwards to Earth, and to similar planets in their habitable zone, via (giant) collisions of planetary embryos and planetesimals during the chaotic final phase of planet formation. Aims. In current dynamical simulations water delivery to terrestrial planets is still studied almost exclusively by assuming oversimplified perfect merging, even though water and other volatiles are particularly prone to collisional transfer and loss. To close this gap we have developed a computational framework to model collisional water transport by direct combination of long-term N-body computations with dedicated 3D smooth particle hydrodynamics (SPH) collision simulations of differentiated, self-gravitating bodies for each event. Methods. Post-collision water inventories are traced self-consistently in the further dynamical evolution, in accretionary or erosive as well as hit-and-run encounters with two large surviving bodies, where besides collisional losses, water transfer between the encountering bodies has to be considered. This hybrid approach enables us for the first time to trace the full dynamical and collisional evolution of a system of approximately 200 bodies throughout the whole late-stage accretion phase (several hundred Myr). As a first application we choose a Solar System-like architecture with already formed giant planets on either circular or eccentric orbits and a debris disk spanning the whole terrestrial planet region (0.5–4 au). Results. Including realistic collision treatment leads to considerably different results than simple perfect merging, with lower mass planets and water inventories reduced regularly by a factor of two or more. Due to a combination of collisional losses and a considerably lengthened accretion phase, final water content, especially with giant planets on circular orbits, is strongly reduced to more Earth-like values, and closer to results with eccentric giant planets. Water delivery to potentially habitable planets is dominated by very few decisive collisions, mostly with embryo-sized or larger objects and only rarely with smaller bodies, at least if embryos have formed throughout the whole disk initially. The high frequency of hit-and-run collisions and the differences to predominantly accretionary encounters, such as generally low water (and mass) transfer efficiencies, are a crucial part of water delivery, and of system-wide evolution in general.
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Pinilla-Alonso, Noemi. "Icy Dwarf Planets: Colored Popsicles in the Outer Solar System." Proceedings of the International Astronomical Union 11, A29A (August 2015): 241–46. http://dx.doi.org/10.1017/s1743921316002970.
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AbstractWe update the list of candidates to be considered by the IAU as dwarf planets using the criterium suggested by Tancredi & Favre (2008). We add here the information collected in the last 10 years (mostly the sizes and albedos by the herschel hey program TNOs Are Cool). We compare the physical characteristics of these candidates with the physical characteristics of the rest of the TNOs. Our goal is to study if there are common physical properties among the candidates that enable the identification of a dwarf planet.
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Perger, M., I. Ribas, G. Anglada-Escudé, J. C. Morales, P. J. Amado, J. A. Caballero, A. Quirrenbach, et al. "The CARMENES search for exoplanets around M dwarfs." Astronomy & Astrophysics 649 (May 2021): L12. http://dx.doi.org/10.1051/0004-6361/202140786.
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Context. The interaction between Earth-like exoplanets and the magnetic field of low-mass host stars are considered to produce weak emission signals at radio frequencies. A study using LOFAR data announced the detection of radio emission from the mid M-type dwarf GJ 1151 that could potentially arise from a close-in terrestrial planet. Recently, the presence of a 2.5-M⊕ planet orbiting GJ 1151 with a 2-day period has been claimed using 69 radial velocities (RVs) from the HARPS-N and HPF instruments. Aims. We have obtained 70 new high-precision RV measurements in the framework of the CARMENES M-dwarf survey and use these data to confirm the presence of the claimed planet and to place limits on possible planetary companions in the GJ 1151 system. Methods. We analysed the periodicities present in the combined RV data sets from all three instruments and calculated the detection limits for potential planets in short-period orbits. Results. We cannot confirm the recently announced candidate planet and conclude that the 2-day signal in the HARPS-N and HPF data sets is most probably produced by a long-term RV variability, possibly arising from an outer planetary companion that has yet to be constrained. We calculate a 99.9% significance detection limit of 1.50 m s−1 in the RV semi-amplitude, which places upper limits of 0.7 M⊕ and 1.2 M⊕ on the minimum masses of potential exoplanets with orbital periods of 1 and 5 days, respectively.