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NASA NTRS2015

Strong Water Isotopic Anomalies in the Martian Atmosphere: Probing Current and Ancient Reservoirs

We measured maps of atmospheric water (H2O) and its deuterated form (HDO) across the martian globe, showing strong isotopic anomalies and a significant high deuterium/hydrogen (D/H) enrichment indicative of great water loss. The maps sample the evolution of sublimation from the north polar cap, revealing that the released water has a representative D/H value enriched by a factor of about 7 relative to Earth's ocean [Vienna standard mean ocean water (VSMOW)]. Certain basins and orographic depressions show even higher enrichment, whereas high-altitude regions show much lower values (1 to 3 VSMOW). Our atmospheric maps indicate that water ice in the polar reservoirs is enriched in deuterium to at least 8 VSMOW, which would mean that early Mars (4.5 billion years ago) had a global equivalent water layer at least 137 meters deep.

Research Support, U.S. Gov't, Non-P.H.S.↗

NASA NTRSDate not supplied

Control Algorithms for Flap-Based Mars Entry Systems

All guided entries of blunt-body entry vehicles have utilized bank-angle steering for hypersonic trajectory control. While bank-angle steering has been suc- cessful on Mars entry missions thus far, such as the Mars Science Laboratory and Mars 2020 missions, this control scheme involves a high degree of coupling over the longitudinal and lateral motion. To simultaneously control these two directions of flight, bank-angle steering vehicles typically select the bank angle magnitude to control the longitudinal motion and perform periodic bank reversals to limit the error in the lateral direction. These bank reversals are undesirable as they are performed open loop and can inject error into the trajectory. An alternative hypersonic control scheme modules the vehicle’s angle of attack (α) and sideslip angle (β) to steer the vehicle, i.e. α − β steering. Also called direct force control (DFC), α − β steering has been recently studied in the literature for both entry and aerocapture missions at several planetary bodies including Mars, Venus, Titan, and the ice giants. α − β steering provides more decoupled control over the trajectory than bank-angle steering by mostly using α to control the longitudinal motion and mostly using β to control the lateral motion. Using α − β steering avoids the bank reversals associated with bank-angle steering, and studies have shown that α − β steering may provide increased robustness to atmospheric dispersions, higher precision in landing accuracy, a lower propellant usage for powered descent, and a larger payload mass, relative to bank-angle steering. Several different actuation concepts have been studied for α − β steering, including moving mass systems, a morphing vehicle structure, and aerodynamic flaps.

Daniel L Engel↗

NASA NTRS1985

Application of shock wave data to earth and planetary science

It is pointed out that shock wave data for: (1) low temperature condensable gases H2 and He, (2) H2O, CH4, NH3, CO, CO2, and N2 ices, and (3) silicates, metals, oxides and sulfides have many applications in geophysics and planetary science. The present paper is concerned with such applications. The composition of planetary interiors is discussed, taking into account the division of the major constituent of the planets in three groups on the basis of 'cosmic abundance' arguments, the H-He mixtures in the case of Jupiter and Saturn, shock wave data for hydrogen, and constraints on the internal structure of Uranus and Neptune. Attention is also given to the earth's mantle, shock wave data for mantle materials, the earth's core, impacts on planetary surfaces, elastic wave velocities as a function of pressure along the Hugoniot of iron, and reactions which yield the CO2 bearing atmospheres for Venus, earth, and Mars.

Ahrens, T. J.↗

NASA NTRS1994

Mars together and FIRE and ICE: Report of the joint US/Russian technical working groups

The Cold War's end opened an opportunity for greater cooperation in planetary exploration for the United States and Russia. Two study groups were formed, Mars Together and FIRE and ICE. The Mars Together team developed a concept for a flight in 1998 that merged one U.S. Mars Surveyor 98 mission with the former Russian Mars 96 mission to further understanding of the Mars surface and atmosphere. The FIRE and ICE team developed concepts for a dual-spacecraft mission to the solar corona and for a mission to Pluto. The missions, scientific potential, and open issues are described.

Source record↗

NASA NTRS1994

A Mars Pathfinder landing on a recently drained ephemeral sea: Cerberus Plains, 6 deg N, 188 deg W

Along a 500 km-wide belt extending between 202 deg and 180 deg W and lying astride the martian equator, moderately low-albedo, uncratered smooth plains exhibit low thermal inertia and potentially favorable conditions for the preservation of near-surface ice. The Cerberus Plains occupy a topographic trough as much as 2 km below the planetary datum, and the denser atmosphere at these altitudes would also favor long residence times for near-surface ice once emplaced. The plains have previously been interpreted as the result of young (late Amazonian) low viscosity lava flows or similarly youthful fluvial deposition. However, the plains are also included in maps of possibly extensive martian paleoseas or paleolakes. Ice emplaced as such seas dissipated could still be preserved under thin (a few tens of centimeters) sedimentary cover. In any case, and if a sea once existed, aqueous-born interstitial cementation, probably including hydrated iron oxides and sulfate minerals, would have been favored and is now susceptible to investigation by the Pathfinder alpha proton x-ray spectrometer and multispectral imager.

Brakenridge, G. Robert↗

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 NTRS1984

Interior structure of Uranus

Key measurements are discussed which are diagnostic of Uranus' interior structure and evolutionary history, and reviews their present status. Typical interior models have chondritic cores, but have the bulk of their mass in an envelope consisting of ice component, principally H2O. The total amount of free H2 in the planet cannot exceed approximately 1 to 2 earth masses. Measurements of the gravitational moments of Uranus are beginning to be accurate enough to constrain models, but are limited in utility by uncertainty in the rotation period. Discussed is evidence that the outermost planetary layers have a gravitationally significant quantity of denser material (ice component?) in addition to H2 and He. The He/H ratio and the deuterium abundance in the atmosphere may be diagnostic of the planet's previous evolutionary history. It is argued that the planet's interior is likely to now be at a temperature approximately 10(3) deg K. Uranus' interior with Neptune's in a number of ways, considering heat flow, degree of internal differentiation, and possible magnetic field.

Hubbard, W. B.↗

NASA NTRS1993

Magnetic fields of the outer planets

It is difficult to imagine a group of planetary dynamos more diverse than those visited by the Pioneer and Voyager spacecraft. The magnetic field of Jupiter is large in magnitude and has a dipole axis within 10 deg of its rotation axis, comfortably consistent with the paleomagnetic history of the geodynamo. Saturn's remarkable (zonal harmonic) magnetic field has an axis of symmetry that is indistinguishable from its rotation axis (mush less than 1 deg angular separation); it is also highly antisymmetric with respect to the equator plane. According to one hypothesis, the spin symmetry may arise from the differential rotation of an electrically conducting and stably stratified layer above the dynamo. The magnetic fields of Uranus and Neptune are very much alike, and equally unlike those of the other known magnetized planets. These two planets are characterized by a large dipole tilts (59 deg and 47 deg, respectively) and quadrupole moments (Schmidt-normalized quadrupole/dipole ratio approximately equal 1.0). These properties may be characteristic of dynamo generation in the relatively poorly conducting 'ice' interiors of Uranus and Neptune. Characteristics of these planetary magnetic fields are illustrated using contour maps of the field on the planet's surface and discussed in the context of planetary interiors and dynamo generation.

Connerney, J. E. P.↗

NASA NTRS2016

The Habitable Exoplanet (HabEx) imaging mission concept: preliminary science drivers and technical requirements

HabEx is one of 4 possible NASA flagship mission concepts studied for a possible launch in the 2030s. It will be optimized for direct imaging and spectroscopy of habitable exoplanets, and will also enable a wide range of general astrophysics observations. HabEx shall characterize full planetary systems around nearby solar-type stars for the first time, including rocky planets, possible water worlds, gas giants, ice giants, and faint circumstellar debris disks. It will in particular explore our nearest neighbor planetary systems and search for signs of habitability and bio-signatures in the atmospheres of rocky planets. Such high spatial resolution high contrast observations require a large (~3.5 to 8m) stable diffraction- limited optical space telescope, which also opens new unique capabilities for studying the formation and evolution of stars and galaxies. We present here some preliminary science objectives identified for HabEx by our Science and Technology Definition Team (STDT), together with a first look at the key challenges and design trades ahead.

Mennesson, Bertrand↗

NASA NTRS1984

Shock vaporization and the accretion of the icy satellites of Jupiter and Saturn

The role of impact vaporization acting during the formation of the Jovian and Saturnian satellites is examined in an attempt to explain the observed density in terms of composition of these rock and ice objects. A hypothesis is examined which states that the smaller satellites of Saturn having mean densities in the 1.1 to 1.4 Mg/cu m range represent primordial accreted planetesimal condensates formed in the proto-Jovian and Saturnian accretionary planetary discs. These densities are in the range expected for water-ice/silicate mixtures constrained in the solar values of O/Si and O/Mg atomic ratios. It is demonstrated that if the large satellites accreted from the same group of planetesimals which formed the small Saturnian satellites impact vaporization of water upon accretion in a porous regolith, at low H2O partial pressure, can account for the increase in mean planetesimal density from 1.6 Mg/cu m (43% H2O + 57% silicate) to a mean planetary density of 1.9 Mg/cu m for Ganymedean-sized water silicate objects. If impact volatilization of initially porous planetesimals is assumed, it can be demonstrated starting with planetesimals composed of 54% H2O and 40% silicate partial devolatilization upon accretion will yield a Ganymede-sized planet, having a radius of 2600 km and a density of 1.85 kg/cu m, similar to that of Ganymede, Callisto, and Titan.

Ahrens, T. J.↗

NASA NTRS2017

A Vision for Ice Giant Exploration

From Voyager to a Vision for 2050: NASA and ESA have just completed a study of candidate missionsto Uranus and Neptune, the so-called ice giant planets. It is a Pre-Decadal Survey Study, meant to inform the next Planetary Science Decadal Survey about opportunities for missions launching in the 2020's and early 2030's. There have been no space flight missions to the ice giants since the Voyager 2 flybys of Uranus in 1986 and Neptune in 1989. This paper presents some conclusions of that study (hereafter referred to as The Study), and how the results feed into a vision for where planetary science can be in 2050. Reaching that vision will require investments in technology andground-based science in the 2020's, flight during the 2030's along with continued technological development of both ground- and space-based capabilities, and data analysis and additional flights in the 2040's. We first discuss why exploring the ice giants is important. We then summarize the science objectives identified by The Study, and our vision of the science goals for 2050. We then review some of the technologies needed to make this vision a reality.

2050↗

NASA NTRS2022

Radiation-induced D/H Exchange Rate Constants in Aliphatics Embedded in Water Ice

Gas-phase and solid-state chemistry in low-temperature interstellar clouds and cores leads to a D/H enhancement in interstellar ices, which is eventually inherited by comets, meteorites, and even planetary satellites. Hence, the D/H ratio has been widely used as a tracer for the origins of extraterrestrial chemistry. However, the D/H ratio can also be influenced by cosmic rays, which are ubiquitous and can penetrate even dense interstellar molecular cores. The effects of such high-energy radiation on deuterium fractionation have not been studied in a quantitative manner. In this study, we present rate constants for radiation-induced D-to-H exchange for fully deuterated small (1–2 C) hydrocarbons embedded in H2O ice at 20 K and H-to-D exchange for the protiated forms of these molecules in D2O ice at 20 K. We observed larger rate constants for H-to-D exchange in the D2O ice versus D-to-H exchange in H2O ice, which we have attributed to the greater bond strength of C–D versus C–H. We find that the H-to-D exchange rate constants are smaller for protiated methane than ethane, in agreement with bond energies from the literature. We are unable to obtain rate constants for the unsaturated and reactive hydrocarbons ethylene and acetylene. Interpretation of the rate constants suggest that D/H exchange products are formed in abundance alongside radiolysis products. We discuss how our quantitative and qualitative data can be used to interpret the D/H ratios of aliphatic compounds observed throughout space.

Ice destruction↗

NASA NTRS1984

The rotation of the Uranian system

The rotation of Uranus is examined for clues as to the origin of the Solar System. Both theories based on the formation of planets through the accretion of small planetesimals, and theories based on the formation of giant gaseous protoplanets through a gravitational instability in the primitive solar nebula allow for qualitative explanations of the large tilt of Uranus's equator to the orbital plane, and the fact that its satellites lie in the equatorial plane. Models of the planetary interior show that the mass ratio of ice-forming materials to rock in Uranus's interior must be more than about three if the rotation period is about 16 h. Such a large ratio seems to exclude those accretional theories that require most of the nebular gas to be heated to relatively high temperatures before being accreted into the planet.

Podolak, M.↗

NASA NTRS1987

High pressure cosmochemistry of major planetary interiors: Laboratory studies of the water-rich region of the system ammonia-water

Several studies relative to high pressure cosmochemistry of major planetary interiors are summarized. The behavior of gas-ice mixtures at very high pressures, studies of the phase diagram of (NH3) sub x (H2O) sub 1-x at pressures to 5GPa and temperatures from 240 to 370 K, single crystal growth of ammonia dihydrate at room temperature in order to determine their structures by x-ray diffraction, spectroscopy of chemical reactions during shock compression in order to evaluate how the reactions affect the interpretation of equation of state data obtained by shock methods, and temperature and x-ray diffraction measurements made on resistively heated wire in diamond anvil cells in order to obtain phase and structural data relevant to the interiors of terrestrial planets are among the studies discussed.

Nicol, Malcolm↗

NASA NTRS2005

A Tower-based Prototype VHF/UHF Radar for Subsurface Sensing: System Description and Data Inversion Results

Knowledge of subsurface characteristics such as permittivity variations and layering structure could provide a breakthrough in many terrestrial and planetary science disciplines. For Earth science, knowledge of subsurface and subcanopy soil moisture layers can enable the estimation of vertical flow in the soil column linking surface hydrologic processes with that in the subsurface. For planetary science, determining the existence of subsurface water and ice is regarded as one of the most critical information needs for the study of the origins of the solar system. The subsurface in general can be described as several near-parallel layers with rough interfaces. Each homogenous rough layer can be defined by its average thickness, permittivity, and rms interface roughness assuming a known surface spectral distribution. As the number and depth of layers increase, the number of measurements needed to invert for the layer unknowns also increases, and deeper penetration capability would be required. To nondestructively calculate the characteristics of the rough layers, a multifrequency polarimetric radar backscattering approach can be used. One such system is that we have developed for data prototyping of the Microwave Observatory of Subcanopy and Subsurface (MOSS) mission concept. A tower-mounted radar makes backscattering measurements at VHF, UHF, and L-band frequencies. The radar is a pulsed CW system, which uses the same wideband antenna to transmit and receive the signals at all three frequencies. To focus the beam at various incidence angles within the beamwidth of the antenna, the tower is moved vertically and measurements made at each position. The signals are coherently summed to achieve focusing and image formation in the subsurface. This requires an estimate of wave velocity profiles. To solve the inverse scattering problem for subsurface velocity profile simultaneously with radar focusing, we use an iterative technique based on a forward numerical solution of the layered rough surface problem. The layers are each defined in terms of a small number of unknown distributions as given above. An a priori estimate of the solution is first assumed, based on which the forward problem is solved for the backscattered measurements. This is compared with the measured data and using iterative techniques an update to the solution for the unknowns is calculated. The process continues until convergence is achieved. Numerical results will be shown using actual radar data acquired with the MOSS tower radar system in Arizona in Fall 2003, and compared with in-situ measurements.

Moghaddam, Mahta↗

NASA NTRS2008

Global Geologic Map of Europa

Europa, with its indications of a sub-ice ocean, is of keen interest to astrobiology and planetary geology. Knowledge of the global distribution and timing of Europan geologic units is a key step for the synthesis of data from the Galileo mission, and for the planning of future missions to the satellite. The first geologic map of Europa was produced at a hemisphere scale with low resolution Voyager data. Following the acquisition of higher resolution data by the Galileo mission, researchers have identified surface units and determined sequences of events in relatively small areas of Europa through geologic mapping using images at various resolutions acquired by Galileo's Solid State Imaging camera. These works provided a local to subregional perspective and employed different criteria for the determination and naming of units. Unified guidelines for the identification, mapping and naming of Europan geologic units were put forth by and employed in regional-to-hemispheric scale mapping which is now being expanded into a global geologic map. A global photomosaic of Galileo and Voyager data was used as a basemap for mapping in ArcGIS, following suggested methodology of all-stratigraphy for planetary mapping. The following units have been defined in global mapping and are listed in stratigraphic order from oldest to youngest: ridged plains material, Argadnel Regio unit, dark plains material, lineaments, disrupted plains material, lenticulated plains material and Chaos material.

Doggett, T.↗

NASA NTRS2018

The Stratospheric Warming of 2018 in Context of the Earth System

The major stratospheric sudden warming in February 2018 occurred in unison with changes throughout the troposphere in the northern hemisphere. Changes in large-scale dynamics and regional weather patterns are described in this study, along with features in major features of the Earth system, such as sea ice. The focus is on analyses using the Goddard Earth Observing System (GEOS) analyses, weather prediction, and seasonal forecasts. Specific topics to discuss include: - The morphology of the sudden warming, including planetary waves in the troposphere and stratosphere.- Relationships with weather over North America. - Warming over the Arctic and anomalous sea-ice distributions. - Predictability on the one-to-four week timescales. The predictions will be based on routine products generated using the GEOS systems, as well as targeted experiments that focus on the roles of different mechanisms (such as ice-atmosphere interactions).

planetary waves↗

NASA NTRS2016

Tholins as Coloring Agents on Pluto and Other Icy Solar System Bodies

Tholins are refractory organic solids of complex structure and high molecular weight, with a wide range of color ranging from yellow and orange to dark red, and through tan to black. They are made in the laboratory by energy deposition (photons or charged particles) in gases and ices containing the simple molecules (e.g., N2, CH4, CO) found in planetary atmospheres or condensed on planetary surfaces. They are widely implicated in providing the colors and albedos, particularly in the region 0.3-1.0 microns, of several outer Solar System bodies, including Pluto, as well as aerosols in planetary atmospheres such as Titan. Recent color images of Pluto with the New Horizons spacecraft show concentrations of coloring agent(s) in some regions of the surface, and apparent near-absence in other regions. Tholins that may to some degree represent surface chemistry on Pluto have been synthesized in the laboratory by energetic processing of mixtures of the ices (N2, CH4, CO) known on Pluto's surface, or the same molecules in the gas phase. Details of the composition and yield vary with experimental conditions. Chemical analysis of Pluto ice tholins shows evidence of amides, carboxylic acids, urea, carbodiimides, and nitriles. Aromatic/olefinic, amide, and other functional groups are identified in XANES analysis. The ice tholins produced by e- irradiation have a higher concentration of N than UV ice tholins, with N/C approx. 0.9 (versus approx. 0.5 for UV tholins) and O/C approx.0.2. Raman spectra of the electron tholin show a high degree of structural disorder, while strong UV fluorescence indicates a large aromatic content. EUV photolysis of a Pluto gaseous atmosphere analog yields pale yellow solids relatively transparent in the visual, and with aliphatic CH bonds prominent in IR spectra. This or similar material may be responsible for Pluto's hazes.

Tholins↗