Solar System Bodies Research Articles

“The ice-organic-silicate contents of small solar system bodies: indicators for a comet to asteroid evolutionary pathway”

ABSTRACT Comets and asteroids have traditionally been separated categories, but main belt comets skew this view, portraying a possible intermediate stage between these two endmembers. Investigating the relationship between these bodies can improve our understanding of the formation and evolution of the Solar System and help to identify potentially interesting parent bodies from within our solar system, for future sample return missions. Furthermore, elucidating the ice-organic-silicate ratios of potential meteorite parent bodies can help to explain the observed isotopic ratios and petrography of meteorite samples. While the ice-organic-silicate ratios of particular bodies have been estimated, there has been no study undertaken which compares different types of bodies in terms of their ice-organic-silicate ratios. Therefore, this study presents a geophysical-chemical mass balance model, to estimate the ice-organic-silicate ratios of comets, main belt comets and asteroids. The results drawn from the model form a diagonal trend upon an ice-organic-silicate ternary diagram, in which comets and main belt comets plot together at generally higher ice contents, with asteroids typically plotting at lower ice contents. However, an overlap between all three body types is observed and supports the scenario in which comets, main belt comets and asteroids are genetically linked.

Distant trans-Neptunian object candidates from NASA’s TESS mission scrutinized: fainter than predicted or false positives?

ABSTRACT NASA’s Transiting Exoplanet Survey Satellite (TESS) is performing a homogeneous survey of the sky from space in search of transiting exoplanets. The collected data are also being used for detecting passing Solar system objects, including 17 new outer Solar system body candidates located at geocentric distances in the range 80–200 au, that need follow-up observations with ground-based telescope resources for confirmation. Here, we present results of a proof-of-concept mini-survey aimed at recovering two of these candidates that was carried out with the 4.2-m William Herschel Telescope and a QHY600L CMOS camera mounted at its prime focus. For each candidate attempted, we surveyed a square of over 1○ × 1○ around its expected coordinates in Sloan r′. The same patch of sky was revisited in five consecutive or nearly consecutive nights, reaching S/N > 4 at $r^{\prime }\, \lt $23 mag. We focused on the areas of sky around the circumpolar TESS candidates located at (07h:00m:15s, +86○:55′:19″), 202.8 au from Earth, and (06h:39m:47s, +83○:43′:54″) at 162.1 au, but we could not recover either of them at $r^{\prime }\, \le$23 mag. Based on the detailed analysis of the acquired images, we confirm that either both candidates are much fainter than predicted or that they are false positives.

Glycine amino acid transformation under impacts by small solar system bodies, simulated via high-pressure torsion method

Impacts by small solar system bodies (meteoroids, asteroids, comets and transitional objects) are characterized by a combination of energy dynamics and chemical modification on both terrestrial and small solar system bodies. In this context, the discovery of glycine amino acid in meteorites and comets has led to a hypothesis that impacts by astronomical bodies could contribute to delivery and polymerization of amino acids in the early Earth to generate proteins as essential molecules for life. Besides the possibility of abiotic polymerization of glycine, its decomposition by impacts could generate reactive groups to form other essential organic biomolecules. In this study, the high-pressure torsion (HPT) method, as a new platform for simulation of impacts by small solar system bodies, was applied to glycine. In comparison with high-pressure shock experiments, the HPT method simultaneously introduces high pressure and deformation strain. It was found that glycine was not polymerized in the experimental condition assayed, but partially decomposed to ethanol under pressures of 1 and 6 GPa and shear strains of < 120 m/m. The detection of ethanol implies the inherent availability of remaining nitrogen-containing groups, which can incorporate to the formation of other organic molecules at the impact site. In addition, this finding highlights a possibility of the origin of ethanol previously detected in comets.

Modeling Long-Term Photometric Data of Trans-Neptunian Objects and Centaurs

Trans-Neptunian objects and Centaurs are small Solar System bodies that reside in the outer parts of the Solar System. These objects present photometric behaviors that are influenced due to a change in their aspect angle. Using absolute photometric measurements and rotational light-curves at different locations on their orbits allows to model their photometric behavior and obtain physical properties such as pole orientation, shape, density, and even detecting different peculiarities as departure from hydrostatic equilibrium or rings. This work presents how these models are performed to extract different physical properties. A summary of the objects for which their long-term photometric behavior has been modeled is also given.

Presolar grain dynamics: Creating nucleosynthetic variations through a combination of drag and viscous evolution

ABSTRACTMeteoritic studies of Solar system objects show evidence of nucleosynthetic heterogeneities that are inherited from small presolar grains ($\lt 10\,\, \mu {\mathrm{m}}$) formed in stellar environments external to our own. The initial distribution and subsequent evolution of these grains are currently unconstrained. Using 3D, gas-dust simulations, we find that isotopic variations on the order of those observed in the Solar system can be generated and maintained by drag and viscosity. Small grains are dragged radially outwards without size/density sorting by viscous expansion and backreaction, enriching the outer disc with presolar grains. Meanwhile large aggregates composed primarily of silicates drift radially inwards due to drag, further enriching the relative portion of presolar grains in the outer disc and diluting the inner disc. The late accumulation of enriched aggregates outside Jupiter could explain some of the isotopic variations observed in Solar system bodies, such as the enrichment of supernovae derived material in carbonaceous chondrites. We also see evidence for isotopic variations in the inner disc that may hold implications for enstatite and ordinary chondrites that formed closer to the Sun. Initial heterogeneities in the presolar grain distribution that are not continuously reinforced are dispersed by diffusion, radial surface flows, and/or planetary interactions over the entire lifetime of the disc. For younger, more massive discs we expect turbulent diffusion to be even more homogenizing, suggesting that dust evolution played a more central role in forming the isotopic anomalies in the Solar system than originally thought.

Development of Shalbatana Vallis (Mars) by dry volcanic processes

Shalbatana Vallis is a large Martian outflow system that extends into Chryse Planitia from areas of topographic disturbance located north of Ganges Chasma. Development of this system has previously been attributed to processes including: 1) the expulsion of groundwater generated by interactions between magmatic intrusions and ground ice; and 2) the northward conveyance of water along subsurface conduits connected to a deep lake impounded within Ganges Chasma. However, aqueous interpretations of Shalbatana Vallis suffer from weaknesses such as the implausible nature of hypothesized outburst processes, discrepancies between the magnitudes of subsidence that characterize parts of the system and realistic volumes of excess ice that might have once existed in the subsurface, and contradictions between the nature of hypothesized aqueous processes and the mineralogy of associated geological materials. The attributes of Shalbatana Vallis are instead consistent with dry development as a result of the rapid and voluminous effusion of low-viscosity lavas of mafic or ultramafic composition. Volcanic development of the main channel of Shalbatana Vallis is estimated to have required a minimum effusion of ∼360,000 ​km3 of lava, though a total of several times this volume is more likely to have been necessary since channel development cannot be assumed to have taken place with full efficiency. Involved lavas are hypothesized to have been fed by a deeply-rooted igneous plumbing system, and terrain collapse and disturbance located at the head of the system is expected to be partly related to the collapse of intrusions during the latter stages of igneous events. A volcanic origin for Shalbatana Vallis further highlights the critical role played by igneous processes in channel development on rocky bodies of the inner solar system.

Infrared Spectroscopic Study of Methane Ice, Pure and in Mixtures with Polar (H2O) and Nonpolar (N2) Molecules.

Mid-infrared studies of fundamental modes of ices of pure CH4 and its mixtures with polar (H2O) and nonpolar (e.g., N2) molecules are essential in order to learn the state of aggregation and thermal history of ices present in the interstellar medium and outer solar system bodies. Such data will be useful in the interpretation of observational data from the James Webb Space Telescope. Using an ultrahigh vacuum apparatus, we conducted reflection–absorption infrared spectroscopy measurements in the mid-IR range of pure methane ice and methane-containing ice mixtures of interest to interstellar and solar system ice chemistry, e.g., with H2O and N2 molecules. We found that nuclear spin conversion (NSC) in solid methane and its crystalline structures is affected—in different ways—by the presence of H2O and N2. Specifically, we found a relationship between the thickness and the solid-state ordering transformation in methane thin films. This new study of the NSC of pure CH4 ice and of the CH4:H2O ice mixture at 7 K is carried out in relation to the segregation of H2O using the ν1 and ν2 IR inactive modes of methane. The diffusion of N2 and CH4 in the CH4:N2 ice mixture with temperature cycling has been studied to obtain the relationship between IR features and the state of aggregation of the ice.

The SKA as a Prebiotic Molecule Detector

One of the theories for the origin of life proposes that a significant fraction of prebiotic material could have arrived to Earth from outer space between 4.1 and 3.8 billion years ago. This suggests that those prebiotic compounds could have originated in interstellar space, to be later on incorporated to small Solar-system bodies and planetesimals. The recent discovery of prebiotic molecules such as hydroxylamine and ethanolamine in the interstellar medium, strongly supports this hypothesis. However, some species such as sugars, key for the synthesis of ribonucleotides and for metabolic processes, remain to be discovered in space. The unmatched sensitivity of the Square Kilometre Array (SKA) at centimeter wavelengths will be able to detect even more complex and heavier prebiotic molecules than existing instrumentation. In this contribution, we illustrate the potential of the SKA to detect simple sugars with three and four carbon atoms, using a moderate investment of observing time.

SISPO: Space Imaging Simulator for Proximity Operations.

This paper describes the architecture and demonstrates the capabilities of a newly developed, physically-based imaging simulator environment called SISPO, developed for small solar system body fly-by and terrestrial planet surface mission simulations. The image simulator utilises the open-source 3-D visualisation system Blender and its Cycles rendering engine, which supports physically based rendering capabilities and procedural micropolygon displacement texture generation. The simulator concentrates on realistic surface rendering and has supplementary models to produce realistic dust- and gas-environment optical models for comets and active asteroids. The framework also includes tools to simulate the most common image aberrations, such as tangential and sagittal astigmatism, internal and external comatic aberration, and simple geometric distortions. The model framework's primary objective is to support small-body space mission design by allowing better simulations for characterisation of imaging instrument performance, assisting mission planning, and developing computer-vision algorithms. SISPO allows the simulation of trajectories, light parameters and camera's intrinsic parameters.

Serpentinization in the Thermal Evolution of Icy Kuiper Belt Objects in the Early Solar System

Abstract Here we present an improved algorithm to model the serpentinization process in planetesimals in the early solar system. Although it is hypothesized that serpentinization-like reactions played an important role in the thermal evolution of planetesimals, few and restricted models are available in this topic. These processes may be important, as the materials involved were abundant in these objects. Our model is based on the model by Góbi &amp; Kereszturi and contains improvements in the consideration of heat capacities and lithospheric pressure and in the calculation of the amount of interfacial water. Comparison of our results with previous calculations shows that there are significant differences in, e.g., the serpentinization time—the time necessary to consume most of the reactants at specific initial conditions—or the amount of heat produced by this process. In a simple application we show that in icy bodies, under some realistic conditions, below the melting point of water ice, serpentinization reaction using interfacial water may be able to proceed and eventually push the local temperature above the melting point to start a “runaway” serpentinization. According to our calculations in objects with radii R ≳ 200 km, serpentinization might have quickly reformed nearly the whole interior of these bodies in the early solar system.

A Model Earth-sized Planet in the Habitable Zone of α Centauri A/B

Abstract The bulk chemical composition and interior structure of rocky exoplanets are fundamentally important to understand their long-term evolution and potential habitability. Observations of the chemical compositions of solar system rocky bodies and of other planetary systems have increasingly shown a concordant picture that the chemical composition of rocky planets reflects that of their host stars for refractory elements, whereas this expression breaks down for volatiles. This behavior is explained by devolatilization during planetary formation and early evolution. Here we apply a devolatilization model calibrated with solar system bodies to the chemical composition of our nearest Sun-like stars—α Centauri A and B—to estimate the bulk composition of any habitable-zone rocky planet in this binary system (“α-Cen-Earth”). Through further modeling of likely planetary interiors and early atmospheres, we find that, compared to Earth, such a planet is expected to have (i) a reduced (primitive) mantle that is similarly dominated by silicates, albeit enriched in carbon-bearing species (graphite/diamond); (ii) a slightly larger iron core, with a core mass fraction of 38.4 − 5.1 + 4.7 wt% (see Earth’s 32.5 ± 0.3 wt%); (iii) an equivalent water-storage capacity; and (iv) a CO2–CH4–H2O-dominated early atmosphere that resembles that of Archean Earth. Further taking into account its ∼25% lower intrinsic radiogenic heating from long-lived radionuclides, an ancient α-Cen-Earth (∼1.5–2.5 Gyr older than Earth) is expected to have less efficient mantle convection and planetary resurfacing, with a potentially prolonged history of stagnant-lid regimes.

Low-cost Access to the Deep, High-cadence Sky: the Argus Optical Array

New mass-produced, wide-field, small-aperture telescopes have the potential to revolutionize ground-based astronomy by greatly reducing the cost of collecting area. In this paper, we introduce a new class of large telescope based on these advances: an all-sky, arcsecond-resolution, 1000 telescope array which builds a simultaneously high-cadence and deep survey by observing the entire sky all night. As a concrete example, we describe the Argus Array, a 5 m-class telescope with an all-sky field of view and the ability to reach extremely high cadences using low-noise CMOS detectors. Each 55 GPix Argus exposure covers 20% of the entire sky to m g = 19.6 each minute and m g = 21.9 each hour; a high-speed mode will allow sub-second survey cadences for short times. Deep coadds will reach m g = 23.6 every five nights over 47% of the sky; a larger-aperture array telescope, with an étendue close to the Rubin Observatory, could reach m g = 24.3 in five nights. These arrays can build two-color, million-epoch movies of the sky, enabling sensitive and rapid searches for high-speed transients, fast-radio-burst counterparts, gravitational-wave counterparts, exoplanet microlensing events, occultations by distant solar system bodies, and myriad other phenomena. An array of O(1000) telescopes, however, would be one of the most complex astronomical instruments yet built. Standard arrays with hundreds of tracking mounts entail thousands of moving parts and exposed optics, and maintenance costs would rapidly outpace the mass-produced-hardware cost savings compared to a monolithic large telescope. We discuss how to greatly reduce operations costs by placing all optics in thermally controlled, sealed domes with only a few moving parts. Coupled with careful software scope control and use of existing pipelines, we show that the Argus Array could become the deepest and fastest Northern sky survey, with total costs in the $20M range.

The absence of an effect of nickel on iron isotope fractionation during core formation

The Fe isotopic compositions of mantles of differentiated inner solar system bodies are similar to, or heavier than those of chondritic meteorites. Core–mantle differentiation is a potential contributor to planetary isotopic fractionation. However, previous metal–silicate experiments provide only equivocal evidence for such fractionation, and have been used to argue that the Ni content of core-forming metal influences the extent of Fe isotopic fractionation. Here, we complement existing data with twenty-two novel metal–silicate equilibrium experiments with varying Ni content to better quantify the effect of Ni on the vector and magnitude of Fe isotopic fractionation during core formation. We find no statistically resolvable effect of the Ni content in the metallic phase on the metal–silicate Fe isotopic fractionation factor over a wide range of Ni concentrations (0–70 wt.% in the metal). In particular, the Fe isotopic composition of alloys from two experiments performed with 70 wt.% of Ni (δ56Femetal = 0.27 ± 0.04‰ and 0.32 ± 0.03‰, 2 standard deviations σ) are identical to the bulk experimental starting material (δ56Febulk = 0.27 ± 0.10‰, 2σ). Our data across all experiments yield an average isotopic fractionation factor Δ56Femet–sil = 0.05 ± 0.22‰ (2σ) at 1873 K and 1–2 GPa, suggesting that little to no isotopic fractionation of Fe is expected to occur during core formation at low pressures. As such, our data does not support core formation as the main mechanism causing the observed variability in Fe isotope ratios between the silicate Earth, Moon, Vesta and other differentiated asteroids. A combination of multiple accretion-related processes—including condensation from the solar nebula, volatile-depleting events such as giant impacts, and the disproportionation of ferrous iron to ferric iron and iron metal in larger bodies—as well as deep mantle and recycling processes could explain the heavier-than-chondritic signatures in the silicate Earth and Moon. Furthermore, our results support the ideality of mixing among Fe–Ni alloys, as previously demonstrated for physical properties but less conclusively evidenced for chemical properties.

A Remote Sensing Perspective on Mass Wasting in Contrasting Planetary Environments: Cases of the Moon and Ceres

Mass wasting, as one of the most significant geomorphological processes, contributes immensely to planetary landscape evolution. The frequency and diversity of mass wasting features on any planetary body also put engineering constraints on its robotic exploration. Mass wasting on other Solar System bodies shares similar, although not identical, morphological characteristics with its terrestrial counterpart, indicating a possible common nature for their formation. Thus, planetary bodies with contrasting environmental conditions might help reveal the effects of the atmosphere, subsurface fluids, mass accumulation/precipitation, and seismicity on mass wasting, and vice versa. Their relative positions within our Solar System and the environmental and geophysical conditions on the Moon and the dwarf planet Ceres are not only extremely different from Earth’s but from each other too. Their smaller sizes coupled with the availability of global-scale remote sensing datasets make them ideal candidates to understand mass wasting processes in widely contrasting planetary environments. Through this concept article, we highlight several recent advances in and prospects of using remote sensing datasets to reveal unprecedented details on lunar and Cerean mass wasting processes. We start with briefly discussing several recent studies on mass wasting using Lunar Reconnaissance Orbiter Camera (LROC) data for the Moon and Dawn spacecraft data for Ceres. We further identify the prospects of available remote sensing data in advancing our understanding of mass wasting processes under reduced gravity and in a scant (or absent) atmosphere, and we conclude the article by suggesting future research directions.

Assessment of the feasibility of space-based stellar occultation observations of Uranus and Neptune

UV occultation measurements made by Voyager 2 of the upper atmospheres of Uranus and Neptune in the late 1980s found both planets contain warm stratospheres and extremely hot thermospheres. Sunlight reaching the ice giants is far too weak to account for these reported temperatures. This is sometimes called the Giant Planet Energy Crisis. Theorized mechanisms to account for the heating observed at Uranus and Neptune suffer from a dearth of reliable observations. A similar energy crisis was reported from Voyager observations of Jupiter and Saturn, but observations made by the Galileo, Juno, and Cassini-Huygens missions as well as from ground-based facilities have vastly improved efforts to understand upper atmospheric heating. For Uranus and Neptune, Earth-based stellar occultation observations can fill in this significant gap in observations and produce reliable atmospheric measurements. These measurements can also assist in motivating and planning for a flagship mission to either ice giant.A stellar occultation occurs when a solar system body passes across the line of sight from an observer to a star. Refraction of starlight by the upper atmosphere of the occulting body is observed as a light curve and can be used to sample the temperature structure with high vertical resolution. In this paper, we demonstrate that observing stellar occultations by Uranus and Neptune from satellites in low-Earth orbit can make high-quality upper atmospheric measurements of the Ice Giants. Such observations would not be subjected to atmospheric scintillation or disruption due to weather and could be observed at any time of day. We predict that from 2025 through 2035, as many as 56 Uranus and 14 Neptune occultations could be observed from orbit, compared to 20 Uranus and 6 Neptune events from the ground. We find many of these events can be observed with comparable or higher signal-to-noise via a small, Earth-orbiting satellite than a large ground-based observatory and encourage others to explore the launch feasibility of one or more such missions.

Concepts for the Future Exploration of Dwarf Planet Ceres’ Habitability

Abstract Dwarf planet Ceres is a compelling target for future exploration because it hosts at least regional brine reservoirs and potentially ongoing geological activity. As the most water-rich body in the inner solar system, it is a representative of a population of planetesimals that were likely a significant source of volatiles and organics to the inner solar system. Here we describe possible medium-class (around $1 billion) mission concepts that would determine both Ceres’ origin and its current habitability potential. Habitability is addressed through a combination of geological, geophysical, and compositional investigations by (i) searching for evidence from orbit of past and ongoing geological activity near landforms interpreted as brine-driven volcanic structures and (ii) probing the brine distribution below one of these regions with electromagnetic sounding (in situ). Two approaches were considered for compositional measurements, which address both habitability and origins: (1) in situ exploration at two sites and (2) sample return from a single site. Both concepts targeted material at Occator crater, which is one of the youngest features on Ceres (∼20 Ma) and a site rich in evaporites evolved from recently erupted brine sourced from a region &gt;35 km deep. We conclude that a sample return architecture from these young evaporite deposits offers greater science return by enabling high-resolution analysis of organic matter (trapped in salt minerals) and isotopes of refractory elements for a similar cost and less science risk than in situ analyses. This manuscript describes the six science objectives and the two implementation concepts considered to achieve those objectives.

Assessing poroelastic properties of a geothermal reservoir by tidal signal analysis

The gravitational attractions of the solar-system bodies cause tidal phenomena, in response to which the pore pressure of geothermal fields often exhibits diurnal and semidiurnal fluctuations. Such periodic fluctuations can be quantified in relation to the Earth tides and atmospheric loading, which are functions of reservoir poroelastic properties. In this study, the relationship between the poroelastic properties and the tidal effects was formulated and examined graphically. The dependencies of individual properties on the Earth tides and atmospheric loading are different, and clarifying such relationships helps us systematically understand the assessment of poroelastic properties using tidal signals. The analysis method was applied to the actual pressure data acquired at an onshore geothermal field in Japan. The resultant estimates of reservoir properties were reasonable and affirmed the practical applicability of the methodology to geothermal reservoirs. The sensitivity of the property estimations to the prescribed values was examined and constraining the upper bound of Poisson's ratio was found to be important for assessing poroelastic properties. The tidal signal analysis only requires the reservoir pressure transients and barometric pressure without any further well interventions, and thus can provide a safe and cost-effective in situ reservoir property assessment.

A bimodal distribution of haze in Pluto\u2019s atmosphere

Pluto, Titan, and Triton make up a unique class of solar system bodies, with icy surfaces and chemically reducing atmospheres rich in organic photochemistry and haze formation. Hazes play important roles in these atmospheres, with physical and chemical processes highly dependent on particle sizes, but the haze size distribution in reducing atmospheres is currently poorly understood. Here we report observational evidence that Pluto’s haze particles are bimodally distributed, which successfully reproduces the full phase scattering observations from New Horizons. Combined with previous simulations of Titan’s haze, this result suggests that haze particles in reducing atmospheres undergo rapid shape change near pressure levels ~0.5 Pa and favors a photochemical rather than a dynamical origin for the formation of Titan’s detached haze. It also demonstrates that both oxidizing and reducing atmospheres can produce multi-modal hazes, and encourages reanalysis of observations of hazes on Titan and Triton.

SORA: Stellar occultation reduction and analysis

ABSTRACT The stellar occultation technique provides competitive accuracy in determining the sizes, shapes, astrometry, etc., of the occulting body, comparable to in-situ observations by spacecraft. With the increase in the number of known Solar system objects expected from the LSST, the highly precise astrometric catalogs, such as Gaia, and the improvement of ephemerides, occultations observations will become more common with a higher number of chords in each observation. In the context of the Big Data era, we developed sora, an open-source python library to reduce and analyse stellar occultation data efficiently. It includes routines from predicting such events up to the determination of Solar system bodies’ sizes, shapes, and positions.

Research in Analog Environments to Enable Studies of Ocean Worlds

Analog environments on Earth enable scientists to answer research questions about extraterrestrial ocean worlds that would be otherwise inaccessible. Because of their relative ease of sampling and close proximity to research facilities, utilization of analog environments allows scientists to undertake many investigations for the cost of a single planetary mission. In addition to direct in situ sampling, modeling approaches can be useful as can cost-effective tools both for determining whether a moon or planet is a suitable Earth analog and for designing strategies to sample extraterrestrial analog environments. Reconfigured Earth system models can help determine if conditions on other ocean worlds are suitable to support life. Finally, space exploration has made the protection of Earth’s environment and other solar system bodies from harmful contamination a high priority at both the national and international levels. Because NASA’s planetary exploration priorities emphasize robotic exploration, the US National Academies recently recommended that studies, workshops, and brainstorming sessions organized by NASA and other space agencies need to include a sufficiently broad range of microbiologists to ensure planetary protection. This will require the development and implementation of mechanisms for creating partnerships between Earth scientists and planetary scientists to test planetary protection solutions at field analog sites.