A classification system is presented for characterizing the composition of planetary bodies. From mass-radius and mass-density relationships, planets may be broadly grouped into five composition classes identified as: Gas Giant, Rock-Ice Giant, gas-rich Terrestrial, Rock Terrestrial, and Rock-Ice Terrestrial based upon the mass fractions of H-He gas, rock, and ice. For each of these broad composition classes, specific bulk composition classes are defined and characterized with Solar System analog names. The classification system allows for both general and detailed characterization of exoplanets based upon planetary mass-radius-composition models and provides rationale for distinguishing gas-rich super-Earths from mini-Neptunes.
Small bodies, the unaccreted leftovers of planetary formation, are often mistaken for the leftovers of planetary science in the sense that they are everything else after the planets and their satellites (or sometimes just their regular satellites) are accounted for. This mistaken view elides the great diversity of compositions, histories, and present-day conditions and processes found in the small bodies, and the interdisciplinary nature of their study. Understanding small bodies is critical to planetary science as a field, and we urge planetary scientists and our decision makers to continue t…
Galactic cosmic rays undergo complex nuclear interactions with nuclei within planetary bodies that have little to no atmosphere. Radiation transport simulations are a key tool used in understanding the neutron and gamma-ray albedo coming from these interactions and tracing these signals back to geochemical composition of the target. We study the validity of the code Geant4 for simulating such interactions by comparing simulation results to data from the Apollo 17 Lunar Neutron Probe Experiment. Different assumptions regarding the physics are explored to demonstrate how these impact the Geant4 …
Planetary bodies such as asteroids, comets, and planetary moons are high-value science targets as they hold important information about the formation and evolution of our solar system. However, due to their low-gravity, variable sizes and shapes, dedicated orbiting spacecraft missions around these target bodies is difficult. Therefore, many planetary bodies are observed during flyby encounters, and consequently, the mapping coverage of the target body is limited. In this work, we propose the use of a spacecraft swarm to provide complete surface maps of a planetary body during a close encounter…
The compositions of diverse planetary bodies are of fundamental interest to planetary science, providing clues to the formation and evolutionary history of the target bodies and the Solar system as a whole. Utilizing the X-ray fluorescence unique to each atomic element, X-ray imaging spectroscopy is a powerful diagnostic tool of the chemical and mineralogical compositions of diverse planetary bodies. Until now the mass and volume of focusing X-ray optics have been too large for resource-limited in-situ missions, so near-target X-ray observations of planetary bodies have been limited to simple …
Whether it is fluorescence emission from asteroids and moons, solar wind charge exchange from comets, exospheric escape from Mars, pion reactions on Venus, sprite lighting on Saturn, or the Io plasma torus in the Jovian magnetosphere, the Solar System is surprisingly rich and diverse in X-ray emitting objects. The compositions of diverse planetary bodies are of fundamental interest to planetary science, providing clues to the formation and evolutionary history of the target bodies and the solar system as a whole. X-ray fluorescence (XRF) lines, triggered either by solar X-rays or energetic ion…
Energetic Neutral Atom (ENA) imaging has been noticed as a powerful tool for remote sensing the plasma-neutral interaction in space. Particularly, the technique is used for investigation of space plasma near planetary bodies. Hear we provide a short review of recent low-energy ENA observations (up to ~1 keV) near Mars, Venus and the Moon.
Most major planetary bodies in the solar system rotate in the same direction as their orbital motion: their spin is prograde. Theoretical studies to explain the direction as well as the magnitude of the spin vector have had mixed success. When the accreting building blocks are $\sim$ km-size planetesimals -- as predicted by the classical model -- the accretion process is so symmetric that it cancels out prograde with retrograde spin contributions, rendering the net spin minute. For this reason, the currently-favored model for the origin of planetary rotation is the giant impact model, in which…
The search for extrasolar planets in the past decades has shown that planets abound in the Solar neighborhood. While we are still missing an Earth twin, the forthcoming space missions and ground-based instrumentation are already driven to achieve this goal. But, in order to fully understand the conditions for life appearing in the Solar System, we still miss some pieces of the planetary system jigsaw puzzle, namely a deeper understanding of the minor bodies. Trojans, moons, and comets are tracers of the formation and evolution processes of planetary systems. These missing pieces are also criti…
Planetary radars have obtained unique science measurements about solar system bodies and they have provided orbit determinations allowing spacecraft to be navigated throughout the solar system. Notable results have been on Venus, Earth's "twin," and small bodies, which are the constituents of the Sun's debris disk. Together, these results have served as "ground truth" from the solar system for studies of extrasolar planets. The Nation's planetary radar infrastructure, indeed the world's planetary radar infrastructure, is based on astronomical and deep space telecommunications infrastructure, n…
We present a new technique to perform passive bistatic subsurface radar probes on airless planetary bodies. This technique uses the naturally occurring radio impulses generated when high-energy cosmic rays impact the body's surface. As in traditional radar sounding, the downward-beamed radio emission from each individual cosmic ray impact will reflect off subsurface dielectric contrasts and propagate back up to the surface to be detected. We refer to this technique as Askaryan radar after the fundamental physics process, the Askaryan effect, that produces this radio emission. This technique ca…
Spin-orbit coupling of planetary systems plays an important role in the dynamics and habitability of planets. However, symplectic integrators that can accurately simulate not only how orbit affects spin but also how spin affects orbit have not been constructed for general systems. Thus, we develop symplectic Lie-group integrators to simulate systems consisting gravitationally interacting rigid bodies. A user friendly package (GRIT \url{https://github.com/GRIT-RBSim/GRIT}) is provided and external forcings such as tidal interactions are also included. As a demonstration, this package is applied…
Laboratory experiments show that dusty bodies in a gaseous environment eject dust particles if they are illuminated. We find that even more intense dust eruptions occur when the light source is turned off. We attribute this to a compression of gas by thermal creep in response to the changing temperature gradients in the top dust layers. The effect is studied at a light flux of 13 kW/(m*m) and 1 mbar ambient pressure. The effect is applicable to protoplanetary disks and Mars. In the inner part of protoplanetary disks, planetesimals can be eroded especially at the terminator of a rotating body. …
The recently adopted Ariel ESA mission will measure the atmospheric composition of a large number of exoplanets. This information will then be used to better constrain planetary bulk compositions. While the connection between the composition of a planetary atmosphere and the bulk interior is still being investigated, the combination of the atmospheric composition with the measured mass and radius of exoplanets will push the field of exoplanet characterisation to the next level, and provide new insights of the nature of planets in our galaxy. In this white paper, we outline the ongoing activiti…
We have developed an online radiative-transfer suite (https://psg.gsfc.nasa.gov) applicable to a broad range of planetary objects (e.g., planets, moons, comets, asteroids, TNOs, KBOs, exoplanets). The Planetary Spectrum Generator (PSG) can synthesize planetary spectra (atmospheres and surfaces) for a broad range of wavelengths (UV/Vis/near-IR/IR/far-IR/THz/sub-mm/Radio) from any observatory (e.g., JWST, ALMA, Keck, SOFIA), any orbiter (e.g., ExoMars, Juno), or any lander (e.g., MSL). This is achieved by combining several state-of-the-art radiative transfer models, spectroscopic databases and p…
The aim of the chapter is to summarize our understanding of the compositional distribution across the different reservoirs of small bodies (main belt asteroids, giant planet trojans, irregular satellites of the giant planets, TNOs, comets). We then use this information to i) discuss current dynamical models (Nice and Grand Tack models), ii) mention possible caveats in these models if any, and iii) draw a preliminary version of the primordial compositional gradient across the solar system before planetary migrations occured. Note that the composition of both planetary satellites (the regular on…
Topography is the expression of both internal and external processes of a planetary body. Thus hypsometry (the study of topography) is a way to decipher the dynamic of a planet. For that purpose, the statistics of height and slopes may be described by different tools, at local and global scale. We propose here to use the multifractal approach to describe fields of topography. This theory both encompass height and slopes and other statistical moment of the field, tacking into account the scale invariance. Contrary to the widely used fractal formalism, multifractal is able to describe the interm…
Planets grow via the collisional accretion of small bodies in a protoplanetary disk. Such small bodies feel strong gas drag and their orbits are significantly affected by the gas flow and atmospheric structure around the planet. We investigate the gas flow in the protoplanetary disk perturbed by the gravity of the planet by three-dimensional hydrodynamic simulation. We then calculate the orbital evolutions of particles in the gas structure obtained from the hydrodynamic simulation. Based on the orbital calculations, we obtain the collision rate between the planet and centimeter to kilometer si…
One of the longstanding unsolved problems of planet formation is how solid bodies of a few decimeters in size can "stick" to form large planetesimals. This is known as the "meter size barrier". In recent years it has become increasingly clear that some form of "particle trapping" must have played a role in overcoming the meter size barrier. Particles can be trapped in long-lived local pressure maxima, such as those in anticyclonic vortices, zonal flows or those believed to occur near ice lines or at dead zone boundaries. Such pressure traps are the ideal sites for the formation of planetesimal…
Comets and small planetesimals are believed to contain primordial building blocks in the form of millimeter to centimeter sized pebbles. One of the viable growing mechanisms to form these small bodies is through the streaming instability (SI) in which pebbles cluster and gravitationally collapse towards a planetesimal or comet in the presence of gas drag. However, most SI simulations are global and lack the resolution to follow the final collapse stage of a pebble cloud within its Hill radius. We aim to track the collapse of a gravitationally bound pebble cloud subject to mutual collisions and…
The scattering of small bodies by planets is an important dynamical process in planetary systems. We present an analytical model to describe this process using the simplifying assumption that each particle's dynamics is dominated by a single planet at a time. As such the scattering process can be considered as a series of three body problems during each of which the Tisserand parameter with respect to the relevant planet is conserved. This constrains the orbital parameter space into which a particle can be scattered. Such arguments have previously been applied to the process by which comets ar…
We present a GPU-accelerated numerical integrator specifically optimized for stability calculations of small bodies in planetary systems. Specifically, the integrator is designed for cases when large numbers of test particles (tens or hundreds of thousands) need to be followed for long durations (millions of orbits) to assess the orbital stability of their initially "close-encounter free" orbits. The GLISSE (Gpu Long-term Integrator for Solar System Evolution) code implements several optimizations to achieve a roughly factor of 100 speed increase over running the same code on a CPU. We explain…
We make use of a new hybrid method to simulate the long-term, multiple-orbit disc formation through tidal disruptions of rocky bodies by white dwarfs, at high-resolution and realistic semi-major axis. We perform the largest-yet suite of simulations for dwarf and terrestrial planets, spanning four orders of magnitude in mass, various pericentre distances and semi-major axes between 3 AU and 150 AU. This large phase space of tidal disruption conditions has not been accessible through the use of previous codes. We analyse the statistical and structural properties of the emerging debris discs, as …
The loss and gain of volatile elements during planet formation is key for setting their subsequent climate, geodynamics, and habitability. Two broad regimes of volatile element transport in and out of planetary building blocks have been identified: that occurring when the nebula is still present, and that occurring after it has dissipated. Evidence for volatile element loss in planetary bodies after the dissipation of the solar nebula is found in the high Mn to Na abundance ratio of Mars, the Moon, and many of the solar system's minor bodies. This volatile loss is expected to occur when the bo…
Super-Earths, a class of planetary bodies with masses ranging from a few Earth-masses to slightly smaller than Uranus, have recently found a special place in the exoplanetary science. Being slightly larger than a typical terrestrial planet, super-Earths may have physical and dynamical characteristics similar to those of Earth whereas unlike terrestrial planets, they are relatively easier to detect. Because of their sizes, super-Earths can maintain moderate atmospheres and possibly dynamic interiors with plate tectonics. They also seem to be more common around low-mass stars where the habitable…
Airless planetary bodies are covered by a dusty layer called regolith. The grain size of the regolith determines the temperature and the mechanical strength of the surface layers. Thus, knowledge of the grain size of planetary regolith helps to prepare future landing and/or sample-return missions. In this work, we present a method to determine the grain size of planetary regolith by using remote measurements of the thermal inertia. We found that small bodies in the Solar System (diameter less than ~100 km) are covered by relatively coarse regolith grains with typical particle sizes in the mill…
Here it is shown how to find the interior structure of a variety of rock-and-iron planetary bodies by using the rock density and some aspects of the core density as known for the Earth and using a convection principle for the iron-rich core. Convection minimizes both the density and temperature gradients inside the core fluid. This is achieved if the density of the core fluid is close to pure iron melting density at the core-mantle boundary, and the density has the smallest value possible for iron-rich melt at the inner core boundary. The critical iron densities for both pure iron and iron wit…
Two distinct thermal evolutionary pathways of irregular shaped small planetesimals in the early solar system have been studied. We have taken a case study of two S-type asteroids; (243) Ida and (951) Gaspra, on the basis of their precise physical dimensions accessed by the Philip Stooke small body 3-D shape models of the NASA Planetary Data System. The 3- D shape models for the two asteroids are based on the Galileo spacecraft fly-by mission. Based on our novel thermal evolutionary code for the precise shape of the asteroids we found that the small planetary bodies that accreted within the ini…
We present the results of a search for additional bodies in the GJ 1132 system through two methods: photometric transits and transit timing variations of the known planet. We collected 21 transit observations of GJ 1132b with the MEarth-South array since 2015. We obtained 100 near-continuous hours of observations with the $Spitzer$ Space Telescope, including two transits of GJ 1132b and spanning 60\% of the orbital phase of the maximum period at which bodies coplanar with GJ 1132b would pass in front of the star. We exclude transits of additional Mars-sized bodies, such as a second planet or a…
We present the results of planet formation N-body simulations based on a comprehensive physical model that includes planetary mass growth through mutual embryo collisions and planetesimal/boulder accretion, viscous disc evolution, planetary migration and gas accretion onto planetary cores. The main aim of this study is to determine which set of model parameters leads to the formation of planetary systems that are similar to the compact low mass multi-planet systems that have been discovered by radial velocity surveys and the Kepler mission. We vary the initial disc mass, solids-to-gas ratio an…
A planetary instability occurring at time $<100$ My after formation of the giant planets in our solar system can be responsible for some characteristics of the inner solar system. However, the actual influence of the instability on the terrestrial planet formation is not well understood. The simulations of terrestrial planet formation are very CPU-expensive, and this limits the exploration of different instability scenarios. To include the effects of the giant planets instability in the simulations of terrestrial planets formation in a feasible way, we approach the problem in two steps. First,…
In planetary nebulae, abundances of oxygen and other heavy elements derived from optical recombination lines are systematically higher than those derived from collisionally excited lines. We investigate the hypothesis that the destruction of solid bodies may produce pockets of cool, high-metallicity gas that could explain these abundance discrepancies. Under the assumption of maximally efficient radiative ablation, we derive two fundamental constraints that the solid bodies must satisfy in order that their evaporation during the planetary nebula phase should generate a high enough gas phase me…
Water content and the internal evolution of terrestrial planets and icy bodies are closely linked. The distribution of water in planetary systems is controlled by the temperature structure in the protoplanetary disk and dynamics and migration of planetesimals and planetary embryos. This results in the formation of planetesimals and planetary embryos with a great variety of compositions, water contents and degrees of oxidation. The internal evolution and especially the formation time of planetesimals relative to the timescale of radiogenic heating by short-lived 26Al decay may govern the amount…
The majority of stars both host planetary systems and evolve into a white dwarf (WD). To understand their post-main-sequence (PMS) planetary system evolution, we present a search for transiting/eclipsing planets and other Substellar Bodies (SBs) around WDs using a sample of 1148 WDs observed by K2. Using transit injections, we estimate the completeness of our search. We place constraints on the occurrence of planets and substellar bodies around white dwarfs as a function of planet radius and orbital period. For short-period ($P < 40$ days) small objects, from asteroid-sized to $1.5 \ R_{\oplus…
We re-process the Atacama Large Millimeter/Submillimeter Array (ALMA) long-baseline science verification data taken toward HL Tauri. As shown by the previous work, we confirm that the high spatial resolution (~ 0."019, corresponding to ~ 2.7 AU) dust continuum images at λ= 0.87, 1.3, and 2.9 mm exhibit a multiple ring-like gap structure in the circumstellar disk. Assuming that the observed gaps are opened up by currently forming, unseen bodies, we estimate the mass of such hypothetical bodies based on following two approaches; the Hill radius analysis and a more elaborated approach developed f…
This concept article discusses the challenges of identifying planetary-origin meteorites of non-igneous composition, primarily of sedimentary origin, distinct from SNC meteorites. The paper reviews evidence on putative sedimentary-origin meteorites and potential parent bodies for sedimentary meteorites. Authors conclude that the list of candidate parent bodies for sedimentary meteorites includes, but is not limited by the Earth, Mars, Enceladus, Ganymede, Europa, and hypothetical planets that could exist between orbits of Mars and Jupiter in the past. Authors argue that extraterrestrial origin…
Solid body tides provide key information on the interior structure, evolution, and origin of the planetary bodies. Our Solar system harbours a very diverse population of planetary bodies, including those composed of rock, ice, gas, or a mixture of all. While a rich arsenal of geophysical methods has been developed over several years to infer knowledge about the interior of the Earth, the inventory of tools to investigate the interiors of other Solar-system bodies remains limited. With seismic data only available for the Earth, the Moon, and Mars, geodetic measurements, including the observatio…
Intense tidal heating within Io produces active volcanism on the surface, and its internal structure has long been a subject of debate. A recent reanalysis of the Galileo magnetometer data suggested the presence of a high melt fraction layer with $>$50~km thickness in the subsurface region of Io. Whether this layer is a ``magmatic sponge'' with interconnected solid or a rheologically liquid ``magma ocean'' would alter the distribution of tidal heating and would also influence the interpretation of various observations. To this end, we explore the steady state of a magmatic sponge and estimate …
Determining the distribution and spectral signature of volatile ices and organics exposed on icy body surfaces can provide crucial clues for deciphering how the outer solar system formed and evolved. Over the past few decades, ground- and space-based telescope observations have probed the compositions of a wide range of icy objects with primordial and processed surfaces, revealing the presence of numerous volatile ices and organic residues. Although these telescope observations have advanced our understanding of icy bodies beyond Saturn, the sensitivity and spatial resolution of collected data…
Spitzer IRAC observations of 15 metal-polluted white dwarfs reveal infrared excesses in the spectral energy distributions of HE 0110-5630, GD 61, and HE 1349-2305. All three of these stars have helium-dominated atmospheres, and their infrared emissions are consistent with warm dust produced by the tidal destruction of (minor) planetary bodies. This study brings the number of metal-polluted, helium and hydrogen atmosphere white dwarfs surveyed with IRAC to 53 and 38 respectively. It also nearly doubles the number of metal-polluted helium-rich white dwarfs found to have closely orbiting dust by …
Core Accretion, the most widely accepted scenario for planet formation, postulates existence of km-sized solid bodies, called planetesimals, arranged in a razor-thin disc in the earliest phases of planet formation. In the Tidal Downsizing hypothesis, an alternative scenario for formation of planets, grain growth, sedimentation and formation of planetary cores occur inside dense and massive gas clumps formed in the outer cold disc by gravitational instability. As a clump migrates inward, tidal forces of the star remove all or most of the gas from the clump, downsizing it to a planetary mass bod…
Direct gravitational simulations of n-body systems have a time complexity O(n^2), which gets computationally expensive as the number of bodies increases. Distributing this workload to multiple cores significantly speeds up the computation and is the fundamental principle behind parallel computing. This project simulates (evolves) our solar system for the next 1000 years (from 2015 to 3015) on the BlueCrystal supercomputer. The gravitational bodies (planets, moons, asteroids) were successfully simulated, and the initial states (mass, position and velocity vectors) of the solar system objects we…
In their model for the origin of the parent bodies of iron meteorites, Bottke et al proposed differentiated planetesimals that were formed in the region of 1-2 AU during the first 1.5 Myr, as the parent bodies, and suggested that these objects and their fragments were scattered into the asteroid belt as a result of interactions with planetary embryos. Although viable, this model does not include the effect of a giant planet that might have existed or been growing in the outer regions. We present the results of a concept study where we have examined the effect of a planetary body in the orbit o…
Employing the finite element and computational fluid dynamics methods, we have determined the conditions for the fragmentation of space bodies or preservation of their integrity when they penetrate into the Earth's atmosphere. The origin of forces contributing to the fragmentation of space iron bodies during the passage through the dense layers of the planetary atmosphere has been studied. It was shown that the irregular shape of the surface can produce transverse aerodynamic forces capable of causing deformation stress in the body exceeding the tensile strength threshold of iron.
The melt productivity of a differentiated planet's mantle is primarily controlled by its iron content, which is itself approximated by the planet's core mass fraction (CMF). Here we show that estimates of an exo-planet's CMF allows robust predictions of the thickness, composition and mineralogy of the derivative crust. These predicted crustal compositions allow constraints to be placed on volatile cycling between surface and the deep planetary interior, with implications for the evolution of habitable planetary surfaces. Planets with large, terrestrial-like, CMFs ($\geq$0.32) will exhibit thin…
We introduce a new hybrid method to perform high-resolution tidal disruption simulations, at arbitrary orbits. An SPH code is used to simulate tidal disruptions only in the immediate spatial domain of the star, namely, where the tidal forces dominate over gravity, and then during the fragmentation phase in which the emerging tidal stream may collapse under its own gravity to form fragments. Following each hydrodynamical simulation, an analytical treatment is then applied to instantaneously transfer each fragment back to the tidal sphere for its subsequent disruption, in an iterative process. W…
