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NASA NTRSDate not supplied

Trace Element and Isotopic Evidence for Bennu's Primitive Provenance

The delivery of material from asteroid (101955) Bennu by NASA’s OSIRIS-REx mission provides the opportunity to investigate some of the most pristine material from the early Solar System [1]. Our team at Lawrence LivermoreNational Laboratory (LLNL) utilized the equivalent of 5.0 mg from Bennu sampleOREX-803015-100 to quantify the major and trace element contents and investigate major element isotopics (Ca, Ti, Cr, Fe, and Ni). Our 5.0 mg aliquot ofOREX-803015-100 was a subsample of dissolved homogenized material representing 20.66 mg [2]. A separate 5.0 mg aliquot was sent to ETH Zürich and is discussed in a companion abstract [3]. Before any chemical separation on our 5.0 mg aliquot, the equivalent of 0.5 mg was removed and analyzed for elemental abundances at LLNL using a ThermoScientific Element XR. Our data agree exceptionally well with those reported by[2], showing that Bennu is primitive and compositionally similar to CI chondrites, Ryugu [4], and the solar photosphere [5]. The remaining ~4.5 mg underwent purification procedures to chemically isolate and purify Ca, Ti, Cr, Fe, and Ni from one another and the sample matrix. Their isotopic compositions were measured on either the Triton TIMS (Ca) at JohnsonSpace Center in Houston, Neoma MC-ICPMS (Ti, Cr) at LLNL, or the Neptune MC-ICPMS (Fe, Ni) at LLNL. Results from the Ca, Ti, Cr, Fe, and Ni isotopic compositions suggest that Bennu is closely related to CI chondrites—consistent with conclusions from elemental composition [2] and oxygen isotopics [6]reported for Bennu. The major element isotope compositions that we will present demonstrate that Bennu likely formed in a similar region of the SolarSystem as CI chondrites and potentially at a similar time of Solar System evolution.

Greg Brennecka↗
NASA NTRS1993

Origins of Solar Systems Workshop: The Origin, Evolution, and Detectability of Short Period Comets

The origin of the short period comets (SPC) (periods less than 200 years), the dynamical formation of their present reservoir(s), the cause and rate of their transport to the inner planetary region where they can be detected, and the magnitude of selection effects in their discovery are important research questions directly coupled to the goals of understanding the origin and evolution of the Solar System. To address these questions in an intensive way, an interdisciplinary, five month long Workshop from Jan. to May 1993 at Southwest Research Institute (SwRI) in San Antonio was convened. The goal of this Workshop was to advance the state of understanding about the origins, dynamical evolution, and present location of short period comets and their reservoir(s).

Stern, S. Alan↗
NASA NTRS1999

Meteorites and the Evolution of Our Solar System

The study of meteorites has long been of intense interest ever since these objects were discovered to be of extraterrestrial origin. Meteorite research contributes to unraveling the mysteries in understanding the formation and evolution processes of our solar system. Meteorites, of which there are a variety of widely diverse types of chemical and mineralogical compositions, are the most ancient of solar system objects that can be studied in the laboratory. They preserve a unique historical record of the astronomical and astrophysical events of our solar system. This record is being discerned by a host of ever evolving analytical laboratory methods. Recent discoveries of what are believed to be Martian meteorites, lunar meteorites, a meteorite containing indigenous water, and the recovery from the Cretaceous layer of a small meteorite fragment thought to be from the dinosaur-killing asteroid have fueled additional excitement for studying meteorites.

Nava, David F.↗
NASA NTRS1985

Research on the Early History of the Solar System

The evolution of a dissipating turbulently viscous disk of gas and dust formed during the collapse of an interstellar cloud fragment and how it relates to the early history of the solar system is discussed. Results from calculations on modelling the inner parts of the primitive solar nebula subject to the assumption of a steady inward flow are given. Other calculations are reviewed which simulate the accretion of a star from an accretion disk. Scenarios for the evolution of the primitive solar nebula and the formation of the Moon as a result of a major collision with the protoearth are described.

Cameron, A. G. W.↗
NASA NTRS1986

Thermal histories, compositions and internal structures of the moons of the solar system

Thermal evolution models of satellites are discussed with emphasis placed on the fundamental physical processes common to all planetary bodies. A comparison is made between the different evolutionary tracks followed by individual satellites. Consideration is given to the compositions and structures of satellites, heat sources, relevant thermal and mechanical properties of the materials in satellite interiors, and heat transfer mechanisms. Thermal history scenarios are presented for the majority of the satellites of the solar system and these are related to the constraints imposed by surface geology.

Schubert, Gerald↗
NASA NTRS1992

1991 Urey Prize Lecture: Physical evolution in the solar system - Present observations as a key to the past

The present evaluation of the use of new observational methods for exploring solar system evolutionary processes gives attention to illustrative cases from the constraining of near-earth asteroid sources and the discovery of main-belt asteroid fragments which indicate Vesta to be a source of basaltic achondrite meteorites. The coupling of observational constraints with numerical models clarifies cratering and collisional evolution for both main-belt and Trojan asteroids.

Binzel, Richard P.↗
NASA NTRS1989

Chemical evolution of primitive solar system bodies

Observations on organic molecules and compounds containing biogenic elements in the interstellar medium and in the primitive bodies of the solar system are reviewed. The discovery of phosphorus molecular species in dense interstellar clouds, the existence of organic ions in the dust and gas phase of the comas of Comet Halley, and the presence of presolar, deuterium-hydrogen ratios in the amino acids of carbonaceous chondrites are discussed. The relationships between comets, dark asteroids, and carbonaceous chondrites are examined. Also, consideration is given to the chemical evolution of Titan, the primitive earth, and early Mars.

Oro, J.↗
NASA NTRS1983

Impact of solar system exploration on theories of chemical evolution and the origin of life

The impact of solar system exploration on theories regarding chemical evolution and the origin of life is examined in detail. Major findings from missions to Mercury, Venus, the moon, Mars, Jupiter, Saturn, and Titan are reviewed and implications for prebiotic chemistry are discussed. Among the major conclusions are: prebiotic chemistry is widespread throughout the solar system and universe; chemical evolution and the origin of life are intimately associated with the origin and evolution of the solar system; the rate, direction, and extent of prebiotic chemistry is highly dependent upon planetary characteristics; and continued exploration will increase understanding of how life originated on earth and allow better estimates of the likelihood of similar processes occurring elsewhere.

Devincenzi, D. L.↗
NASA NTRS2012

Using Schumann Resonance Measurements for Constraining the Water Abundance on the Giant Planets - Implications for the Solar System Formation

The formation and evolution of the Solar System is closely related to the abundance of volatiles, namely water, ammonia, and methane in the protoplanetary disk. Accurate measurement of volatiles in the Solar System is therefore important to understand not only the nebular hypothesis and origin of life but also planetary cosmogony as a whole. In this work, we propose a new, remote sensing technique to infer the outer planets water content by measuring Tremendously and Extremely Low Frequency (TLF-ELF) electromagnetic wave characteristics (Schumann resonances) excited by lightning in their gaseous envelopes. Schumann resonance detection can be potentially used for constraining the uncertainty of volatiles of the giant planets, mainly Uranus and Neptune, because such TLF-ELF wave signatures are closely related to the electric conductivity profile and water content.

Simoes, Fernando↗
NASA NTRS1973

The early evolution of the solar system

The problems of relating collapse conditions in an interstellar cloud to a model of the primitive solar nebula are discussed. In such a nebula there is a radial force balance between gravity, the pressure gradient, and centrifugal forces due to the rotation. Approximate values are given for the combinations of temperature and density throughout the nebula, from a maximum of about 2000 K near the center to less than 200 K in the outer portion. These conditions are based upon the compression adiabats in the terminal stages of the collapse of an interstellar cloud. One general conclusion, of great importance for accumulation of bodies within the solar system, is that interstellar grains should not be completely evaporated at distances in the nebula beyond about one or more astronomical units.

Cameron, A. G. W.↗
NASA NTRS2002

Dynamical Models of the Solar System Formation and Evolution

Mark Lewis has extended his them is work by completing a series of N-body simulations of a narrow ring that: is in the location of Saturn's F-ring and is perturbed by a single satellite comparable to Prometheus, but on a circular orbit. We had previously shown how the satellite perturbations can cause a broadly distributed sparse population of ring particles to become concentrated into narrow rings that can be maintained outside of any resonance location. For low optical depths, the collisions between ring particles are highly localized in the peaks of the satellite wakes. The inelastic collisions therefore occur at a particular orbital phase angle so as to damp the azimuthal component of the relative velocities. Since particle positions are not changed by collisions, the semimajor axes of the particles are shifted toward the actual particle positions where the collisions occur. Thus, negative radial diffusion can occur while conserving orbital angular momentum so long as the forced eccentricity is continually re-excited by the satellite. We speculated that the separation between the final ringlets was largely determined by the magnitude of the forced eccentricities induced by the satellite at closest approach. We carried out a series of simulations with a variety of different satellite masses in order to vary the magnitude of the forced eccentricity. We found that indeed the final spacing of the ringlets does increase with the magnitude of the forced eccentricity (Lewis and Stewart 2002). This occurs because neighboring eccentric ringlets drift out of phase with one another due to Keplerian shear and eventually collide with one another, leading to a smaller number of more widely spaced ringlets, The time scale required to form narrow ringlets in these simulations is much shorter than one would expect from standard theories based upon the orbit-averaged torque produced by multiple passes by the satellite. We find that the initial ringlets form in less than two synodic periods and the final state is typically reached in 10 to 20 synodic periods. These studies move us closer to understanding the significantly more complex system of Saturn's F ring, where the perturbation magnitude varies over short temporal and spatial time scales due to the orbital eccentricities of the perturbing satellite. We are currently extending the simulation to allow for an eccentric orbit of the satellite.

Stewart, Glen R.↗
NASA NTRS2013

Erosion, Transportation, and Deposition on Outer Solar System Satellites: Landform Evolution Modeling Studies

Mass movement and landform degradation reduces topographic relief by moving surface materials to a lower gravitational potential. In addition to the obvious role of gravity, abrasive mechanical erosion plays a role, often in combination with the lowering of cohesion, which allows disaggregation of the relief-forming material. The identification of specific landform types associated with mass movement and landform degradation provides information about local sediment particle size and abundance and transportation processes. Generally, mass movements can be classified in terms of the particle sizes of the transported material and the speed the material moved during transport. Most degradation on outer planet satellites appears consistent with sliding or slumping, impact erosion, and regolith evolution. Some satellites, such as Callisto and perhaps Hyperion and Iapetus, have an appearance that implies that some additional process is at work, most likely sublimation-driven landform modification and mass wasting. A variant on this process is thermally driven frost segregation as seen on all three icy Galilean satellites and perhaps elsewhere. Titan is unique among outer planet satellites in that Aeolian and fluvial processes also operate to erode, transport, and deposit material. We will evaluate the sequence and extent of various landform-modifying erosional and volatile redistribution processes that have shaped these icy satellites using a 3-D model that simulates the following surface and subsurface processes: 1) sublimation and re-condensation of volatiles; 2) development of refractory lag deposits; 3) disaggregation and downward sloughing of surficial material; 4) radiative heating/cooling of the surface (including reflection, emission, and shadowing by other surface elements); 5) thermal diffusion; and 6) vapor diffusion. The model will provide explicit simulations of landform development and thusly predicts the topographic and volatile evolution of the surface and final landscape form as constrained by DEMs. We have also simulated fluvial and lacustrine modification of icy satellites landscapes to evaluate the degree to which fluvial erosion of representative initial landscapes can replicate the present Titan landscape.

erosion↗
NASA NTRSDate not supplied

The Role of Isotopes in Understanding of the Formation and Evolution of the Solar System

Comparative planetology via isotope geochemistry has played a critical role in advancing our understanding of the inventories of both volatiles and organics in the atmospheres of solar system bodies. For example, the 12 C/ 13 C measured from atmospheric methane in Titan provided upper limits on the amount of time that methane has been present in the atmosphere, demonstrating that methane was only present in Titan’s atmosphere during at most the last 1 billion years (Gyr). As another example, measurements of 14 N/ 15 N in atmospheric HCN and N 2 provide direct evidence of how photochemistry influences stable isotopes. These observations were used to determine that Titan’s nitrogen originated as NH 3 in the protosolar nebula, thus constraining the origin and delivery of volatiles to the Saturnian moon Titan. These measurements of 12 C/ 13 C and 14 N/ 15 N in Titan’s atmosphere were obtained with remote and in situ observations from the Cassini spacecraft in Saturn orbit. However, combining spacecraft observations like these throughout the solar system with Earth-based telescope observations, including both ground-based and from orbiting telescopes, produces far more powerful results. For example, the lower limit obtained for 14 N/ 15 N in HCN in Pluto’s atmosphere by ALMA combined with New Horizons observations of the atmospheric composition provides a valuable tool for determining the origin of nitrogen for Pluto if the influences of condensation and aerosol trapping on isotopes can be constrained. Isotopes measured at Jupiter and Saturn and their moons, combined with composition measurements from comets provide information on giant planet formation processes and primordial conditions when the solar system was forming. In all of these studies, measurements of isotope ratios in comets have served as a reference for processes in the protosolar nebula.

Kathleen E. Mandt↗