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NASA NTRS1978

The occultation of Epsilon Gem by Mars as observed from Agassiz Station

Observations of the April 8, 1976, occultation of Epsilon Gem by Mars made at the Agassiz Station of the Harvard College Observatory have been analyzed to yield temperature profiles of the Martian atmosphere for number densities between 10 to the 13th and 10 to the 15th power per cu cm. Pronounced wavelike structure is evident in both immersion and emersion profiles, with a peak-to-peak variation of up to 50 K and a vertical scale of 20 km.

Liller, W.↗

NASA NTRS1990

Sensitivity studies of Mars orbiters for Mars gravity recovery

The purpose of the study is to assess the Mars orbiters with regard to their sensitivity to the Mars gravity field. The sensitivity is evaluated and quantified in terms of the magnitude and frequency of the orbiter position and velocity perturbations. The strengths and weaknesses of each orbiter, including Mariner 9, Viking 1 and 2, Mars Observer, Phobos, and Deimos, when used as a sensor of the Mars gravity field are assessed. It is shown that Mariner 9 and Viking data supply strong information on the low degree and order coefficients, with Mariner 9 contributing to the even-ordered terms out to about degrees 10 to 12. Phobos and Deimos are shown to be able to contribute to the lowest degrees of the gravity field, while the Mars Observer, in addition to the lower-degree and -order harmonics, will be responsive to coefficients as high as degree and order 50. Emphasis is placed on the spacecraft orbit plane orientation allowing the radial velocity perturbations to be measured by the Doppler data, thus enhancing the sensitivity to the gravitational signal.

Rosborough, George W.↗

NASA NTRS1993

Spatial variation in the seasonal south polar cap of Mars as observed by Mariner 7

Spatial variations in infrared spectra of the seasonal south polar cap of Mars were noted by the original Mariner 7 IRS instrument team as well as in subsequent examinations of the Mariner 7 data set. Up to now, however, there has been little effort to synthesize this information to understand variations in the south seasonal cap as a function of position or latitude. An attempt to quantify the spectra is made by providing estimates of CO2 grain sizes as well as upper limits on the amount of water frost contained in the polar collar. The variation in brightness at two wavelengths as well as the band depth of a weak CO2-ice feature at 2.28 microns as a function of spectrum number or subsequent location on the cap is presented. The full spectra, corrected only for the solar incidence angle, of three of the most significant areas are compared.

Calvin, Wendy M.↗

NASA NTRS1991

Measurements of dust on Mars to be obtained from upcoming missions

Measurements of dust on the Mars surface and in its atmosphere will be made from several upcoming missions. The best defined missions are Mars Observer, the Soviet Mars 94 mission, and the Mars Environment Survey (MESUR) mission. A discussion is presented of what measurements pertaining to airborne or surface dust will be made and what properties can be inferred from them. The payloads for the latter two missions are not yet determined. In all cases, only that information which pertains to dust is included; each mission contains additional instruments that provide no information on this topic. Following the discussion of individual instruments is a summary of the types of measurements and observations that will be made from the ensemble collection of instruments and missions, and a brief discussion of the types of measurements of dust which will not be made.

Jakosky, Bruce M.↗

NASA NTRS1991

Observations of Mars, Uranus, Neptune, Io, Europa, Ganymede, and Callisto at a wavelength of 2.66 mm

An accurate thermal model of Mars is presently used as a calibrator for 2.66-mm brightness temperature observations of Uranus, Neptune, and the Galilean satellites. While the measurements for Io, Europa, and Callisto, are consistent with thermal models of the lunar type, Ganymede is found to be anomalous. It appears that the near surface of Ganymede differs from that of the other satellites in some unknown fashion, perhaps by scattering more strongly at short wavelengths.

Muhleman, Duane O.↗

NASA NTRS1992

Mid-infrared spectra of Martian komantiite

Synthetic mid-infrared emissive spectra of basalts of possible Martian komatiitic compositions were generated to show what might be seen in data returned from the Thermal Emission Spectrometer (TES). TES is flying on the Mars Observer arriving at Mars in late 1993. The synthetic Martian komatiite spectra were generated using mineralogy based on Shergottite, Nakhlite, and Chassigny (SNC) meteorites and Viking X-Ray Fluorescence (XRF) data. These data sets provide strong evidence for the existence of ultramafic lavas on Mars, particularly lavas of komatiitic composition.

Reyes, David P.↗

NASA NTRS1987

Goldstone radar observations of Mars: The 1986 opposition

Radar echoes from the planet Mars were obtained on 27 S-band (wavelength = 12.5 cm) and 2 X-band (wavelength = 3.5 cm) tracks using the Goldstone Solar System Radar. These observations took advantage of the favorable 1986 opposition since the Earth-Mars distance was 0.40 AU at opposition and radar echo strength is proportional to inverse-fourth-power of the distance to the target. The coverages of the Goldstone observations are summarized. The observations were conducted via the CW-spectra techniques described by Harmon et al. A continuous tone was transmitted at Mars and the radar echo was sampled to obtain a Doppler spread spectrum. Each received event was separated into polarized (opposite sense circular) and depolarized (same sense circular) periods. There was one successful ranging run which had a resolution of 2 microseconds. This should yield surface heights accurate to 300 meters.

Thompson, T. W.↗

NASA NTRS2002

Mars Radar Observations with the Goldstone Solar System Radar

The Goldstone Solar System Radar (GSSR) has successfully collected radar echo data from Mars over the past 30 years. As such, the GSSR has played a role as a specific mission element within Mars exploration. The older data provided local elevation information for Mars, along with radar scattering information with global resolution. Since the upgrade to the 70-m Deep Space Network (DSN) antenna at Goldstone completed in 1986, Mars data has been collected during all but the 1997 Mars opposition. Radar data, and non-imaging delay-Doppler data in particular, requires significant data processing to extract elevation, reflectivity and roughness of the reflecting surface. The spatial resolution of these experiments is typically some 20 km in longitude by some 150 km in latitude. The interpretation of these parameters while limited by the complexities of electromagnetic scattering, do provide information directly relevant to geophysical and geomorphic analyses of Mars. The usefulness of radar data for Mars exploration has been demonstrated in the past. Radar data were critical in assessing the Viking Lander 1 site as well as, more recently, the Pathfinder landing site. In general, radar data have not been available to the Mars exploration community at large. A project funded initially by the Mars Exploration Directorate Science Office at the Jet Propulsion Laboratory (JPL), and later funded by NASA's Mars Data Analysis Program has reprocessed to a common format a decade's worth of raw GSSR Mars delay-Doppler data in aid of landing site characterization for the Mars Program. These data will soon be submitted to the Planetary Data System (PDS). The radar data used were obtained between 1988 and 1995 by the GSSR, and comprise some 63 delay-Doppler radar tracks. Of these, 15 have yet to be recovered from old 9-track tapes, and some of the data may be permanently lost.

Haldemann, A. F. C.↗

NASA NTRS1972

Mars - Are observed white clouds composed of H2O.

A total of 252 occurrences of white clouds are studied. Water abundances are compared with those of white clouds as a function of latitude on Mars. It appears not necessarily to be the case that observed cloud frequencies will always follow water abundances. Martian white cloud frequencies tend to follow the distribution of water both seasonally and latitudinally on the planet, which strongly suggests that most white clouds are formed from water vapor.

Wells, R. A.↗

NASA NTRS1998

An Overview of Observations of Mars' North Polar Region From the Mars Global Surveyor Laser Altimeter

Since its arrival at Mars on September l5, 1997, the Mars Global Surveyor (MGS) has been in a near-polar elliptical orbit, with the orbital eccentricity decreasing during orbital periapse passes where the spacecraft aerobrakes through the martian atmosphere. The Mars Orbiter Laser Altimeter (MOLA), an instrument on the MGS, has the ability to range to the martian surface during nonaerobraking passes. MOLA can operate whenever the range from the spacecraft to the surface is less than 786 km, with the limit determined by the number of bits encoded for the range measurement During the capture orbit, aerobraking hiatus, and science phasing orbit (SPO) mission phases, MOLA acquired approximately 200 profiles across the northern hemisphere of Mars and provided more than 2,000,000 measurements of the radius of the planet. These observations cover the region from the north pole to about 10 degrees S latitude with a precision of a few tens of centimeters and an accuracy (at present) of about 30 in. Absolute accuracy of the elevations is limited by the knowledge of the MGS orbits; these should improve later in the mission due to a more optimal tracking geometry, an improved gravitational field, and the use of the high-gain antenna once the spacecraft achieves its approximately 400-km-altitude circular mapping orbit. MOLA measurements so far show a planet with a low, flat high-latitude region in the north and a higher, topographically rougher terrain nearer the equator. The north polar cap stands approximately 2-3 km above the surrounding terrain and displays deep chasms and complex structure. MOLA measurements of elevation, 1064-nm reflectivity, and backscattered pulse width indicate that the layered terrains are composed mainly of ice.

Smith, D. E.↗

NASA NTRS2004

Solar particle events observed at Mars: dosimetry measurements and model calculations

During the period from March 13, 2002 to mid-September, 2002, six solar particle events (SPE) were observed by the MARIE instrument onboard the Odyssey Spacecraft in Martian Orbit. These events were observed also by the GOES 8 satellite in Earth orbit, and thus represent the first time that the same SPE have been observed at these separate locations. The characteristics of these SPE are examined, given that the active regions of the solar disc from which the event originated can usually be identified. The dose rates at Martian orbit are calculated, both for the galactic and solar components of the ionizing particle radiation environment. The dose rates due to galactic cosmic rays (GCR) agree well with the HZETRN model calculations. Published by Elsevier Ltd on behalf of COSPAR.

Non-NASA Center↗

NASA NTRS1995

The circum-Chryse region as a possible example of a hydrologic cycle on Mars: Geologic observations and theoretical evaluation

Moore, Jeffrey M.↗

NASA NTRS1995

The circum-Chryse region as a possible example of a hydrologic cycle on Mars: Geologic observations and theoretical evaluation

The transection and superposition relationships among channels, chaos, surface materials units, and other features in the circum-Chryse region of Mars were used to evaluate relative age relationships and evolution of flood events. Channels and chaos in contact (with one another) were treated as single discrete flood-carved systems. Some outflow channel systems form networks and are inferred to have been created by multiple flood events. Within some outflow channel networks, several separate individual channel systems can be traced to a specific chaos which acted as flood-source area to that specific flood channel. Individual flood-carved systems were related to widespread materials units or other surface features that served as stratigraphic horizons. Chryse outflow channels are inferred to have formed over most of the perceivable history of Mars. Outflow channels are inferred to become younger with increasing proximity to the Chryse basin. In addition, outflow channels closer to the basin show a greater diversity in age. The relationship of subsequent outflow channel sources to the sources of earlier floods is inferred to disfavor episodic flooding due to the progressive tapping of a juvenile near-surface water supply. Instead, we propose the circum-Chryse region as a candidate site of past hydrological recycling. The discharge rates necessary to carve the circum-Chryse outflow channels would have inevitably formed temporary standing bodies of H2O on the Martian surface where the flood-waters stagnated and pooled (the Chryse basin is topographically enclosed). These observations and inferences have led us to formulate and evaluate two hypotheses: (1) large amounts of the sublimated H2O off the Chryse basin flood lakes precipitated (snowed) onto the flood-source highlands and this H2O was incorporated into the near surface, recharging the H2O sources, making possible subsequent deluges; and (2) ponded flood-water in Chryse basin drained back down an anti basinward dipping subsurface layer accessed along the southern edge of the lake, recharging the flood-source aquifers. H2O not redeposited in the flood-source region was largely lost to the hydrologic cycle. This loss progressively lowered the vitality of the cycle, probably by now killing it. Our numerical evaluations indicate that of the two hypotheses we formulated, the groundwater seep cycle seems by far the more viable. Optimally, approx. 3/4 of the original mass of an ice-covered cylindrical lake (albedo 0.5, 1 km deep, 100-km radius, draining along its rim for one quarter of its circumference into substrata with a permeability of 3000 darcies) can be modeled to have moved underground (on timescales of the order of 10(exp 3) years) before the competing mechanisms of sublimation and freeze down choked off further water removal. Once underground, this water can travel distances equal to the separation between Chryse basin and flood-source sites in geologically short (approx. 10(exp 6) year-scale) times. Conversely, we calculate that optimally only approx. 40% of the H2O carried from Chryse can condense at the highlands, and most of the precipitate would either collect at the base of the highlands/lowlands scarp or sublimate at rates greater than it would accumulate over the flood-source sites. Further observations from forthcoming missions may permit the determination of which mechanisms may have operated to recycle the Chryse flood-waters.

Moore, Jeffrey M.↗

NASA NTRS1995

The Circum-Chryse Region as a Possible Example of a Hydrologic Cycle on Mars: Geologic Observations and Theoretical Evaluation

The transection and superposition relationships among channels, chaos, surface materials units, and other features in the circum-Chryse region of Mars were used to evaluate relative age relationships and evolution of flood events. Channels and chaos in contact (with one another) were treated as single discrete flood-carved systems. Some outflow channel systems form networks and are inferred to have been created by multiple flood events. Within some outflow channel networks, several separate individual channel systems can be traced to a specific chaos which acted as flood-source area to that specific flood channel. Individual flood-carved systems were related to widespread materials units or other surface features that served as stratigraphic horizons. Chryse outflow channels are inferred to have formed over most of the perceivable history of Mars. Outflow channels are inferred to become younger with increasing proximity to the Chryse basin. In addition, outflow channels closer to the basin show a greater diversity in age. The relationship of subsequent outflow channel sources to the sources of earlier floods is inferred to disfavor episodic flooding due to the progressive tapping of a juvenile near-surface water supply. Instead, we propose the circum-Chryse region as a candidate site of past hydrological recycling. The discharge rates necessary to carve the circum-Chryse outflow channels would have inevitably formed temporary standing bodies of H2O on the Martian surface where the flood-waters stagnated and pooled (the Chryse basin is topographically enclosed). These observations and inferences have led us to formulate and evaluate two hypotheses: (1) large amounts of the sublimated H2O off the Chryse basin flood lakes precipitated (snowed) onto the flood-source highlands and this H2O was incorporated into the near surface, recharging the H2O sources, making possible subsequent deluges; and (2) ponded flood-water in Chryse basin drained back down an anti basinward dipping subsurface layer accessed along the southern edge of the lake, recharging the flood-source aquifers. H2O not redeposited in the flood-source region was largely lost to the hydrologic cycle. This loss progressively lowered the vitality of the cycle, probably by now killing it. Our numerical evaluations indicate that of the two hypotheses we formulated, the groundwater seep cycle seems by far the more viable. Optimally, approximately 3/4 of the original mass of an ice-covered cylindrical lake (albedo 0.5, 1 km deep, 100-km radius, draining along its rim for one quarter of its circumference into substrata with a permeability of 3000 darcies) can be modeled to have moved underground (on timescales of the order of 10(exp 3) years) before the competing mechanisms of sublimation and freeze down choked off further water removal. Once underground, this water can travel distances equal to the separation between Chryse basin and flood-source sites in geologically short (approximately 10(exp 6) year-scale) times. Conversely, we calculate that optimally only approximately 40% of the H2O carried from Chryse can condense at the highlands, and most of the precipitate would either collect at the base of the highlands/lowlands scrap or sublimate at rates greater than it would accumulate over the flood-source sites. Further observations from forthcoming missions may permit the determination of which mechanisms may have operated to recycle the Chryse flood-waters.

Moore, Jeffrey M.↗

NASA NTRS2003

OMEGA Observations of Mars Analogue Rocks

In the last 20 years, imaging spectrometry in the visible and near infrared onboard spacecraft has become an essential technique to study surfaces and atmospheres of planetary objects, prior and in addition to in-situ analyses. Remote sensing experiments analyzing the sunlight reflected by planetary surfaces can be used to derive the mineralogical composition and physical properties of the natural surfaces and atmospheres observed. This technique was successfully used on Mars with ISM instrument. As an improvement of ISM, OMEGA onboard MARS-EXPRESS will play a key role in the mineralogical mapping of the Martian surface. We present the reflectance measurements made with OMEGA during on ground calibration sessions on natural slabs of rocks and minerals part of a database which will be used on similar future American instruments (as CRISM onboard MRO). We discuss the implication on the scientific capabilities of OMEGA instrument.

Bonello, G.↗

NASA NTRS2021

Maximizing Dust Devil Follow-up Observations on Mars Using Cubesats and On-board Scheduling

Several million dust devil events occur on Mars every day. These events last, on average, about 30 minutes and range in size from meters to hundreds of meters in diameter. Designing low-cost missions that will improve our knowledge of dust devil formation and evolution, and their connection to atmospheric dynamics and the dust cycle, is fundamental to informing future crewed Mars lander missions about surface conditions. In this paper we present a mission for a constellation of low orbiting Mars cubesats, each carrying imagers with agile pointing capabilities. The goal is to maximize the number of dust devil follow-up observations through real-time, on-board scheduling. We study scenarios where cubesats are equipped with a 2.5 degree boresight angle camera that accommodates five slew positions (including nadir). We assume a concept of operations where the cubesats autonomously survey the surface of Mars and can autonomously detect dust devils from their surface imagery. When a dust devil is detected, the constellation is autonomously re-tasked through an on-board distributed scheduler to capture as many follow-on images of the event as possible, so as to study its evolution. The cubesat orbits are propagated assuming two-body dynamics and the ground tracks and camera field of view are computed assuming a spherical Mars. Realistic inter-agent communication link opportunities are computed and included in our optimization, which allow for real-time event detection information to be shared within the constellation. We compare against a powerful ``omniscient'' mission which has a priori knowledge of all dust devil activity to show the gap between predicted performance and the best possible outcome. In particular, we show that the communications are especially important for acquiring follow-up observations, and that a realistic distributed scheduling mechanism is sufficient to capture nearly all dust devil observations that are possible for a given orbit configuration.

Hook, Joshua Vander↗

NASA NTRS1991

Thermal environment of Mars

Thermal observations of Mars are reviewed focusing on surface and atmospheric temperatures. Data obtained indicate that the effect of increasing dust in the atmosphere is to reduce diurnal temperature variation at the surface, while enhancing atmospheric thermal variation. Atmospheric thermal effects can be induced by global dust storms even in regions of polar night. Maximum temperatures occur near the equator in summer or at local sites with sunward facing slopes, where low surface thermal inertias make it possible to achieve values up to about 310 K. Radiation and convection in the daytime affect atmospheric temperatures near the surface, which are limited by radiation at night. Results of thermal observations confirm that Mars' thermal state and climate can significantly vary from year to year, due to the variation in dust activity.

Martin, T. Z.↗

NASA NTRS1990

Modeling issues in precision orbit determination for Mars orbiter

This paper examines the accuracy of recent Mars gravity models and the importance of perturbations due to the Mars radiation pressure and the Martian moons, Phobos and Deimos, on the trajectories of Mars orbiters. A linear orbit perturbation theory is used to characterize the patterns of gravity field near resonances for the Viking and Mariner 9 spacecraft. These resonances are shown to have considerable power and their potential for contributing to Mars gravity solutions is emphasized. It is shown that some of the same resonance orders which appear in the Viking orbits, dominate the radial orbit error spectrum for Mars Observer. Results of orbit determination simulations at the Goddard Space Flight Center show that the perturbations caused by the Martian moons and the Mars radiation pressure are larger than 0.1 mm/s, the expected precision of the Mars Observer Doppler tracking data. Tests with the Viking Doppler data indicate that best analysis of these data mandates the inclusion of the Phobos gravitational perturbation in the modeling of Viking spacecraft trajectories.

Lemoine, Frank G.↗