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NASA NTRS2002

Atmospheres of the Giant Planets

The giant planets, Jupiter, Saturn, Uranus, and Neptune, are fluid objects. They have no solid surfaces because the light elements constituting them do not condense at solar-system temperatures. Instead, their deep atmospheres grade downward until the distinction between gas and liquid becomes meaningless. The preceding chapter delved into the hot, dark interiors of the Jovian planets. This one focuses on their atmospheres, especially the observable layers from the base of the clouds to the edge of space. These veneers arc only a few hundred kilometers thick, less than one percent of each planet's radius, but they exhibit an incredible variety of dynamic phenomena. The mixtures of elements in these outer layers resemble a cooled-down piece of the Sun. Clouds precipitate out of this gaseous soup in a variety of colors. The cloud patterns are organized by winds, which are powered by heat derived from sunlight (as on Earth) and by internal heat left over from planetary formation. Thus the atmospheres of the Jovian planets are distinctly different both compositionally and dynamically from those of the terrestrial planets. Such differences make them fascinating objects for study, providing clues about the origin and evolution of the planets and the formation of the solar system.

Ingersoll, Andrew P.↗
NASA NTRS2022

A Deep and Wide Twilight Survey for Asteroids Interior to Earth and Venus

We are conducting a survey using twilight time on the Dark Energy Camera with the Blanco 4 m telescope in Chile to look for objects interior to Earth's and Venus' orbits. To date we have discovered two rare Atira/Apohele asteroids, 2021 LJ4 and 2021 PH27, which have orbits completely interior to Earth's orbit. We also discovered one new Apollo-type Near Earth Object (NEO) that crosses Earth's orbit, 2022 AP7. Two of the discoveries have diameters ≳1 km. 2022 AP7 is likely the largest Potentially Hazardous Asteroid (PHA) discovered in about eight years. To date we have covered 624 square degrees of sky near to and interior to the orbit of Venus. The average images go to 21.3 mag in the *r* band, with the best images near 22nd mag. Our new discovery 2021 PH27 has the smallest semimajor axis known for an asteroid, 0.4617 au, and the largest general relativistic effects (53 arcsec/century) known for any body in the solar system. The survey has detected ∼15% of all known Atira NEOs. We put strong constraints on any stable population of Venus co-orbital resonance objects existing, as well as the Atira and Vatira asteroid classes. These interior asteroid populations are important to complete the census of asteroids near Earth, including some of the most likely Earth impactors that cannot easily be discovered in other surveys. Comparing the actual population of asteroids found interior to Earth and Venus with those predicted to exist by extrapolating from the known population exterior to Earth is important to better understand the origin, composition, and structure of the NEO population.

Scott S. Sheppard↗
DOE OSTI2021

Evaluation of Interior Cellular Shades in a Residential Building

Windows are major contributors to energy demand in residential homes because of their inferior thermal resistance compared with the opaque envelope and sometimes from unwanted solar heat gain. Window attachments can help to mitigate this demand by controlling the solar heat gains and enhancing the thermal resistance of the windows. In this study, the energy savings potential of cellular shades in residential homes is studied using experimental testing and energy simulations. The energy performance of the shading devices was experimentally tested during the heating season from December 2019 to May 2020 with a focus on cellular shades. Five shading devices—three single and two double cellular/cell-in-cell shades—were used to compare the performance with generic horizontal (venetian) blinds using two nearly identical sideby-side rooms in a residential building with their exterior window facing east. Another objective of the experimental testing was to evaluate any impact of the side-channel of the shading device on energy savings. To observe the impact of the side-channels on energy savings, from shades in two of the test cases, cellular shades with side-channels were used. From the experimental testing, daily energy savings in the range of 9% to 23% were observed by considering data from 6 p.m. until 6 a.m. of the next day.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
NASA NTRS1976

The EUV chromospheric network in the quiet sun

Investigations on the structure and intensity of the chromospheric network from quiet solar regions have been carried out with EUV data obtained with a spectroheliometer on the Apollo Telescope Mount of Skylab. The distribution of intensities within supergranulation cell interiors follows a near-normal function, where the standard deviation exceeds the value expected from the counting rate, which indicates fine-scale structure below the 5 arcsec resolution of the data. The intensities from the centers of supergranulation cells appear to be the same in both quiet regions and coronal holes, although the network is significantly different in the two types of regions. The average halfwidth of the network elements was measured as 10 arcsec and was independent of the temperature of formation of the observing line for effective-temperature logarithms (log Te) from 3.8 to 5.8. The contrast between the network and the centers of cells is greatest for lines with log Te about equal to 5.2, where the network contributes approximately 75% of the intensity of quiet solar regions. The contrast and fractional-intensity contributions decrease to higher and lower temperatures characteristic of the corona and chromosphere.

Reeves, E. M.↗
NASA NTRS2009

Proceedings of the 40th Lunar and Planetary Science Conference

The 40th Lunar and Planetary Science Conference included sessions on: Phoenix: Exploration of the Martian Arctic; Origin and Early Evolution of the Moon; Comet Wild 2: Mineralogy and More; Astrobiology: Meteorites, Microbes, Hydrous Habitats, and Irradiated Ices; Phoenix: Soil, Chemistry, and Habitability; Planetary Differentiation; Presolar Grains: Structures and Origins; SPECIAL SESSION: Venus Atmosphere: Venus Express and Future Missions; Mars Polar Caps: Past and Present; SPECIAL SESSION: Lunar Missions: Results from Kaguya, Chang'e-1, and Chandrayaan-1, Part I; 5 Early Nebula Processes and Models; SPECIAL SESSION: Icy Satellites of Jupiter and Saturn: Cosmic Gymnasts; Mars: Ground Ice and Climate Change; SPECIAL SESSION: Lunar Missions: Results from Kaguya, Chang'e-1, and Chandrayaan-1, Part II; Chondrite Parent-Body Processes; SPECIAL SESSION: Icy Satellites of Jupiter and Saturn: Salubrious Surfaces; SNC Meteorites; Ancient Martian Crust: Primary Mineralogy and Aqueous Alteration; SPECIAL SESSION: Messenger at Mercury: A Global Perspective on the Innermost Planet; CAIs and Chondrules: Records of Early Solar System Processes; Small Bodies: Shapes of Things to Come; Sulfur on Mars: Rocks, Soils, and Cycling Processes; Mercury: Evolution and Tectonics; Venus Geology, Volcanism, Tectonics, and Resurfacing; Asteroid-Meteorite Connections; Impacts I: Models and Experiments; Solar Wind and Genesis: Measurements and Interpretation; Mars: Aqueous Processes; Magmatic Volatiles and Eruptive Conditions of Lunar Basalts; Comparative Planetology; Interstellar Matter: Origins and Relationships; Impacts II: Craters and Ejecta Mars: Tectonics and Dynamics; Mars Analogs I: Geological; Exploring the Diversity of Lunar Lithologies with Sample Analyses and Remote Sensing; Chondrite Accretion and Early History; Science Instruments for the Mars Science Lander; . Martian Gullies: Morphology and Origins; Mars: Dunes, Dust, and Wind; Mars: Volcanism; Early Solar System Chronology; Seek Out and Explore: Upcoming and Future Missions; Mars: Early History and Impact Processes; Mars Analogs II: Chemical and Spectral; Achondrites and their Parent Bodies; and Planning for Future Exploration of the Moon The poster sessions were: Lunar Missions: Results from Kaguya, Chang'e-1, and Chandrayaan-1; LRO and LCROSS; Geophysical Analysis of the Lunar Surface and Interior; Remote Observation and Geologic Mapping of the Lunar Surface; Lunar Spectroscopy; Venus Geology, Geophysics, Mapping, and Sampling; Planetary Differentiation; Bunburra and Buzzard Coulee: Recent Meteorite Falls; Meteorites: Terrestrial History; CAIs and Chondrules: Records of Early Solar System Processes; Volatile and Organic Compounds in Chondrites; Crashing Chondrites: Impact, Shock, and Melting; Ureilite Studies; Petrology and Mineralogy of the SNC Meteorites; Martian Meteorites; Phoenix Landing Site: Perchlorate and Other Tasty Treats; Mars Polar Atmospheres and Climate Modeling; Mars Polar Investigations; Mars Near-Surface Ice; Mars: A Volatile-Rich Planet; Mars: Geochemistry and Alteration Processes; Martian Phyllosilicates: Identification, Formation, and Alteration; Astrobiology; Instrument Concepts, Systems, and Probes for Investigating Rocks and Regolith; Seeing is Believing: UV, VIS, IR, X- and Gamma-Ray Camera and Spectrometer Instruments; Up Close and Personal: In Situ Analysis with Laser-Induced Breakdown Spectroscopy and Mass Spectrometry; Jupiter and Inscrutable Io; Tantalizing Titan; Enigmatic Enceladus and Intriguing Iapetus; Icy Satellites: Cryptic Craters; Icy Satellites: Gelid Geology/Geophysics; Icy Satellites: Cool Chemistry and Spectacular Spectroscopy; Asteroids and Comets; Comet Wild 2: Mineralogy and More; Hypervelocity Impacts: Stardust Models, LDEF, and ISPE; Presolar Grains; Early Nebular Processes: Models and Isotopes; Solar Wind and Genesis: Measurements and Interpretation; Education and Public Outreach; Mercury; Pursuing Lunar Exploration; Sources and Eruptionf Lunar Basalts; Chemical and Physical Properties of the Lunar Regolith; Lunar Dust and Transient Surface Phenomena; Lunar Databases and Data Restoration; Meteoritic Samples of the Moon; Chondrites, Their Clasts, and Alteration; Achondrites: Primitive and Not So Primitive; Iron Meteorites; Meteorite Methodology; Antarctic Micrometeorites; HEDs and Vesta; Dust Formation and Transformation; Interstellar Organic Matter; Early Solar System Chronology; Comparative Planetology; Impacts I: Models and Experiments; Impacts II: Craters and Ejecta; Mars: Volcanism; Mars: Tectonics and Dynamics; Martian Stratigraphy: Understanding the Geologic History of Mars Through the Sedimentary Rock Record; Mars: Valleys and Valley Networks; Mars: Aqueous Processes in Valles Marineris and the Southern Highlands; Mars: Aqueous Geomorphology; Martian Gullies: Morphology and Origins; Mars: Dunes, Dust, and Wind; Mars: Remote Sensing; Mars: Geologic Mapping, Photogrammetry, and Cratering; Martian Mineralogy: Constraints from Missions and Laboratory Investigations; Mars Analogs: Chemical and Physical; Mars Analogs: Sulfates and Sulfides; Missions: Approaches, Architectures, Analogs, and Actualities; Not Just Skin Deep: Electron Microscopy, Heat Flow, Radar, and Seismology Instruments and Planetary Data Systems, Techniques, and Interpretation.

Source record↗
NASA NTRS2002

A Solar System Perspective on Laboratory Astrophysics

Planetary science deals with a wide variety of natural materials in a wide variety of environments. These materials include metals, minerals, ices, gases, plasmas, and organic chemicals. In addition, the newly defined discipline of astrobiology introduces biological materials to planetary science. The environments range from the interiors of planets with megapascal pressures to planetary magnetospheres, encompassing planetary mantles, surfaces, atmospheres, and ionospheres. The interplanetary environment includes magnetic and electrical fields, plasma, and dust. In order to understand planetary processes over these vast ranges, the properties of materials must be known, and most of the necessary information comes from the laboratory. Observations of the bodies and materials in the Solar System are accomplished over the full range of the electromagnetic spectrum by remote sensing from Earth or spacecraft. Comets exemplify this; molecular and atomic identifications are made from the hard ultraviolet to radio wavelengths, while X-rays are emitted as comets interact with the solar wind. Gamma rays from the surfaces of the Moon and asteroids are diagnostic of the mineral and ice content of those bodies; eventually, gamma rays will also be observed by probes to comets. A number of planetary materials are available in the laboratory for extensive Study: rocks from the Moon, Mars, several asteroids, as well as dust from comets (and perhaps the Kuiper Belt) are closely studied at every level, including atomic (isotopic). Even pre-solar interstellar grains isolated from meteorites are scrutinized for composition and crystalline structure. Beyond the materials themselves, various agents and processes have altered them over the 4.6-Gy age of the Solar System. Solar radiation, solar wind particles, trapped magnetospheric particles, cosmic rays, and micrometeoroid impacts have produced chemical, physical, and morphological changes in the atmospheres and on the surfaces of all planetary bodies. These processes are not well understood, so studies in a laboratory setting are especially needed.

Cruikshank, Dale P.↗
NASA NTRS1971

Lunar magnetic field measurements, electrical conductivity calculations and thermal profile inferences

Steady magnetic field measurements of magnitude 30 to 100 gamma on the lunar surface impose problems of interpretation when coupled with the nondetectability of a lunar field at 0.4 lunar radius altitude and the limb induced perturbations of the solar wind at the Explorer orbit. The lunar time-varying magnetic field clearly indicates the presence of eddy currents in the lunar interior and permits calculation of an electrical conductivity profile. The problem is complicated by the day-night asymmetry of the moon's electromagnetic environment, the possible presence of the transverse magnetic mode, and the variable wave directions of the driving function. The electrical conductivity is calculated to be low near the surface, rising to a peak of .006/ohm meter at 250 km, dropping steeply inwards to a value of about .00005/ohm meter, and then rising toward the interior. A transition at 250 km depth from a high conductivity to a low conductivity material is inferred, suggesting an olivine-like core at approximately 800 C, although other models are possible.

Colburn, D. S.↗
NASA NTRS1984

Structure of ices on satellites

The pressure densification of ices, in combination with density changes induced by pore migration in a thermal gradient and the phase transitions of water due to meteoritic bombardment (into either high pressure polymorphs or an amorphous phase) create a complex situation, which is not easily evaluated in either satellites or cometary nuclei. Accordingly, the present findings concerning solar system satellites and comets cannot be rendered quantitative. In general, due to insolation, icy satellites may have slightly warmer surfaces than their interiors. If there are CO2 ice inclusions in satellite water ices, they would have diffused as vapor along pores toward the cold interiors or, if near the surface, would have evaporated. The presence of pores and amorphous ice in cometary nuclei has an important effect on their flare-up and the size of the comas and tails.

Smoluchowski, R.↗
NASA NTRS2006

Direct Imaging of Stellar Surfaces: Results from the Stellar Imager (SI) Vision Mission Study

The Stellar Imager (SI) is a UV-Optical, Space-Based Interferometer designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and stellar interiors (via asteroseismology) and of the Universe in general. SI is identified as a "Flagship and Landmark Discovery Mission'' in the 2005 Sun Solar System Connection (SSSC) Roadmap and as a candidate for a "Pathways to Life Observatory'' in the Exploration of the Universe Division (EUD) Roadmap (May, 2005). The ultra-sharp images of the Stellar Imager will revolutionize our view of many dynamic astrophysical processes: The 0.1 mas resolution of this deep-space telescope will transform point sources into extended sources, and snapshots into evolving views. SI's science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI's prime goal is to enable long-term forecasting of solar activity and the space weather that it drives in support of the Living With a Star program in the Exploration Era. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. In this paper we will discuss the results of the SI Vision Mission Study, elaborating on the science goals of the SI Mission and a mission architecture that could meet those goals.

Carpenter, Kenneth↗
NASA NTRS2006

Stellar Imager (SI) Space Mission: Stellar Magnetic Activity

The Stellar Imager (SI) is a UV-Optical, Space-Based interferometer designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and stellar interiors (via asteroseismology) and of the Universe in general. SI is identified as a "Flagship and Landmark Discovery Mission" in the 2005 Sun Solar System Connection (SSSC) Roadmap and as a candidate for a "Pathways to Life Observatory" in the Exploration of the Universe Division (EUD) Roadmap (May, 2005). The ultra-sharp images of the Stellar Imager will revolutionize our view of many dynamic astrophysical processes: The 0.1 mas resolution of this deep-space telescope will transform point sources into extended sources, and snapshots into evolving views. SI'S science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI'S prime goal is to enable long-term forecasting of solar activity and the space weather that it drives in support of the Living With a Star program in the Exploration Era. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. In this paper we will discuss the science goals of the SI Mission and a mission architecture that could meet those goals.

Carpenter, K. G.↗
NASA NTRS2023

Delayed Development of Cool Plasmas in X-Ray Flares from the Young Sun-like Star κ1 Ceti

The Neutron star Interior Composition Explorer (NICER) X-ray observatory observed two powerful X-ray flares equivalent to superflares from the nearby young solar-like star κ 1 Ceti in 2019. NICER follows each flare from the onset through the early decay, collecting over 30 counts s −1 near the peak, enabling a detailed spectral variation study of the flare rise. The flare in September varies quickly in ∼800 s, while the flare in December has a few times longer timescale. In both flares, the hard-band (2–4 keV) light curves show typical stellar X-ray flare variations with a rapid rise and slow decay, while the soft X-ray light curves, especially of the September flare, have prolonged flat peaks. The time-resolved spectra require two temperature plasma components at kT ∼0.3–1 and ∼2–4 keV. Both components vary similarly, but the cool component lags by ∼200 s with a four to six times smaller emission measure (EM) compared to the hot component. A comparison with hydrodynamic flare loop simulations indicates that the cool component originates from X-ray plasma near the magnetic loop footpoints that mainly cools via thermal conduction. The time lag represents the travel time of the evaporated gas through the entire flare loop. The cool component has a several times smaller EM than its simulated counterpart, suggesting a suppression of conductive cooling, possibly by the expansion of the loop cross-sectional area or turbulent fluctuations. The cool component's time lag and EM ratio provide important constraints on the flare loop geometry.

main sequence stars↗
NASA NTRS1999

Thermally Mobile Trace Elements in Carbonaceous Chondrites from Cold and Hot Deserts

Some decades ago, Anders and co-workers used RNAA to classify a number of trace elements as being volatile during nebular condensation and accretion into primitive objects based upon their strong depletion in (equilibrated) ordinary chondrites relative to C1 chondrites. Such elements, e.g. Ag, Bi, Cd, Cs, In, Se, Te, Tl, Zn and others, exhibit nearly constant, C1-normalized atomic abundances in C2 (CM2) and in C3 chondrites. They interpreted the near-constancy of these abundances according to a 2-component model in which volatiles were introduced into carbonaceous (and other) chondrites as Cl material which was diluted with differing proportions of high-temperature (i.e. volatile-free) components. In this view, mean volatile element abundances of 0.48 in C2 and 0.24-0.29 x C1 in C3 chondrites indicated that C2 and C3 chondrites are, respectively, about 1:1 and 1:2-3 mixtures of Cl-like and high temperature materials. More recently, C1 normalized abundances of such volatile elements are nearly constant in most C2-6 chondrites (i.e. 25 non-Antarctic meteorites, nearly all falls, and 36 Antarctic finds) consistent with a 2- component mixing model. However, rather than being quantized, mean volatile element contents in each chondrite define a continuum from 0.92-0.14 x Cl for these 61 chondrites. A few carbonaceous chondrites - the first having been the NIPR consortium samples B-7904, Y-82162 and Y-86720 - show an altered pattern: many of the volatile elements in each exhibit the usual constancy of C1-normalized atomic abundances, but modified by further depletion of Cd and other elements like Tl and Bi. These are the most mobile trace elements, i.e. those most readily vaporized and lost from primitive meteorites during week-long heating at greater than or equal to 400 C under low ambient pressures (initially 10 (exp -5) atm H2), simulating metamorphic conditions in a primitive parent body. Similarities between mobile element data for B-7904, Y-82162 and Y-86720 with those for Murchison heated at 500-700 C suggest that these Antarctic C1 and C2-like chondrites were metamorphosed at temperatures like these in the interiors of their parent bodies. Metamorphic temperatures inferred from RNAA data and textural/mineralogic alterations are internally consistent, agreeing with those evident in heated Murchison samples. These 3 chondrites were also heated late in their histories since all have lost cosmogenic 3-He, presumably during close solar approach, and B-7904 and Y-86720 seem also to have lost substantial proportions of radiogenic He-4 and Ar-40, cf. data. Similarities in spectral reflectance data for C-, G-, B- and F- asteroids, for these meteorites and for heated Murchison samples suggest that thermally metamorphosed interior materials in these asteroids were excavated by impacts and re-deposited on them, forming their present surfaces. Establishment of the thermal metamorphic histories of carbonaceouis chondrites, then, is essential to establishing the evolution and present-day nature of C-type and related asteroids.

Lipschutz, M. E.↗
NASA NTRS2000

Thermally Mobile Trace Elements in Carbonaceous Chondrites From Cold and Hot Deserts

Some decades ago, Anders and co-workers used RNAA to classify a number of trace elements as being volatile during nebular condensation and accretion into primitive objects based upon their strong depletion in (equilibrated) ordinary chondrites relative to C1 chondrites. Such elements, e.g. Ag, Bi, Cd, Cs, In, Se, Te, Tl, Zn and others, exhibit nearly constant, C1-normalized atomic abundances in C2 (CM2) and in C3 chondrites. They interpreted the near-constancy of these abundances according to a 2-component model in which volatiles were introduced into carbonaceous (and other) chondrites as C1 material which was diluted with differing proportions of high-temperature (i.e. volatile-free) components. In this view, mean volatile element abundances of 0.48 in C2 and 0.24-0.29 x C1 in C3 chondrites indicated that C2 and C3 chondrites are, respectively, about 1:1 and 1:2-3 mixtures of C1-like and high temperature materials. More recently, Xiao and Lipschutz found that C-normalized abundances of such volatile elements are nearly constant in most C2-6 chondrites (i.e. 25 non-Antarctic meteorites, nearly all falls, and 36 Antarctic finds) consistent with a 2-component mixing model. However, rather than being quantized, mean volatile element contents in each chondrite define a continuum from 0.92-0.14 x C1 for these 61 chondrites. A few carbonaceous chondrites, the first having been the NIPR consortium samples B-7904, Y-82162 and Y-86720, show an altered pattern: many of the volatile elements in each exhibit the usual constancy of C1-normalized atomic abundances, but modified by further depletion of Cd and other elements like Tl and Bi. These are the most mobile trace elements, i.e. those most readily vaporized and lost from primitive meteorites during week-long heating at greater than or equal to 400 C under low ambient pressures (initially 10(exp -5) atm H2), simulating metamorphic conditions in a primitive parent body. Similarities between mobile element data for B-7904, Y-82162 and Y-86720 with those for Murchison heated at 500-700 C, suggest that these Antarctic C1 - and C2-like chondrites were metamorphosed at temperatures like these in the interiors of their parent bodies. Metamorphic temperatures inferred from RNAA data and textural/mineralogic alterations are internally consistent, agreeing., with those evident in heated Murchison samples. These 3 chondrites were also heated late in their histories since all have lost cosmogenic He-3, presumably during close solar approach, and B-7904 and Y-86720 seem also to have lost substantial proportions of radiogenic He-4 and Ar-40 cf. data in. Similarities in spectral reflectance data for C-, G-, B- and F- asteroids, for these meteorites and for heated Murchison samples suggest that thermally metamorphosed interior materials in these asteroids were excavated by impacts and re-deposited on them, forming their present surfaces. Establishment of the thermal metamorphic histories of carbonaceous chondrites, then, is essential to establishing the evolution and present-day nature of C-type and related asteroids.

Lipschutz, M. E.↗
NASA NTRS2022

Titan In-situ Resource Utilization (ISRU) Sample Return (TISR)

Titan is unique in the outer solar system in that it is the only moon with a thick atmosphere, and the only body in the solar system outside the Earth with liquid seas on its surface. The Titanian oceans, however, are seas of liquid hydrocarbons, and the rocks on the surface are solid water ice. Like other icy Moons of the outer solar system, beneath the ice crust, Titan also has a subsurface ocean. Rodriguez et al. refer to it as the “world with two oceans”, an organic-rich body with interior-surface-atmosphere interactions that are comparable in complexity to the Earth. [1] Titan is scientifically fascinating in many ways [2], [3], [4]. The Compass Team will emphasize just one here: Titan is a high priority target for astrobiology [4] [5] [6] [7] [8] [9] [10] [11]. It is a world with a surface and atmosphere rich in the complex organic compounds known as tholins. A detailed understanding of the nature of these complex compounds will require an analysis using a full laboratory on Earth. Because of its value to understanding the organic compounds of the outer solar system which may be the primordial building-blocks of life, return of samples from Titan to laboratories on Earth will be the primary goal of this mission. While this would give unprecedented science return, returning even a small sample from Titan using conventional technology would be tremendously difficult. Saturn is almost a billion miles from the Earth, about thirteen times farther than Mars. A return mission to Saturn requires such a large total-mission ∆V that, with conventional technology, the mass ratios required are prohibitive. Such a sample return would truly be “mission incredible.” But to date, a sample return mission from so distant a target has been assumed to be, not merely incredible, but mission impossible. The Compass Team has proposed [2] [12] that by manufacturing the propellant for the return to Earth using the resources available on Titan, such a mission becomes possible. The task of this report is to show that it is reasonable with credible space technology.

Titan↗
NASA NTRS2003

The Galileo Probe: How it Has Changed Our Understanding of Jupiter

The Galileo Mission to Jupiter, which arrived in December of 1995, provided the first study by an orbiter, and the first in-situ sampling via an entry probe, of an outer planet atmosphere. The rationale for an entry probe is that, even from an orbiter, remote sensing of the jovian atmosphere could not adequately retrieve the information desired. This paper provides a current summary of the most significant aspects of the data returned from the Galileo entry probe. As a result of the probe measurements, there has been a reassessment of our understanding of outer planet formation and evolution of the solar system. The primary scientific objective of the Galileo probe was to determine the composition of the jovian atmosphere, which from remote sensing remained either very uncertain, or completely unknown, with respect to several key elements. The probe found that the global He mass fraction is. significantly above the value reported from the Voyager Jupiter flybys but is slightly below the protosolar value, implying that there has been some settling of He to the deep jovian interior. The probe He measurements have also led to a reevaluation of the Voyager He mass fraction for Saturn, which is now determined to be much closer to that of Jupiter. The elements C, N, S, Ar, Kr, Xe were all found to have global abundances approximately 3 times their respective solar abundances. This result has raised a number of fundamental issues with regard to properties of planetesimals and the solar nebula at the time of giant planet formation. Ne, on the other hand, was found to be highly depleted, probably as the result of it being carried along with helium as helium settles towards the deep interior. The global abundance of O was not obtained by the probe because of the influence of local processes at the probe entry site (PES), processes which depleted condensible species, in this case H2O, well below condensation levels. Other condensible species, namely NH3 and H2S, were similarly affected but attained their deep equilibrium mixing ratios before the maximum depth sampled by the probe. Processes that might be capable of producing such effects on the condensibles are still under investigation. Measured isotopic ratios of noble gases and other heavy elements are solar, and (D + (Sup 3)He)/H is the same to within measurement uncertainties as in the local interstellar medium. No thick clouds were detected, and in particular no significant water cloud, but the PES location clearly affected the probe measurements of clouds. In fact, the probe data must be understood in the context of the location of the PES, which was within what is termed a 5 micron hot spot, a local clearing in the clouds that is bright near the 5 microns spectral region. The thermal structure at the PES was determined from approximately 1000 km above the 1 bar pressure level (10(exp -9 bars)) to 132 km 1 bar (22bars). The probe showed the atmosphere to have a generally sub-adiabatic temperature gradient (static stability) of = 0.1 K/km to as deep as the probe made measurements. In the upper atmosphere the probe derived a maximum positive vertical temperature gradient of approximately 5 K/km, and maximum temperature of = 900 K. The energy sources producing the warm upper atmosphere have yet to be completely identified. At first glance, Doppler tracking of the probe indicates that the long observed cloud level zonal winds extend to levels at least as deep as the probe made measurements. Zonal wind increases from = 80 m/s at pressures less than a bar to about 180 m/s near 5 bars, and remains approximately constant with depth thereafter. However, there is a question as to whether the winds measured from probe tracking are representative of the general wind field, or are considerably influenced by localized winds associated with the PES.

Young, Richard E.↗
NASA NTRS1978

Mariner 10 magnetic field observations of the Venus wake

The paper reports on an analysis of magnetic field observations by the Mariner 10 spacecraft during approximately a one-day period ending a few hours beyond Venus encounter on February 5, 1974. The magnetic field measurements are used to study the downstream region of the solar wind-Venus interaction over a distance of about 100 Venus radii. The study characterizes the various magnetic field regions encountered behind and near the planet; presents an argument that the magnetic field signatures observed are consistent with observation of either a steady or a transient wake, or at least the boundary region of such a wake, interior to a common sheath-like region; examines in detail the fluctuation and discontinuity features of these regions and compares them with those of the interplanetary medium; and summarizes how these new features contribute to the understanding of the solar wind-Venus interaction.

Lepping, R. P.↗
NASA NTRS1991

Modeling the surface and interior structure of comet nuclei using a multidisciplinary approach

The goal was to investigate the structural properties of the surface of comet nucleus and how the surface should change with time under effect of solar radiation. The basic model that was adopted was that the nucleus is an aggregate of frosty particles loosely bound together, so that it is essentially a soil. The nucleus must mostly be composed of dust particles. The observed mass ratios of dust to gas in the coma is never much greater than unity, but this ratio is probably a much lower limit than that of the nucleus because it is vastly easier to remove the gaseous component by sublimation than by carrying off the dust. Therefore the described models assumed that the particles in the soil were frost covered grains of submicron basic size, closely resembling the interstellar grains. The surface properties of such a nucleus under the effects of heating and cooling as the nucleus approaches and recedes from the Sun generally characterized.

Odell, C. R.↗
NASA NTRS1983

Radioactivites in returned lunar materials and in meteorites

The cosmic-ray, solar-flare, and solar-wind bombardments of lunar rocks and soils and meteorites were studied by measurements of tritium, carbon-14 and argon radioactivity. The radioactivity integrates the bombardment for a time period equal to several half-lines. H-3, Ar-37, Ar-39, C-14. For the interior samples of lunar rocks and for deep lunar soil samples, the amounts of the radioactivities were equal to those calculated for galactic cosmic-ray interactions. The top near-surface samples of lunar rocks and the shallow lunar soil samples show excess amounts of the radioactivities attributable to solar flares. Lunar soil fines contain a large amount of hydrogen due to implanted solar wind. Studies of the H-3 in lunar soils and in recovered Surveyor-3 materials gave an upper limit for the H-3/H ratio in the solar wind of 10 to the -11th power. Solar wind carbon is also implanted on lunar soil fines. Lunar soils collected on the surface contained a 0.14 component attributable to implanted solar wind C-14. The C-14/H ratio attributed to the solar wind from this C-14 excess is approximately 4 x 10 to the -11th power.

Fireman, E. L.↗