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At least 253 records · Page 14
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NASA NTRS2003

Yearly Comparisons of the Mars North Polar Cap: 1999, 2001, and 2003 MOC Observations

The seasonal cycle of the martian north polar cap has been studied since the time of William Herschel, who published the first quantitative observations of the seasonal recession of the polar caps in 1784. Ground-based observations made after Herschel were summarized by Slipher in 1962. More recent ground-based observations of the north polar cap have been done by Iwasaki et al. Mariner 9 and Viking also made north polar observations. Cantor et al. used Hubble Space Telescope observations between 1990 and 1997 to determine several north polar recessions and Lambert albedos of the cap. Mars Global Surveyor went into orbit around Mars in September 1997. The wide-angle cameras on the Mars Orbiter Camera (MOC) acquire images of the entire planet every day at a resolution of approx. 7.5 km/pixel in both red (575 nm - 625 nm) and blue (400 nm - 450 nm) bandpasses (WAR and WAB). Some polar cap observations were acquired during the aerobraking (AB) and science phasing (SPO) of MGS before systematic mapping began in March, 1999 at Ls = 110 .

Benson, J. L.↗
NASA NTRS1991

The 1990 MB: The first Mars Trojan

Asteroid 1990 MB was discovered by D. H. Levy and H. E. Holt during the course of the Mars and Earth Crossing Asteroid and Comet Survey. An orbit based on a 9 day arc and the asteroid's location near Mars' L5 (trailing Lagrangean) longitude led E. Boswell to speculate that it might be in 1:1 resonance with Mars, analogous to the Trojan asteroids of Jupiter. Subsequent observations strengthened the possibility, and later calculations confirmed it. Thus 1990 MB is the first known asteroid in 1:1 resonance with a planet other than Jupiter. The existence of 1990 MB (a small body most likely between 2 and 4 km in diameter) provides remarkable confirmation of computer simulations. These self consistent n-body simulations demonstrated this sort of stability for Trojans of all the terrestrial planets over at least a 2 million year time base. The discovery of 1990 MB suggests that others of similar or smaller diameter may be found. Using hypothetical populations of Mars Trojans, their possible sky plane distributions were modeled as a first step in undertaking a systematic observational search of Mars' L4 and L5 libration regions.

Innanen, Kimmo A.↗
NASA NTRS1994

The effect of comet Shoemaker-Levy 9 on Jupiter's synchrotron radiation

Solid material from comet Shoemaker-Levy 9 is expected to modify Jupiter's decimetric radio emission. Electrons passing through dust grains suffer a degradation in their energy, while larger sized material absorbs all electrons impinging on it. If there is enough dust and/or larger sized material in the magnetosphere, the effect on the energetic electrons can be observed via their synchrotron radiation, emitted at microwave frequencies. The planet's radio emission is expected to decrease, and the presence of dust induces a hardening in the radio spectrum. We expect the intensity to decrease immediately after cometary material enters the radiation belts; the radio emission continues to drop for many months as electrons diffuse inwards through a dusty magnetosphere. Radio observations of the planet during and after the cometary impact thus yield information on the amount of cometary material (optical depth of the dust and macroscopic material), impacts between cometary material and Jupiter's ring, and the diffusion process of energetic electrons through the magnetosphere.

De Pater, Imke↗
NASA NTRS1996

Jovian X-ray emissions

The Einstein and Rosat observations of X-ray emissions from Jupiter are summarized. Jupiter's soft X-ray emission is observed to originate from the planet's auroral zones, and specifically, from its equatorial region. The processes responsible for these emissions are not established. The brightness distribution of the Jovian X-rays is characterized by the dependence on central meridian longitude and by north-south and morning-afternoon asymmetries. The X-rays observed during the impact of the comet Shoemaker-Levy 9 are believed to be impact-induced brightenings of the X-ray aurora.

Waite, J. H.↗
NASA NTRS1982

Evidence for a distant ( 8700 R sub J) Jovian magnetotail: Voyager 2 observations

A correlative survey of magnetometer (MAG) and Planetary Radio Astronomy (PRA) 1.2 kHz continuum radiation measurements from Voyager 2 provide evidence for at least eight distant Jovian magnetotail sightings occurring about once a month over the first 2/3 of 1981 at distances of approximately 5,000 to 9,000 R sub J. The occurrences of these events are in good agreement with prior Plasma Wave Science and Plasma Science identifications. Observations of these distant magnetotail, or tail filament, encounters appear most prevalent in both MAC and PRA data sets when the spacecraft was closest to the Jupiter-Sun axis at approximately 6,500 R sub J from the planet; the PRA events are also most intense during those times. A specific tail encounter occurring in mid-February 1981 is analyzed and shown to possess a remarkably symmetric magnetic field signature and to have a bipolar field structure in the central region. The bipolarity is characteristic of most of the eight events.

Lepping, R. P.↗
NASA NTRS2005

[Now, The Time for Probes and In-Situ Science]

A viewgraph explaining the need for probes and in situ measurements to understand data from extra solar planet studies is shown. The topics include: 1) To explore the universe and search for life: Probes in Context; 2) What is a probe?; 3) NASA Ames Research Center-founded 1939; 4) Past & Present: Successful Probes and Fly-by's; 5) Thermal Protection Materials and Arc-Jet Facility; 6) Mars Exploration Rovers-Spirit & Opportunity; 7) Bio/Info/Nanotechnology; 8) Technology for Exploration; 9) Award Winning NASA Research Park; 10) Where we need to go; and 11) The Future: Pico Probes

Hubbard, G. Scott↗
NASA NTRS1972

Flying automated laboratories to the planets.

Review of results obtained by instrumented spacecraft in investigation of the planets, mainly Mars. It appears that Mars is a world of varying topographical structure, some of which must have been created by the same processes that sculptured the moon and by others thus far unique in the solar system. The atmosphere is too thin to shield the surface, and there are no traces of liquid water. The very large recent dust storm is discussed. Mariner 9 has revealed definite indication of probable volcanic activity on Mars in recent geologic times.-

Pickering, W. H.↗
NASA NTRS1972

Atmospheric and surface properties of Mars obtained by infrared spectroscopy on Mariner 9

During the eleven month operational lifetime of Mariner 9, the infrared spectroscopy experiment obtained data over a large portion of Mars. Recently obtained spectra indicate that strong seasonal variations in the water vapor distribution over both polar regions occurred. The wettest atmospheric conditions observed so far contain 20 to 30 precipitable microns of water over the north polar cap during northern spring. A low resolution pressure map is presented which covers that portion of the planet between latitudes -60 deg and +25 deg. A more detailed study of the Coprates canyon indicates that at its lowest point the canyon floor must be at least 5 km below the rim. Applications of tidal theory to temperature fields derived from the spectra indicate diurnal surface pressure fluctuations of as much as 12 percent during the great dust storm of 1971-72. Qualitative arguments based on radiative transfer calculations for model dust clouds composed of spherical quartz particles suggest that particle radii during the storm were of the order of a few microns.

Conrath, B.↗
NASA NTRS1983

Voyager 2 observations of Saturn's northern mid-latitude cloud features - Morphology, motions, and evolution

Voyager 2 images provide a basis for detailed study of the morphology and circulation of Saturn's northern midlatitudes. Both Saturn's large-scale cloud bands and the distribution of its local cloud features have a characteristic zonal organization. The region between 30 N and 45 N contains two oppositely directed jets in close proximity, with many bright, active features in the westward jet, and an unusual ribbonlike wave feature encircling the planet in the eastward jet. Several of the smaller features within the westward jet do not remain at fixed latitudes and interact with each other. One group of v-shaped features is found to have periods of high activity correlated with the passage of a cyclonic bright spot. The ribbon wave was Fourier analyzed to determine its spectral composition. The greatest power is near wave number 9, with significant additional peaks appearing at planetary wave numbers 19, 25-27, 35-38, and 47-51. The phase velocity increases with wave number but is not well described by a Rossby-Haurwitz dispersion relation. The curvature of the mean wind profile obtained from cloud tracking indicates that the westward jet exceeds the standard barotropic instability condition, while the eastward jet marginally exceeds the deep-circulation instability condition of Ingersoll and Pollard (1982). The rms eddy velocities on Saturn are less than half as large as those observed on Jupiter.

Sromovsky, L. A.↗
NASA NTRS1992

Variations of the Milankovitch frequencies in time

The sensitivity of the amplitudes and frequencies in the development of the Earth's orbital and rotational elements involved in the astronomical theory of paleoclimates (eccentricity, obliquity, and climate precession), to the Earth-Moon distance and consequently to the length of the day and to the dynamical ellipticity of the Earth has been discussed for the last billions of years. The shortening of the Earth-Moon distance and of the length of the day, as well as the lengthening of the dynamical ellipticity of the Earth back in time induce a shortening of the fundamental astronomical periods for precession and obliquity. At the same time, the amplitudes of the different terms in the development of the obliquity are undergoing a relative enlargement of about 50 percent at 2 x 10(exp 9) yr BP but the independent term is increasing very weakly (less than 0.1 percent). In other words, the value of the obliquity, which lies within a range of 21.7 to 24.9 deg over the Quarternary was restricted to a range of 22.5 to 24.1 deg at 2 x 10(exp 9) yr BP. On the other hand, the amplitudes in the development of the climatic precession do not change. Moreover, these changes in the frequencies and amplitudes for both obliquity and climatic precession are larger for longer period terms. Finally, the periods in the eccentricity development are not influenced by the variation of the lunar distance. But the motion of the solar system, especially of the inner planets, was shown to be chaotic. It means that it is impossible to compute the exact motion of the planets over more than about 100 Myr, and the fundamental frequencies of the systems are not fixed quantities, but are slowly varying with time. As long as we consider the most important terms, the maximum deviation from the present-day value of the 19-kyr precessional period due to the chaotic motion of the solar system only does not reach more than a few tens of years around 80 Myr BP. Therefore the shortening of the obliquity and climatic precession periods is mostly driven by the change in the lunar distance and the consequent variations in the dynamical ellipticity of the Earth's angular speed. At first sight, the deviation in the period for the eccentricity can be neglected, as the chaotic behavior of the solar system implies a relative change of the main periods by less than 0.2 percent, 1.4 percent, and 1.9 percent respectively, this maximum change being achieved around 80 Myr BP. This implies, in particular, that the eccentricity periods for Quarternary climate studies may be considered more or less constant for pre-Quaternay times and equal to their Quaternary values.

Loutre, Marie-France↗
NASA NTRS2016

Trajectories for Europa Flyby Sample Return

Ballistic trajectories are computed which would enable a sample return mission to Europa without capturing, descending, or landing. The low-cost mission concept utilizes a free return trajectory that also involves a close flyby of Europa. Near Europa, a small impactor would kinetically impact the icy moon and generate a plume, subsequently sampled by the spacecraft. A broad search algorithm is developed to construct feasible itineraries, which considers Venus and Earth gravity assist sequences. High-quality solutions are then differentially corrected to be continuous using high-fidelity dynamics. The complete methodology is applicable to other outer-planet moons, notably Enceladus. The outbound VEEGA option is found to signifcantly reduce launch C3 compared to alternate options. The characteristics and quality of the solutions exhibit substantial variation over the 12-year period of Jupiter. Nevertheless, a variety of optimized results are computed with C3 as low as 16.0 sq.km/sq.sec, re-entry speed well below that of the Stardust capsule, and flight times of 9 to 15 years.

Jones, Drew Ryan↗
NASA NTRS1993

Spectral analysis of the gravity and topography of Mars

New spherical harmonic models of the gravity and topography of Mars place important constraints on the structure and dynamics of the interior. The gravity and topography models are significantly phase coherent for harmonic degrees n less than 30 (wavelengths greater than 700 km). Loss of coherence below that wavelength is presumably due to inadequacies of the models, rather than a change in behavior of the planet. The gravity/topography admittance reveals two very different spectral domains: for n greater than 4, a simple Airy compensation model, with mean depth of 100 km, faithfully represents the observed pattern; for degrees 2 and 3, the effective compensation depths are 1400 and 550 km, respectively, strongly arguing for dynamic compensation at those wavelengths. The gravity model has been derived from a reanalysis of the tracking data for Mariner 9 and the Viking Orbiters, The topography model was derived by harmonic analysis of the USGS digital elevation model of Mars. Before comparing gravity and topography for internal structure inferences, we must ensure that both are consistently referenced to a hydrostatic datum. For the gravity, this involves removal of hydrostatic components of the even degree zonal coefficients. For the topography, it involves adding the degree 4 equipotential reference surface, to get spherically referenced values, and then subtracting the full degree 50 equipotential. Variance spectra and phase coherence of orthometric heights and gravity anomalies are addressed.

Bills, Bruce G.↗
NASA NTRS2000

Under the Weather: Space Weather. The Magnetic Field of the Heliosphere

Normally, only people in the far north can enjoy the dancing beauty of the aurora borealis; however, an intense collision of charged solar particles with the Earth's magnetic field can magnify the Northern Lights so much that they are visible in the southern United States. Behind the light show lies enough flux of energetic particles carried by solar wind to render our planet uninhabitable. The Earth's magnetic field, also known as the magnetosphere, is the only thing that shields us from the Sun. Even the magnetosphere cannot fully guard us from the wrath of the Sun. In March 1989, a powerful solar flare hit Earth with such energy that it burned out transformers in Quebec's electrical grid, plunging Quebec and the eastern United States into darkness for more than 9 hours. Northern lights and energy grid overloads are not the only ways that a solar wind can affect us. A solar storm in July 1999 interrupted radio broadcasts. Solar activity can disorient radars and satellite sensors, break up cell phone connections, and threaten the safety of astronauts. A large bombardment of solar particles can even reduce the amount of ozone in the upper atmosphere. Magnetohydrodynamics (MHD), the study of magnetic fields in magnetized plasmas, can help scientists predict, and therefore prepare for, the harmful side effects of solar weather in the magnetosphere.

Roberts, Aaron↗
NASA NTRS1979

Mars surface composition from reflectance spectroscopy - A summary

Visible and near-infrared reflectance spectra and multispectral maps of the Martian surface are discussed, and implications of the data for the composition of the Martian surface are considered. Spacecraft and earth-based telescopic observations have confirmed the generally bimodal albedo distribution of the planet, dividing the surface into bright and dark regions. Mars spectra are characterized by the presence of strong Fe(+3) absorption, which is attributed to various ferric oxide minerals. Interpretations of the spectra from the dark regions indicate a basaltic or ultramafic source rock. Evidence for water ice or a highly desiccated metal hydrate has been obtained, along with evidence for CO2-ice only in the south polar cap. Mariner 9 observations of Martian dust suggest the presence of rather acidic rock or mineral particles, or a montmorillonite-type clay. Prospects for the future study of Martian surface composition include continuing earth-based spectrophotometric studies, and high-spectral-resolution mapping of a significant portion of the surface by the Galileo spacecraft and the next Mars mission.

Singer, R. B.↗
NASA NTRS2012

The Probing In-Situ With Neutron and Gamma Rays (PING) Instrument for Planetary Composition Measurements

The Probing In situ with Neutrons and Gamma rays (PING) instrument (formerly named PNG-GRAND) [I] experiment is an innovative application of the active neutron-gamma ray technology successfully used in oil field well logging and mineral exploration on Earth over many decades. The objective of our active neutron-gamma ray technology program at NASA Goddard Space Flight Center (NASA/GSFC) is to bring PING to the point where it can be flown on a variety of surface lander or rover missions to the Moon, Mars, Venus, asteroids, comets and the satellites of the outer planets and measure their bulk surface and subsurface elemental composition without the need to drill into the surface. Gamma-Ray Spectrometers (GRS) have been incorporated into numerous orbital planetary science missions. While orbital measurements can map a planet, they have low spatial and elemental sensitivity due to the low surface gamma ray emission rates reSUlting from using cosmic rays as an excitation source, PING overcomes this limitation in situ by incorporating a powerful neutron excitation source that permits significantly higher elemental sensitivity elemental composition measurements. PING combines a 14 MeV deuterium-tritium Pulsed Neutron Generator (PNG) with a gamma ray spectrometer and two neutron detectors to produce a landed instrument that can determine the elemental composition of a planet down to 30 - 50 cm below the planet's surface, The penetrating nature of .5 - 10 MeV gamma rays and 14 MeV neutrons allows such sub-surface composition measurements to be made without the need to drill into or otherwise disturb the planetary surface, thus greatly simplifying the lander design, We are cun'ently testing a PING prototype at a unique outdoor neutron instrumentation test facility at NASA/GSFC that provides two large (1.8 m x 1.8 m x ,9 m) granite and basalt test formations placed outdoors in an empty field, Since an independent trace elemental analysis has been performed on both these Columbia River basalt and Concord Gray granite materials, these large samples present two known standards with which to compare PING's experimentally measured elemental composition results, We will present both gamma ray and neutron experimental results from PING measurements of the granite and basalt test formations in various layering configurations and compare the results to the known composition.

Parsons, A.↗
NASA NTRS1994

Episodic large-scale overturn of two-layer mantles in terrestrial planets

It is usually assumed that the upper and lower mantles of a chemically stratified planet are arranged so that the upper mantle is chemically less dense and that these layers convect separately. Possible buoyant overturn of the two mantle layers has not previously been considered. Such overturn would initially occur when thermal expansion of a chemically denser lower mantle more than offsets the compositional density difference between the layers, reversing the relative sense of buoyancy. Once overturn has occurred, the chemically denser, but thermally less dense upper mantle cools more efficiently than the lower mantle and loses its relative thermal buoyancy. If mixing is slow, this leads to repeated overturns that result in thermal histories that differ radically from those obtained without this large-scale overturning. Thermal evolution calculations, for a two-layer mantle over a wide range of parameter space, show that large-scale overturn occurs cyclically with a well-defined period. This period depends most strongly on the viscosity of the lower mantle, to which it is approximately proportional. Geologically interesting overturn periods on the order of 10(exp 7) to 10(exp 9) years result for lower mantle viscosities of 10(exp 22) to 10(exp 24) Pa s for the Earth and Venus, and 10(exp 21) to 10(exp 23) Pa s for Mars. The mantles of Mercury and the Moon are too thin to permit two-layer convection, and therefore the model is not appropriate for them. Overturn cannot occur on Earth or Venus if the compositional density difference between the layers exceeds about 4%, or on Mars if it exceeds about 2%. Large-scale mantle overturn could have significant tectonic consequences such as the initiation of a new plate tectonic cycle on the Earth or a major resurfacing event on Mars or Venus. Such episodic events in the evolution of a planet are not easily explained by whole mantle thermal convection.

Herrick, David L.↗
NASA NTRS1973

Topographical coordinates from Mariner 9 observations of the Martian surface

Results of Mariner 9 determinations of the coordinates of selected topographical features on Mars. An attempt is made to project uncertainties in such determinations, together with uncertainties in spin-rate and in the inertial orientation of the spin axis of Mars, to some epoch in the distant future, and, to examine the impact of further imaging data from a Mars synchronous orbiter in reducing the uncertainty of the location of any given surface feature on the planet relative to the orbiter. The effect of residual navigational uncertainties, and uncertainties in celestial orientation of the imaging system, on such determinations is discussed.

Mohan, S. N.↗
NASA NTRS1979

Planetary geodesy

The results of investigations of the geodesy of the planets and their satellites conducted during the period 1975 - 1978 are surveyed. Analysis of the photographic data of Mercury taken by Mariner 10 have revealed the mass, oblateness, radius rotation period and density of the panet, and allowed the high-resolution mapping of the surface. Earth-based radar imagery has permitted the identification of large-scale topographic features on Venus. Knowledge of the gravitational field of Mars has been improved by Mariner 9 and Viking tracking data, and the global topography and geometric figure of Mars have been derived. Doppler and ranging tracking data from the Viking landers have provided data for the precise determination of Martian rotational dynamics and the topographic features and figures of Phobos and Deimos have been observed. Pioneer 10 and 11 data have yielded information on the mass, gravitational field and dynamic parameters of Jupiter. Discoveries of a satellite of Pluto and a set of rings around Uranus have been made, the rotation of Uranus and Neptune have been measured, and the geodetic properties of the rings and satellites of Saturn have been investigated. Future developments in planetary geodesy are expected from continued Viking data and the Pioneer Venus probe and Voyager probes to Jupiter and Saturn.

Michael, W. H., Jr.↗