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PubMed2002

Optically stimulated luminescence signals of polymineral fine grains in the JSC Mars-1 soil simulant sample.

The results of various experiments which characterise the optically stimulated luminescence (OSL) signals from polymineral fine grains of a Martian soil simulant sample (JSC Mars-1) are presented. The blue-green stimulated luminescence signal has greater thermal stability than the infrared stimulated luminescence signal for pre-heat temperatures between 250 degrees C and 400 degrees C. Fading tests over a 2 month storage period at 20 degrees C indicate that in some aliquots of JSC Mars-1 both the blue-green stimulated luminescence and the infrared stimulated luminescence signals fade by as much as 50%, whereas in others there is no evidence of significant fading. Dose recovery experiments demonstrate that equivalent dose (measured/given) ratio varies from aliquot to aliquot, and the underestimation in dose is less than 5% for at least one aliquot, for both the infrared and blue-green stimulated luminescence signals.

Luminescent Measurements↗

PubMed2000

Radiation exposure for human Mars exploration.

One major obstacle to human space exploration is the possible limitations imposed by the adverse effects of long-term exposure to the space environment. Even before human space flight began, the potentially brief exposure of astronauts to the very intense random solar energetic particle events was of great concern. A new challenge appears in deep-space exploration from exposure to the low-intensity heavy-ion flux of the galactic cosmic rays since the missions are of long duration, and accumulated exposures can be high. Because cancer induction rates increase behind low to moderate thicknesses of aluminum shielding, according to available biological data on mammalian exposures to galactic cosmic ray-like ions, aluminum shield requirements for a Mars mission may be prohibitively expensive in terms of mission launch costs. Alternative materials for vehicle construction are under investigation to provide lightweight habitat structures with enhanced shielding properties. In the present paper, updated estimates for astronaut exposures on a Mars mission are presented and shielding properties of alternative materials are compared with aluminum.

Cosmic Radiation↗

PubMed2006

The carbon cycle on early Earth--and on Mars?

One of the goals of the present Martian exploration is to search for evidence of extinct (or even extant) life. This could be redefined as a search for carbon. The carbon cycle (or, more properly, cycles) on Earth is a complex interaction among three reservoirs: the atmosphere; the hydrosphere; and the lithosphere. Superimposed on this is the biosphere, and its presence influences the fixing and release of carbon in these reservoirs over different time-scales. The overall carbon balance is kept at equilibrium on the surface by a combination of tectonic processes (which bury carbon), volcanism (which releases it) and biology (which mediates it). In contrast to Earth, Mars presently has no active tectonic system; neither does it possess a significant biosphere. However, these observations might not necessarily have held in the past. By looking at how Earth's carbon cycles have changed with time, as both the Earth's tectonic structure and a more sophisticated biology have evolved, and also by constructing a carbon cycle for Mars based on the carbon chemistry of Martian meteorites, we investigate whether or not there is evidence for a Martian biosphere.

Biological Evolution↗

PubMed2002

Maps of subsurface hydrogen from the high energy neutron detector, Mars Odyssey.

After 55 days of mapping by the High Energy Neutron Detector onboard Mars Odyssey, we found deficits of high-energy neutrons in the southern highlands and northern lowlands of Mars. These deficits indicate that hydrogen is concentrated in the subsurface. Modeling suggests that water ice-rich layers that are tens of centimeters in thickness provide one possible fit to the data.

Atmosphere↗

PubMed2003

Fluid core size of Mars from detection of the solar tide.

The solar tidal deformation of Mars, measured by its k2 potential Love number, has been obtained from an analysis of Mars Global Surveyor radio tracking. The observed k2 of 0.153 +/- 0.017 is large enough to rule out a solid iron core and so indicates that at least the outer part of the core is liquid. The inferred core radius is between 1520 and 1840 kilometers and is independent of many interior properties, although partial melt of the mantle is one factor that could reduce core size. Ice-cap mass changes can be deduced from the seasonal variations in air pressure and the odd gravity harmonic J3, given knowledge of cap mass distribution with latitude. The south cap seasonal mass change is about 30 to 40% larger than that of the north cap.

Atmosphere↗

PubMed2004

Evidence for precipitation on Mars from dendritic valleys in the Valles Marineris area.

Dendritic valleys on the plateau and canyons of the Valles Marineris region were identified from Thermal Emission Imaging System (THEMIS) images taken by Mars Odyssey. The geomorphic characteristics of these valleys, especially their high degree of branching, favor formation by atmospheric precipitation. The presence of inner channels and the maturity of the branched networks indicate sustained fluid flows over geologically long periods of time. These fluvial landforms occur within the Late Hesperian units (about 2.9 to 3.4 billion years old), when Mars was thought to have been cold. Our results suggest a period of warmer conditions conducive to hydrological activity.

Climate↗

PubMed2005

Nightglow in the upper atmosphere of Mars and implications for atmospheric transport.

We detected light emissions in the nightside martian atmosphere with the SPICAM (spectroscopy for the investigation of the characteristics of the atmosphere of Mars) ultraviolet (UV) spectrometer on board the Mars Express. The UV spectrum of this nightglow is composed of hydrogen Lyman alpha emission (121.6 nanometers) and the gamma and delta bands of nitric oxide (NO) (190 to 270 nanometers) produced when N and O atoms combine to produce the NO molecule. N and O atoms are produced by extreme UV photodissociation of O2, CO2, and N2 in the dayside upper atmosphere and transported to the night side. The NO emission is brightest in the winter south polar night because of continuous downward transport of air in this region at night during winter and because of freezing at ground level.

Atmosphere↗

PubMed2005

Olivine and pyroxene diversity in the crust of Mars.

Data from the Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) on the Mars Express spacecraft identify the distinct mafic, rock-forming minerals olivine, low-calcium pyroxene (LCP), and high-calcium pyroxene (HCP) on the surface of Mars. Olivine- and HCP-rich regions are found in deposits that span the age range of geologic units. However, LCP-rich regions are found only in the ancient Noachian-aged units, which suggests that melts for these deposits were derived from a mantle depleted in aluminum and calcium. Extended dark regions in the northern plains exhibit no evidence of strong mafic absorptions or absorptions due to hydrated materials.

Absorption↗

PubMed2005

Ancient Mars: wet in many places.

New results from the Mars Express Orbiter mission reveal multiple deposits of minerals formed in the presence of liquid water. They reinforce the conclusion that ancient Mars was warmer and wetter than it is today, and increase the number of promising localities to search for evidence of past life.

Exobiology↗

PubMed2005

A sporadic third layer in the ionosphere of Mars.

The daytime martian ionosphere has been observed as a two-layer structure with electron densities that peak at altitudes between about 110 and 130 kilometers. The Mars Express Orbiter Radio Science Experiment on the European Mars Express spacecraft observed, in 10 out of 120 electron density profiles, a third ionospheric layer at altitude ranges of 65 to 110 kilometers, where electron densities, on average, peaked at 0.8 x 10(10) per cubic meter. Such a layer has been predicted to be permanent and continuous. Its origin has been attributed to ablation of meteors and charge exchange of magnesium and iron. Our observations imply that this layer is present sporadically and locally.

Atmosphere↗

PubMed1997

Warming early Mars with carbon dioxide clouds that scatter infrared radiation.

Geomorphic evidence that Mars was warm enough to support flowing water about 3.8 billion years ago presents a continuing enigma that cannot be explained by conventional greenhouse warming mechanisms. Model calculations show that the surface of early Mars could have been warmed through a scattering variant of the greenhouse effect, resulting from the ability of the carbon dioxide ice clouds to reflect the outgoing thermal radiation back to the surface. This process could also explain how Earth avoided an early irreversible glaciation and could extend the size of the habitable zone on extrasolar planets around stars.

Atmosphere↗

PubMed1998

Mars global surveyor mission: overview and status.

The Mars Global Surveyor (MGS) spacecraft achieved a 45-hour elliptical orbit at Mars on 11 September 1997 after an 11-month cruise from Earth. The mission is acquiring high-quality global observations of the martian surface and atmosphere and of its magnetic and gravitational fields. These observations will continue for one martian year.

Atmosphere↗

PubMed1998

Detection of atomic deuterium in the upper atmosphere of Mars.

High-resolution spectroscopy of Mars' atmosphere with the Hubble Space Telescope revealed the deuterium Lyman alpha line at an intensity of 23 +/- 6 rayleighs. This measured intensity corresponds to HD/H2 = 1.5 +/- 0.6 x 10(-4), which is smaller by a factor of 11 than HDO/H2O. This indicates that fractionation of HD/H2 relative to that of HDO/H2O is not kinetically controlled by the rates of formation and destruction of H2 and HD but is thermodynamically controlled by the isotope exchange HD + H2O left and right arrow HDO + H2. Molecular hydrogen is strongly depleted in deuterium relative to water on Mars because of the very long lifetime of H2 (1200 years). The derived isotope fractionation corresponds to an estimate of a planetwide reservoir of water ice about 5 meters thick that is exchangeable with the atmosphere.

Atmosphere↗

PubMed1998

Implications of Mars Pathfinder data for the accretion history of the terrestrial planets.

Accretion models of the terrestrial planets often assume planetary bulk compositions with nonvolatile element abundance ratios equivalent to those of C1 carbonaceous chondrites. The moment of inertia factor of Mars reported by the Pathfinder team is inconsistent with a bulk planet C1 Fe/Si ratio or Fe content, which suggests that C1 chondrite accretion models are insufficient to explain the formation of Mars and the other terrestrial planets. Future planetary accretion models will have to account for variations in bulk Fe/Si ratios among the terrestrial planets.

Carbon↗

PubMed1999

The global topography of Mars and implications for surface evolution.

Elevations measured by the Mars Orbiter Laser Altimeter have yielded a high-accuracy global map of the topography of Mars. Dominant features include the low northern hemisphere, the Tharsis province, and the Hellas impact basin. The northern hemisphere depression is primarily a long-wavelength effect that has been shaped by an internal mechanism. The topography of Tharsis consists of two broad rises. Material excavated from Hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary. The present topography has three major drainage centers, with the northern lowlands being the largest. The two polar cap volumes yield an upper limit of the present surface water inventory of 3.2 to 4.7 million cubic kilometers.

Evolution, Planetary↗

PubMed2000

A wetter, younger Mars emerging.

Most researchers have believed that the days were long gone when water splashed on the surface of Mars or even near it. Now continuing analyses of martian meteorites and stunning images from the Mars Global Surveyor (MGS), which has been in orbit since 1997, are breathing new life into the Red Planet. Last month's announcement that the camera aboard MGS had spied signs of geologically recent--possibly even ongoing--water seeps has caught everyone's attention. Other, perhaps more persuasive, signs also suggest that water may even now flow on or beneath the frigid surface.

Exobiology↗

PubMed2000

A low temperature transfer of ALH84001 from Mars to Earth.

The ejection of material from Mars is thought to be caused by large impacts that would heat much of the ejecta to high temperatures. Images of the magnetic field of martian meteorite ALH84001 reveal a spatially heterogeneous pattern of magnetization associated with fractures and rock fragments. Heating the meteorite to 40 degrees C reduces the intensity of some magnetic features, indicating that the interior of the rock has not been above this temperature since before its ejection from the surface of Mars. Because this temperature cannot sterilize most bacteria or eukarya, these data support the hypothesis that meteorites could transfer life between planets in the solar system.

Crystallization↗

PubMed1995

Loss of atmosphere from Mars due to solar wind-induced sputtering.

Because Mars does not have a strong intrinsic magnetic field, the atmosphere is eroded by interactions with the solar wind. Early solar-system conditions enhanced the sputtering loss. It is calculated that approximately 3 bars of carbon dioxide (CO2) have been sputtered over the last 3.5 billion years. This significant increase over the previous estimate by Luhmann et al. of approximately 0.14 bar of CO2 is the result of the development of a more complete model. The model also predicts slightly greater loss of water--approximately 80 meters instead of the approximately 50 meters predicted by Luhmann et al. Because estimates of CO2 on early Mars range from 0.5 to 5 bars, the 0.14-bar estimate is insignificant but the approximately 3-bar estimate will have a large effect on our understanding of the planet's evolution.

Atmosphere↗