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Multiwavelength Observations of Recent Comets

Comets provide important clues to the physical and chemical processes that occurred during the formation and early evolution of the Solar System, and could also have been important for initiating prebiotic chemistry on the early Earth. Comets are comprised of molecular ices, that may be pristine inter-stellar remnants of Solar System formation, along with high-temperature crystalline silicate dust that is indicative of a more thermally varied history in the protosolar nebula. Comparing abundances of cometary parent volatiles, and isotopic fractionation ratios, to those found in the interstellar medium, in disks around young stars, and between cometary families, is vital to understanding planetary system formation and the processing history experienced by organic matter in the so-called interstellar-comet connection. We will present a comparison of molecular abundances in these comets to those observed in others, supporting a long-term effort of building a comet taxonomy based on composition.

ground-based observations↗

New Perspectives on Ancient Mars

Global data sets returned by the Mars Global Surveyor (MGS), Mars Odyssey, and Mars Express spacecraft and recent analyses of Martian meteorites suggest that most of the major geological events of Martian history occurred within the first billion years of solar system formation. This period was a time of heavy impact bombardment of the inner solar system, a process that strongly overprinted much of the Martian geological record from that time. Geophysical signatures nonetheless remain from that period in the Martian crust, and several geochemical tracers of early events are found in Martian meteorites. Collectively, these observations provide insight into the earliest era in Martian history when the conditions favoring life were best satisfied.

Solomon, Sean C.↗

NASA's Near-Earth Object Office

Near-Earth Objects (NEOs) are scientifically interesting remnants of the early solar system formation process, accessible resources for the raw materials necessary for colonizing the inner solar system in the next century, and objects that can threaten life on Earth.

Near Earth Objects Comets Asteroids↗

National Academy of Science, Engineering, and Medicine, NASA Planetary Science and Astrobiology Decadal Survey (Chapter 3)

Our inner Solar System has the four terrestrial planets, Mercury, Venus, Earth, and Mars, along with Earth’s large Moon, two small moons of Mars, dwarf planet Ceres, numerous 100-km class asteroids, and a multitude of small bodies that populate the asteroid belt and the inner planet region. To what extent does this structure reflect a deterministic outcome of general Solar System formation processes, and how much of it is instead a consequence of stochastic events that would change in unpredictable ways if the system’s formation could be rerun? This fundamental question motivates scientific investigations of the inner Solar System, with implications not only for understanding our own planet’s origin but also for the origin of planetary systems and Earth-like planets beyond our own.

79 ASTRONOMY AND ASTROPHYSICS↗

What Could Be Learned About the Geochronology of Mars from Samples Collected by M-2020

Based on meteoritic evidence, Mars accreted as early as 2 Ma after the formation of the first solids in the solar system from material with an O-Ti-Cr-Ni isotopic provenance distinct from the Earth- Moon system. It likely formed a magma ocean within approx. 100 Ma after solar system formation, from which the martian core last equilibrated with its mantle at pressures of approx. 14 GPa. The formation of most of the mass of the Martian crust is constrained to have occurred by 4.35 Ga. Remanent magnetization in martian meteorite ALH 84001 demonstrates a dynamo had initiated on Mars at or before 4.1 Ga. Sample return is necessary because meteorites lack geologic context and their orientation with respect to the paleomagnetic field is not known.

Source record↗

The Solar System calcium isotopic composition inferred from Ryugu samples

The Hayabusa2 spacecraft has returned samples from the Cb-type asteroid (162173) Ryugu to Earth. Previous petrological and chemical analyses support a close link between Ryugu and CI chondrites that are presumed to be chemically the most primitive meteorites with a solar-like composition. However, Ryugu samples are highly enriched in Ca compared to typical CI chondrites. To identify the cause of this discrepancy, here we report stable Ca isotopic data (expressed as δ 44/40 Ca SRM915a ) for returned Ryugu samples collected from two sites. We found that samples from both sites have similar δ 44/40 Ca SRM915a (0.58 ± 0.03 ‰ and 0.55 ± 0.08 ‰, 2 s.d.) that fall within the range defined by CIs. This isotopic similarity suggests that the Ca budget of CIs and Ryugu samples is dominated by carbonates, and the variably higher Ca contents in Ryugu samples are due to the abundant carbonates. Precipitation of carbonates on Ryugu likely coincided with a major episode of aqueous activity dated to have occurred ~5 Myr after Solar System formation. Based on the pristine Ryugu samples, the average δ 44/40 Ca SRM915a of the Solar System is defined to be 0.57 ± 0.04 ‰ (2 s.d.).

79 ASTRONOMY AND ASTROPHYSICS↗

Synergistic Activities of Near-Earth Object Exploration

U.S. President Obama stated on April 15, 2010 that the next goal for human spaceflight will be to send human beings to near-Earth asteroids by 2025. Missions to NEOs would undoubtedly provide a great deal of technical and engineering data on spacecraft operations for future human space exploration while conducting in-depth scientific examinations of these primitive objects. Information obtained from a human investigation of a NEO, together with ground-based observations and prior spacecraft investigations of asteroids and comets, will also provide a real measure of ground truth to data obtained from terrestrial meteorite collections. Major advances in the areas of geochemistry, impact history, thermal history, isotope analyses, mineralogy, space weathering, formation ages, thermal inertias, volatile content, source regions, solar system formation, etc. can be expected from human NEO missions. Samples directly returned from a primitive body would lead to the same kind of breakthroughs for understanding NEOs that the Apollo samples provided for understanding the Earth-Moon system and its formation history. In addition, robotic precursor and human exploration missions to NEOs would allow the NASA and its international partners to gain operational experience in performing complex tasks (e.g., sample collection, deployment of payloads, retrieval of payloads, etc.) with crew, robots, and spacecraft under microgravity conditions at or near the surface of a small body. This would provide an important synergy between the worldwide Science and Exploration communities, which will be crucial for development of future international deep space exploration architectures and has potential benefits for future exploration of other destinations beyond low-Earth orbit.

Abell, Paul↗

Exploration of Near-Earth Asteroids

A major goal for NASA's human spaceflight program is to send astronauts to near-Earth asteroids (NEAs) in the coming decades. Missions to NEAs would undoubtedly provide a great deal of technical and engineering data on spacecraft operations for future human space exploration while conducting in-depth scientific examinations of these primitive objects. However, prior to sending human explorers to NEAs, robotic investigations of these bodies would be required in order to maximize operational efficiency and reduce mission risk. These precursor missions to NEAs would fill crucial strategic knowledge gaps concerning their physical characteristics that are relevant for human exploration of these relatively unknown destinations. Information obtained from a human investigation of a NEA, together with ground-based observations and prior spacecraft investigations of asteroids and comets, will also provide a real measure of ground truth to data obtained from terrestrial meteorite collections. Major advances in the areas of geochemistry, impact history, thermal history, isotope analyses, mineralogy, space weathering, formation ages, thermal inertias, volatile content, source regions, solar system formation, etc. can be expected from human NEA missions. Samples directly returned from a primitive body would lead to the same kind of breakthroughs for understanding NEAs that the Apollo samples provided for understanding the Earth-Moon system and its formation history. In addition, robotic precursor and human exploration missions to NEAs would allow the NASA and its international partners to gain operational experience in performing complex tasks (e.g., sample collection, deployment of payloads, retrieval of payloads, etc.) with crew, robots, and spacecraft under microgravity conditions at or near the surface of a small body. This would provide an important synergy between the worldwide Science and Exploration communities, which will be crucial for development of future international deep space exploration architectures and has potential benefits for future exploration of other destinations beyond low-Earth orbit.

Abell, Paul↗

Partitioning of U, Th and K Between Metal, Sulfide and Silicate, Insights into the Volatile-Content of Mercury

During the early stages of the Solar System formation, especially during the T-Tauri phase, the Sun emitted strong solar winds, which are thought to have expelled a portion of the volatile elements from the inner solar system. It is therefore usually believed that the volatile depletion of a planet is correlated with its proximity to the Sun. This trend was supported by the K/Th and K/U ratios of Venus, the Earth, and Mars. Prior to the MESSENGER mission, it was expected that Mercury is the most volatile-depleted planet. However, the Gamma Ray Spectrometer of MESSENGER spacecraft revealed elevated K/U and K/Th ratios for the surface of Mercury, much higher than previous expectations. It is possible that the K/Th and K/U ratios on the surface are not a reliable gauge of the bulk volatile content of Mercury. Mercury is enriched in sulfur and is the most reduced of the terrestrial planets, with oxygen fugacity (fO2) between IW-6.3 and IW-2.6 log units. At these particular compositions, U, Th and K behave differently and can become more siderophile or chalcophile. If significant amounts of U and Th are sequestered in the core, the apparent K/U and K/Th ratios measured on the surface may not represent the volatile budget of the whole planet. An accurate determination of the partitioning of these elements between silicate, metal, and sulfide phases under Mercurian conditions is therefore essential to better constrain Mercury's volatile content and assess planetary formation models.

Habermann, M.↗

Star formation and extinct radioactivities

An assessment is made of the evidence for the existence of now-extinct radioactivities in primitive solar system material, giving attention to implications for the early stages of sun and solar system formation. The characteristics of possible disturbances in dense molecular clouds which can initiate the formation of cloud cores is discussed, with emphasis on these disturbances able to generate fresh radioactivities. A one-solar mass red giant star on the asymptotic giant branch appears to have been the best candidate to account for the short-lived extinct radioactivities in the early solar system.

Cameron, A. G. W.↗

Geology Before Pluto: Pre-Encounter Considerations

Pluto, its large satellite Charon, and its four known satellites represent the first trans-Neptunian Kuiper Belt objects populating the outer-most solar system beyond the gas giant planets to be studied in detail from a spacecraft (New Horizons). A complete picture of the solar nebula, and solar system formation cannot be confidently formulated until representatives of this group of bodies at the edge of solar space have been examined. The Pluto system is composed of unique lunar- and intermediate-sized objects that can tell us much about how objects with volatile icy compositions evolve. Modeling of the interior suggests that geologic activity may have been to some degree, and observations of frost on the surface could imply the need for a geologic reservoir for the replenishment of these phases. However, the putative indicators of Pluto's geologic history are inconclusive and unspecific. Detailed examination of Pluto's geologic record is the only plausible means of bridging the gap between theory and observations. In this talk I will examine the potential importance of these tentative indications of geologic activity and how specific spacecraft observations have been designed and used to constrain the Pluto system's geologic history. The cameras of New Horizons will provide robust data sets that should be immanently amenable to geological analysis of the Pluto System's landscapes. In this talk, we begin with a brief discussion of the planned observations by New Horizons' cameras that will bear most directly on geological interpretability. Then I will broadly review major geological processes that could potentially operate of the surfaces of Pluto and its moons. I will first survey exogenic processes (i.e., those for which energy for surface modification is supplied externally to the planetary surface): impact cratering, sedimentary processes (including volatile migration) and the work of wind. I will conclude with an assessment of prospects for endogenic activity in the form of tectonics and cryo-volcanism.

Pluto↗

The Hummingbird GC-IMS: In Situ Analysis of a Cometary Nucleus

Comets are of enormous scientific interest for many reasons. They are primitive bodies that date back to the earliest stages of solar system formation and, because of their small size and because they have been stored in the outer reaches of the solar system, their pristine nature has been preserved better than for any other class of body. They are extremely rich in highly volatile elements, many in the form of ices, and are richer in organic matter than any other known solar system body. It is strongly suspected that in addition to their content of primordial solar nebular material, they also incorporate unprocessed matter from the interstellar medium. Impacts by comets occur onto all the planets and satellites, often with major consequences (e.g., the dinosaur extinction event at the KIT boundary), or sometimes just providing a spectacular cosmic event (e.g., the collision of comet Shoemaker-Levy 9 with Jupiter). A mission to analyze a cometary nucleus must be capable of detecting and identifying over 30 molecular species among several different chemical groups. The Hummingbird Mission will rendezvous with, orbit, characterize, and make multiple descents to the nucleus of a comet. Hummingbird will employ a Gas Chromatograph - Ion Mobility Spectrometer (GC-IMS) as part-of a suite of sophisticated instruments for a comprehensive in situ elemental, molecular, and isotopic analysis of the comet.

Kojiro, Daniel R.↗

HEAO 3 discovery of Al-26 in the interstellar medium

A new analysis technique was used with HEAO 3 satellite gamma ray data to quantify the galactic 1809 keV emission. A method of bins was applied in summing for specific scan directions, followed by fitting the source and background components. The 1809 keV line of Al-26 was significant because of the recent discovery that Al-26 was overabundant in meteoritic material and implanted during solar system formation. The HEAO 3 flux indicated a current decay of 3 solar masses of Al-26 per year in the interstellar medium, possibly occurring in red giants and massive main sequence stars. The ratio of the observed Al-26 to the Al-27 flux was similar to that measured in meteorites, which suggests that the ratio is normal for the galactic medium and that no supernova triggered the protosolar nebular collapse.

Mahoney, W. A.↗

On The Ultimate Fate of Interplanetary Dust

Interplanetary dust is interesting both from a physical point of view and from the awareness that the population poses a substantial collision risk to manned and unmanned spacecraft alike. Insight into the time evolution of the population gives important insights into solar system formation and, we argue, will offer clues as to the behavior of solar cycles predating modern ways of viewing the sun (e.g., sun spot counting, magnetograms, etc.). In addition, knowing how the dust population moves under the variety of forces each grain experiences will inform and better prepare manned and robotic spacecraft missions to mitigate the risk posed by dust. With these aims in mind, we developed a simple dynamical model for dust motion based on the work of Czechowski and Mann [1]. A byproduct of that development is a clear analytic model that demonstrates how the interplay of the Poynting-Robertson and Lorenz perturbation forces on the Keplerian motion of charged dust grains around the Sun can result in dust populations that move inward, outward, or remain confined in annular rings about the Sun. The timing of any of these behaviors is strongly dependent on the physical properties of the grain (mass, charge and reflectivity) and the evolution of the Sun’s dipole field.

Force models↗

Supernovae, grains and the formation of the solar system

An investigation is conducted concerning the possibility that observed Mg-26 anomalies in meteorites may be related to a nucleosynthetic event which preceded the formation of the solar system by at most a few million years. The Al-26, which decayed to form the observed excess Mg-26, could have been produced in either explosive carbon burning or in a high temperature carbon burning shell source immediately preceding the explosion. The results of supernova grain condensation calculations are presented and related to the hypothesis that a 'last event' supernova was indeed related to the formation of the solar system and thus might have created the observed isotopic anomalies in magnesium, oxygen, neon, and xenon.

Lattimer, J. M.↗

Mission Architecture and Technology Options for a Flagship Class Venus In Situ Mission

Venus, as part of the inner triad with Earth and Mars, represents an important exploration target if we want to learn more about solar system formation and evolution. Comparative planetology could also elucidate the differences between the past, present, and future of these three planets, and can help with the characterization of potential habitable zones in our solar system and, by extension, extrasolar systems. A long lived in situ Venus mission concept, called the Venus Mobile Explorer, was prominently featured in NASA's 2006 SSE Roadmap and supported in the community White Paper by the Venus Exploration Analysis Group (VEXAG). Long-lived in situ missions are expected to belong to the largest (Flagship) mission class, which would require both enabling and enhancing technologies beside mission architecture options. Furthermore, extreme environment mitigation technologies for Venus are considered long lead development items and are expected to require technology development through a dedicated program. To better understand programmatic and technology needs and the motivating science behind them, in this fiscal year (FY08) NASA is funding a Venus Flaghip class mission study, based on key science and technology drivers identified by a NASA appointed Venus Science and Technology Definition Team (STDT). These mission drivers are then assembled around a suitable mission architecture to further refine technology and cost elements. In this paper we will discuss the connection between the final mission architecture and the connected technology drivers from this NASA funded study, which - if funded - could enable a future Flagship class Venus mission and potentially drive a proposed Venus technology development program.

Balint, Tibor S.↗

The solar system/interstellar medium connection - Gas phase abundances

Gas-phase abundances in the outer solar system are presented as diagnostics of the interstellar medium at the time of the solar system formation, some 4.55 billion years ago. Possible influences of the thermal and chemical histories of the primitive solar nebula and of the processes which led to the formation and evolution of the outer planets and comets on the elemental and molecular composition of the primordial matter are outlined. The major components of the atmospheres of the outer planets and of the comae of comets are identified, and the cosmogonical and cosmological implications are discussed.

Lutz, Barry L.↗

Evolution of the Preliminary Fault Management Architecture and Design for the Psyche Mission

The Psyche Mission presents the first opportunity toexplore the largest metal asteroid in the solar system, (16)Psyche, which is believed to be the exposed core of a largerplanetesimal that was stripped of its rocky mantle throughmultiple collisions during early solar system formation. Themission was selected in January 2017 for a 2022 launch as partof NASA’s Discovery Program and is uniquely enabled by theintegration of a Solar Electric Propulsion (SEP) Chassisdelivered by Maxar Space Solutions with JPL’s core deepspace avionics, flight software, and fault managementarchitectures. One of the key design tasks is the development ofa fault management system capable of being responsive to theunique elements of the combined JPL and Maxar spacecraftarchitecture. This new design leverages the strengths of eachorganization, with Maxar delivering its well-proven highvoltage power bus and low-thrust electric propulsionsubsystem from its GEO communications satellite product line,and JPL delivering its deep space mission expertise and thehardware and software most critical to deep space missiondesign. The development of a robust low-thrust mission andthe integration of design philosophies and hardware from twoorganizations is not without its challenges though.A key challenge in the development of the Psyche faultmanagement architecture and design is in the integration ofdesign philosophies and hardware from JPL and Maxar. Atthe architecture level, Maxar GEO communications satellitesare developed under the premise of highly responsive groundin the loop for the resolution of anomalies, and theimplementation takes a fail-operational approach to minimizedown time for its customers. In contrast, a deep space missionmust be able to maintain safety with long periods of groundcommunication outage. Additionally, with no time-criticalevents after launch, the Psyche spacecraft will generally failsafe in the presence of anomalous conditions; specialconsideration is being given to this approach, however, tominimize the loss of electric propulsion thrust time, which iscritical to low-thrust missions. At the hardware level, thedetailed definition of interfaces between JPL and Maxarhardware presents a unique challenge in the development andflowdown of fault management requirements, the developmentand implementation of fault monitors and responses, and thedevelopment and verification of fault containment boundaries.This paper describes the evolution of the Psyche faultmanagement architecture and design from the concept studyinto the preliminary design phase, with a focus on the uniquechallenges associated with flying GEO communicationssatellite hardware in deep space, implementing a robust lowthrust mission, and the integration of design philosophies andhardware from JPL and Maxar. Details regarding how thesechallenges are addressed in the fault management design inorder to maximize heritage, leverage the strengths of eachorganization, and minimize risk across the design are alsodiscussed.

Marsh, Danielle↗