MARCI and MOC observations of the atmosphere and surface cap in the north polar region of Mars

We used MGS-MOC and MRO-MARCI daily mapping images of the North Polar Region of Mars from 16 August 2005 (L_s = 270°) to 21 May 2009 (L_s = 270°), covering portions of three consecutive martian years (MY 27-MY 29), to observe the seasonal behavior of the polar ice cap and atmospheric phenomena. The rate of cap regression was similar in MY 28 and MY 29, but was advanced by 3.5° of L_s (∼7-8 sols) in MY 29. The spatial and temporal behaviors of dust and condensate clouds were similar in the two years and generally in accord with prior years. Dust storms (>100 km²) were observed in all seasons, with peak activity occurring at L_s = 10-20° from 50°N to 70°N and at L_s = 135-140° from 70°N to 90°N. The most active quadrant was 0-90°W in MY 28, shifting to 180-270°W in MY 29. The majority of regional storms in both years developed in longitudes from 10°W to 60°W. During late summer the larger storms obscure the North Polar Region in a cloud of dust that transitions to north polar hood condensate clouds around autumnal equinox.Changes in the distribution of perennial ice deposits, especially in Olympia Planum, were observed between the 2 years, with the MY 29 ice distribution being the most extensive observed to date. Modeling suggests that the small, bright ice patches on the residual cap are not the result of slope or elevation effects. Rather we suggest that they are the result of local meteorological effects on ice deposition. The annual darkening and brightening of peripheral areas of the residual cap around summer solstice can be explained by the sublimation of a brighter frost layer revealing an underlying darker, ice rich layer that itself either sublimes to reveal brighter material below or acts as a cold trap, attracting condensation of water vapor that brightens the surface. An alternative explanation invokes transport and deposition of dust on the surface from the cap interior, and later removal of that dust. The decrease in cap albedo and accompanying increase in near surface atmospheric stability may be related to the annual minimum of polar storm activity near northern summer solstice.     

The astronomical theory of climatic change on Mars

We examine the response of Martian climate to changes in solar energy deposition caused by variations of the Martian orbit and obliquity. We systematically investigate the seasonal cycles of carbon dioxide, water, and dust to provide a complete picture of the climate for various orbital configurations. We find that at low obliquity (15°) the atmospheric pressure will fall below 1 mbar; dust storms will cease; thick permanent CO₂ caps will form; the regolith will release CO₂; and H₂O polar ice sheets will develop as the permafrost boundaries move poleward. At high obliquity (35°) the annual average polar temperature will increase by about 10°K, slightly desorbing the polar regolith and causing the atmospheric pressure to increase by not more than 10 to 20 mbar. Summer polar ground temperatures as high as 273°K will occur. Water ice caps will be unstable and may disappear as the equilibrium permafrost boundary moves equatorward. However, at high eccentricity, polar ice sheets will be favored at one pole over the other. At high obliquity dust storms may occur during summers in both hemispheres, independent of the eccentricity cycle. Eccentricity and longitude of perihelion are most significant at modest obliquity (25°). At high eccentricity and when the longitude of perihelion is close to the location of solstice hemispherical asymmetry in dust-storm generation and in polar ice extent and albedo will occur.The systematic examination of the relation of climate and planetary orbit provides a new theory for the formation of the polar laminae. The terraced structure of the polar laminae originates when eccentricity and/or obliquity variations begin to drive water ice off the dusty permanent H₂O polar caps. Then a thin (meters) layer of consolidated dust forms on top of a dirty, slightly thicker (tens of meters) ice sheet and the composite is preserved as a layer of laminae composed predominately of water ice. Because of insolation variation on slopes, a series of poleward- and equatorward-facing scarps are formed where the edges of the laminae are exposed. Independently of orbital variations, these scarps propagate poleward both by erosion of the equatorward slopes and by deposition on the poleward slopes. Scarp propagation resurfaces and recycles the laminae forming the distinctive spiral bands of terraces observed and provides a supply of water to form new permanent ice caps. The polar laminae boundary marks the furthest eqautorward extension of the permanent H₂O caps as the orbit varies. The polar debris boundary marks the furthest equatorward extension of the annual CO₂ caps as the orbit varies.The Martian regolith is now a significant geochemical sink for carbon dioxide. CO₂ has been irreversibly removed from the atmosphere by carbonate formation. CO₂ has also benn removed by regolith adsorption. Polar temperature increases caused by orbital variations are not great enough     

Amazonian northern mid-latitude glaciation on Mars: A proposed climate scenario

Recent geological observations in the northern mid-latitudes of Mars show evidence for past glacial activity during the late Amazonian, similar to the integrated glacial landsystems in the Dry Valleys of Antarctica. The large accumulation of ice (many hundreds of meters) required to create the observed glacial deposits points to significant atmospheric precipitation, snow and ice accumulation, and glacial flow. In order to understand the climate scenario required for these conditions, we used the LMD (Laboratoire de Météorologie Dynamique) Mars GCM (General Circulation Model), which is able to reproduce the present-day water cycle, and to predict past deposition of ice consistent with geological observations in many cases. Prior to this analysis, however, significant mid-latitude glaciation had not been simulated by the model, run under a range of parameters.In this analysis, we studied the response of the GCM to a wider range of orbital configurations and water ice reservoirs, and show that during periods of moderate obliquity (? = 25-35°) and high dust opacity (τ_dust = 1.5-2.5), broad-scale glaciation in the northern mid-latitudes occurs if water ice deposited on the flanks of the Tharsis volcanoes at higher obliquity is available for sublimation. We find that high dust contents of the atmosphere increase its water vapor holding capacity, thereby moving the saturation region to the northern mid-latitudes. Precipitation events are then controlled by topographic forcing of stationary planetary waves and transient weather systems, producing surface ice distribution and amounts that are consistent with the geological record. Ice accumulation rates of ∼10 mm yr⁻¹ lead to the formation of a 500-1000 m thick regional ice sheet that will produce glacial flow patterns consistent with the geological observations.     

A 1 Gyr climate model for Mars: new orbital statistics and the importance of seasonally resolved polar processes

New results from a 1 Gyr integration of the martian orbit are presented along with a seasonally resolved energy balance climate model employed to illuminate the gross characteristics of the long-term atmospheric pressure evolution. We present a new analysis of the statistical variation of the martian obliquity and precession prior to and subsequent to the formation of the Tharsis uplift, and explore the long term effects on the martian climate. We find that seasonal polar cycles have a critical influence on the ability for the regolith to release CO₂ at high obliquities, and find that the atmospheric CO₂ actually decreases at high obliquities due to the cooling effect of polar deposits at latitudes where seasonal caps form. At low obliquity, the formation of massive, permanent polar caps depends critically on the values of the frost albedo, A_frost, and frost emissivity, ?_frost. Using our model with values of A_frost=0.67 and ?_frost=0.55, matched to the NASA Ames General Circulation Model (GCM) results (Haberle et al., 1993, J. Geophys. Res. 98, 3093-3123, and Haberle et al., 2003, Icarus 161, 66-89), we find that permanent caps only form at low obliquities (<13°), suggesting that any permanent deposits on the surface of Mars today may be residuals left over from a period of very low obliquity, or are the result of mechanisms not represented by this model. Thus, contrary to expectations, the martian atmospheric pressure is remarkable static over time, and decreases both at high and low obliquity. Also, from our one billion year orbital model, we present new results on the fraction of time Mars is expected to experience periods of low obliquity and high obliquity.     

The effect of orbital element variations on the mean seasonal daily insolation on Mars

In this paper we briefly study changes in the mean seasonal insolations on the planet Mars caused by significant large-scale variations in the following orbital elements: the eccentricity (e), the obliquity (ε) and the longitude of perihelion (λ _p ). Three orbital configurations have been investigated. In the first, the eccentricity equals successively 0, 0.075, and 0.15, whereas for the obliquity and the longitude of perihelion we took the present values which amount, respectively to 25° and 250°. In the second situation, ε=15, 25, and 35° for a circular orbit (e=0) and with λ _p =250°. In the last model we have sete=0.075 and ε=25° for λ _p =?90,0, and 90°. Although long-term periodic oscillations ofe (first case) and λ _p (third case) produce, respectively, very small or no variations in the average yearly insolation, fluctuations of the above mentioned planetary data strongly effect the mean summer and winter daily insolations. Indeed, the calculations reveal that between the two extreme values of the orbital elements used, the seasonal insolations exhibit a change in amplitude of about 15 to 20% difference over the entire latitude interval. Considering more particularly the second case it is found that the summertime insolation experiences a nearly similar variation as the mean annual daily insolation — i.e., a decrease of about 7% at the equator and a more than twofold increase at the poles. The corresponding mean winter daily insolation varies maximally by approximately 60% in the 60–80° latitude range.     

Periods of active permafrost layer formation during the geological history of Mars: Implications for circum-polar and mid-latitude surface processes

Permafrost is ground remaining frozen (temperatures are below the freezing point of water) for more than two consecutive years. An active layer in permafrost regions is defined as a near-surface layer that undergoes freeze-thaw cycles due to day-average surface and soil temperatures oscillating about the freezing point of water. A “dry” active layer may occur in parched soils without free water or ice but significant geomorphic change through cryoturbation is not produced in these environments. A wet active layer is currently absent on Mars. We use recent calculations on the astronomical forcing of climate change to assess the conditions under which an extensive active layer could form on Mars during past climate history. Our examination of insolation patterns and surface topography predicts that an active layer should form on Mars in the geological past at high latitudes as well as on pole-facing slopes at mid-latitudes during repetitive periods of high obliquity. We examine global high-resolution MOLA topography and geological features on Mars and find that a distinctive latitudinal zonality of the occurrence of steep slopes and an asymmetry of steep slopes at mid-latitudes can be attributed to the effect of active layer processes. We conclude that the formation of an active layer during periods of enhanced obliquity throughout the most recent period of the history of Mars (the Amazonian) has led to significant degradation of impact craters, rapidly decreasing the steep slopes characterizing pristine landforms. Our analysis suggests that an active layer has not been present on Mars in the last ∼5 Ma, and that conditions favoring the formation of an active layer were reached in only about 20% of the obliquity excursions between 5 and 10 Ma ago. Conditions favoring an active layer are not predicted to be common in the next 10 Ma. The much higher obliquity excursions predicted for the earlier Amazonian appear to be responsible for the significant reduction in magnitude of crater interior slopes observed at higher latitudes on Mars. The observed slope asymmetry at mid-latitudes suggests direct insolation control, and hence low atmospheric pressure, during the high obliquity periods throughout the Amazonian. We formulate predictions on the nature and distribution of candidate active layer features that could be revealed by higher resolution imaging data.     

Observations of CO in the atmosphere of Mars with PFS onboard Mars Express

We have analyzed spectra of CO recorded with the instrument PFS onboard Mars Express in the (1-0) band. The dataset we used ranges in time from January until June 2004 (L_S=331^°.17 until L_S=51^°.61; end of Mars Year 26, beginning of Mars Year 27). The aim of this work was to determine the amplitude of the CO mixing ratio departures from the mean globally averaged value currently admitted (8±3×10^-4) [Kaplan, L.D., Connes, J., Connes, P., 1969. Carbon monoxide in the martian atmosphere. Astron. J. 157, L187-L192] as a function of season, local time and location on the planet. We therefore processed the data from 90 calibrated orbits. The globally averaged CO mixing ratio value we derive from our dataset, 11.1×10^-4, is compatible with the range found by Kaplan et al. [1969. Carbon monoxide in the martian atmosphere. Astron. J. 157, L187-L192], although somewhat higher than the “standard” value. However, the CO mixing ratio we retrieve exhibits large variations (roughly between 3×10^-4 and 18×10^-4). Such relative variations have been used on a statistical basis to derive main trends as a function of latitude for three L_S ranges: 331-360^°, 0-30^° and 30-52^°. For the first L_S range, we seem to have an enhancement of the CO mixing ratio towards the northern latitudes, probably linked to the CO₂ condensation in winter on the north polar cap. The situation for the two other L_S ranges is not so clear, mainly as we lack data on the southern hemisphere. We roughly agree with the work of Krasnopolsky [2007. Long-term spectroscopic observations of Mars using IRTF/CSHELL: mapping of O2 dayglow, CO and search for CH4. Icarus 190, 93-102] for L_S=331-360^°, thus confirming the effect of seasonal condensation of CO₂ on the north polar cap, but we have no agreement for other seasons.     

Hydrogen peroxide on Mars: evidence for spatial and seasonal variations

Hydrogen peroxide (H₂O₂) has been suggested as a possible oxidizer of the martian surface. Photochemical models predict a mean column density in the range of 10¹⁵-10¹⁶ cm⁻². However, a stringent upper limit of the H₂O₂ abundance on Mars (9×10¹⁴ cm⁻²) was derived in February 2001 from ground-based infrared spectroscopy, at a time corresponding to a maximum water vapor abundance in the northern summer (30 pr. μm, Ls=112°). Here we report the detection of H₂O₂ on Mars in June 2003, and its mapping over the martian disk using the same technique, during the southern spring (Ls=206°) when the global water vapor abundance was ∼10 pr. μm. The spatial distribution of H₂O₂ shows a maximum in the morning around the sub-solar latitude. The mean H₂O₂ column density (6×10¹⁵ cm⁻²) is significantly greater than our previous upper limit, pointing to seasonal variations. Our new result is globally consistent with the predictions of photochemical models, and also with submillimeter ground-based measurements obtained in September 2003 (Ls=254°), averaged over the martian disk (Clancy et al., 2004, Icarus 168, 116-121).     

Monitoring the perennial martian northern polar cap with MGS MOC

We have used the Mars Global Surveyor Mars Orbiter Camera Wide Angle (MGS MOC WA) dataset to study albedo trends on the martian northern residual cap. Six study regions were selected, the Chasma Boreale source region, three regions near the center of the cap (“fish hook” region, latitude = 87°; “bottle opener” region, latitude = 87°, “steep-shallow” region, latitude = 85°), and two lower latitude regions (crater, latitude = 77°, and polar outlier, latitude = 82°), and the albedos of these six regions were examined. These regions were chosen due to their good temporal coverage in the MOC dataset, as well as having been studied by other researchers (Bass et al., 2000, Icarus 144, 382-396; Calvin and Titus, 2004, Lunar Planet. Sci. XXXV, Abstract 1455). The picture which emerges is complex. Most areas experience a combination of darkening and brightening through the northern summer; only one area consistently brightens (the polar outlier region). A good deal of interannual repeatability in each region's albedo behavior is seen, however. Possible causes for the observed complex behaviors include dust deposition from late summer storms, sintering of frost grains over the course of the summer, and cold trapping of volatiles on bright, cold surfaces.     

Comparison of PFS and TES observations of temperature and water vapor in the martian atmosphere

The interval from L_s = 330° in Mars Year (MY) 26 until L_s = 84° in MY 27 has been used to compare and validate measurements from the Mars Global Surveyor Thermal Emission Spectrometer (TES) and the Mars Express Planetary Fourier Spectrometer (PFS). We studied differences between atmospheric temperatures observed by the two instruments. The best agreement between atmospheric temperatures was found at 50 Pa between 40°S and 40°N latitude, where differences were within ±5 K. For other atmospheric levels, differences as large as ∼25 K were observed between the two instruments at some locations. The largest temperature differences occurred mainly over the Hellas Planitia, Argyre Planitia, Tharsis and Valles Marineris regions.On this basis we report on the variability of the martian atmosphere during the 5.5 martian years of Mars climatology obtained by combining the two data sets from TES and PFS. Atmospheric temperatures at 50 Pa responded to the global-scale dust storms of MY 25 and in MY 28 raising temperatures from ∼220 K to ∼250 K during the daytime. An atmospheric temperature of ∼140 K at 50 Pa was observed poleward of 70°N during northern winter and poleward of 60°S during southern winter each year in both the PFS and TES results. Water vapor observed by the two spectrometers showed consistent seasonal and latitudinal variations.     

North polar frontal clouds and dust storms on Mars during spring and summer

The complete archive of Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) Mars Daily Global Maps (MDGM) are used to study north polar clouds and dust storms that exhibit frontal structures during the spring and summer (L_s 0-180°). Results show that frontal events generally follow the edge of the polar cap during spring and mid/late summer with a gap in the distribution in early summer. The exact duration and timing of the gap vary from year to year. Ten to twenty percent of spring and summer time frontal events exhibit complex morphologies. Distinct temperature signatures are associated with features observed in images in many but not all cases. The general travel paths of the frontal events are eastward around the polar cap. Westward paths exist only at the edge of the polar cap in late spring/early summer. Occasionally, the paths curve toward or away from the polar cap in certain longitude sectors.     

Methane in Martian atmosphere: Average spatial, diurnal, and seasonal behaviour

A large number of spectra measured by the planetary Fourier spectrometer aboard the European Mars Express mission have been studied to identify the average properties of methane in the Martian atmosphere. Using the line at 3018 cm⁻¹, we have studied the seasonal, diurnal, and spatial variations of methane through the analysis of large averages of spectra (more than 1000 measurements). Methane mixing ratio has been obtained simultaneously with water vapour mixing ratio and water ice content, by best fitting (minimising the χ²) the computed averages with synthetic spectra. These spectra were computed for different values of the three parameters (methane and water vapour mixing ratio, and water ice optical depth).The methane mixing ratio shows a slow decrease from northern spring to southern summer with an average value of 14±5 ppbv (part per billion by volume) and it does not show a particular trend with latitude. The methane mixing ratio seems not to be uniform in longitude in the Martian atmosphere, as already reported by Formisano et al. [2004. Detection of methane in the atmosphere of Mars. Science 306, 1758-1761]. Two maxima are present at −40°E and +70°E longitude. In local time, the methane mixing ratio seems to follow the water vapour diurnal cycle. The most important point for future understanding is, however, that there are special orbits in which methane mixing ratio has a very high value.     

Evaporation of ice in planetary atmospheres: Ice-covered rivers on mars

The evaporation rate of water ice on the surface of a planet with an atmosphere involves an equilibrium between solar heating and radiative and evaporative cooling of the ice layer. The thickness of the ice is governed principally by the solar flux which penetrates the ice layer and then is conducted back to the surface. These calculations differ from those of Lingenfelter et al. [(1968) Science161, 266–269] for putative lunar channels in including the effect of the atmosphere. Evaporation from the surface is governed by two physical phenomena: wind and free convection. In the former case, water vapor diffuses from the surface of the ice through a lamonar boundary layer and then is carried away by eddy diffusion above, provided by the wind. The latter case, in the absence of wind, is similar, except that the eddy diffusion is caused by the lower density of water vapor than the Martian atmosphere. For mean Martian insolations the evaporation rate above the ice is ～ 10^?8 g cm^?2 sec^?1. Thus, even under present Martian conditions a flowing channel of liquid water will be covered with ice which evaporates sufficiently slowly that the water below can flow for hundreds of kilometers even with quite modest discharges. Evaporation rates are calculated for a wide range of frictional velocities, atmospheric pressures, and insolations and it seems clear that at least some subset of observed Martian channels may have formed as ice-choked rivers. Typical equilibrium thicknesses of such ice covers are ～ 10 to 30 m; typical surface temperatures are 210 to 235°K. Ice-covered channels or lakes on Mars today may be of substantial biological interest. Ice is a sufficiently poor conductor of heat that sunlight which penetrates it can cause melting to a depth of several meters or more. Because the obliquity of Mars can vary up to some 35°, the increased polar heating at such times seems able to cause subsurface melting of the ice caps to a depth which corresponds to the observed lamina thickness and may be responsible for the morphology of these polar features.     

Mars' water isotope (D/H) history in the strata of the North Polar Cap: Inferences about the water cycle

A time varying stable isotope model for the D/H history of Mars water cycle is developed with variable atmosphere, space loss rate, ground and ice cap flux rates. It considers coupled ground reservoirs and traces D/H in the air and reservoirs secularly and over obliquity cycles. The various flux rates are prescribed time variables that simulate surface flux, and solar driven space loss rates. Predicted bulk averages for the ice cap, ground ice reservoirs and atmosphere span the observed ranges reported by Mumma et al. [Mumma, M.J., Novak, R.E., DiSanti, M.A., Bonev, B., Dello Russo, N., Magee-Sauer, K., 2003. The Martian Atmosphere. Conference Reports of “Sixth International Conference on Mars Atmosphere,” No. 3186]. When the dominant obliquity cycle variations are scaled so that the model delivers present seasonal variations, the present long term bulk D/H average for the ice cap is ∼+2.7 (equivalent to +1700‰ in δ(D) wrt SMOW). The obliquity driven D/H cycle in the ice cap's layers varies between 3 and 6. The smaller more accessible reservoirs have larger bulk averages with the smallest being able to reach D/H values over 9 within ∼¹⁰⁵ years. Small hypothetical solar activity driven variations in the escape rate to space and in the fractionation constant [Krasnopolsky, V.A., Feldman, P.D., 2001. Science 294, 1914-1917] for the escape process can produce a “solar wiggle” whose D/H amplitude can reach 0.1 (δ(D) amplitude of 100‰). Because of the temporal variability, a single modern measured atmospheric D/H ratio at a particular Ls cannot tell very much about the total water inventory of Mars. A bulk average for the Northern Ice Cap and better still a dated vertical profile of D/H from the ice cap would, however, go a long way towards illuminating the “modern” water history of Mars. The age and stability of the Northern Ice Cap and the D/H history locked in the layering is discussed. An ice cap that is very young and exchanges its mass through the atmosphere often will necessarily have a large D/H.     

Mars high resolution gravity fields from MRO, Mars seasonal gravity, and other dynamical parameters

With 2 years of tracking data collection from the MRO spacecraft, there is noticeable improvement in the high frequency portion of the spherical harmonic Mars gravity field. The new JPL Mars gravity fields, MRO110B and MRO110B2, show resolution near degree 90. Additional years of MGS and Mars Odyssey tracking data result in improvement for the seasonal gravity changes which compares well to global circulation models and Odyssey neutron data and Mars rotation and precession (). Once atmospheric dust is accounted for in the spacecraft solar pressure model, solutions for Mars solar tide are consistent between data sets and show slightly larger values (k₂ = 0.164 ± 0.009, after correction for atmospheric tide) compared to previous results, further constraining core models. An additional 4 years of Mars range data improves the Mars ephemeris, determines 21 asteroid masses and bounds solar mass loss (dGM_Sun/dt < 1.6 × 10⁻¹³ GM_Sun year⁻¹).     

Curvilinear features in the southern hemisphere observed by Mars Global Surveyor Mars Orbiter Camera

We have used the complete set of Mars Global Surveyor (MGS) Mars Daily Global Maps (MDGMs) to study martian weather in the southern hemisphere, focusing on curvilinear features, including frontal events and streaks. “Frontal events” refer to visible events that are morphologically analogous to terrestrial baroclinic storms. MDGMs show that visible frontal events were mainly concentrated in the 210-300°E (60-150°W) sector and the 0-60°E sector around the southern polar cap during L_s = 140-250° and L_s = 340-60°. The non-uniform spatial and temporal distributions of activity were also shown by MGS Thermal Emission Spectrometer transient temperature variations near the surface. “Streaks” refer to long curvilinear features in the polar hood or over the polar cap. They are an indicator of the shape of the polar vortex. Streaks in late winter usually show wavy segments between the 180° meridian and Argyre. Model results suggest that the zonal wave number m = 3 eastward traveling waves are important for their formation.     

Temporary liquid water in upper snow/ice sub-surfaces on Mars?

It is investigated whether conditions for melting can be temporarily created in the upper sub-surface parts of snow/ice-packs on Mars at subzero surface temperatures by means of the solid-state greenhouse effect, as occurs in snow- and ice-covered regions on Earth. The conditions for this possible temporary melting are quantitatively described for bolometric albedo values A = 0.8 and A = 0.2, and with model parameters typical for the thermo-physical conditions at snow/ice sites on the surface of present Mars. It is demonstrated by numerical modelling that there are several sets of parameters which will lead to development of layers of liquid water just below the top surface of snow- and ice-packs on Mars. This at least partial liquefaction occurs repetitively (e.g. diurnally, seasonally), and can in some cases lead to liquid water persisting through the night-time in the summer season. This liquid water can form in sufficient amounts to be relevant for macroscopic physical (rheology, erosion), for chemical, and eventually also for biological processes. The creation of temporary pockets of sub-surface water by this effect requires pre-existing snow or ice cover, and thus is more likely to take place at high latitudes, since the present deposits of snow/ice can mainly be found there. Possible rheologic and related erosion consequences of the appearance of liquid sub-surface water in martian snow/ice-packs are discussed in view of current observations of recent rheologic processes.     

Minimum estimates of the amount and timing of gases released into the martian atmosphere from volcanic eruptions

Volcanism has been a major process during most of the geologic history of Mars. Based on data collected from terrestrial basaltic eruptions, we assume that the volatile content of martian lavas was typically ∼0.5 wt.% water, ∼0.7 wt.% carbon dioxide, ∼0.14 wt.% sulfur dioxide, and contained several other important volatile constituents. From the geologic record of volcanism on Mars we find that during the late Noachian and through the Amazonian volcanic degassing contributed ∼0.8 bar to the martian atmosphere. Because most of the outgassing consisted of greenhouse gases (i.e., CO₂ and SO₂) warmer surface temperatures resulting from volcanic eruptions may have been possible. Our estimates suggest that ∼1.1 × 10²¹ g (∼8 ± 1 m m⁻²) of juvenile water were released by volcanism; slightly more than half the amount contained in the north polar cap and atmosphere. Estimates for released CO₂ (1.6 × 10²¹ g) suggests that a large reservoir of carbon dioxide is adsorbed in the martian regolith or alternatively ∼300 cm cm⁻² of carbonates may have formed, although these materials would not occur readily in the presence of excess SO₂. Up to ∼120 cm cm⁻² (2.2 × 10²⁰ g) of acid rain (H₂SO₄) may have precipitated onto the martian surface as the result of SO₂ degassing. The hydrogen flux resulting from volcanic outgassing may help explain the martian atmospheric D/H ratio. The amount of outgassed nitrogen (∼1.3 mbar) may also be capable of explaining the martian atmospheric ¹⁵N/¹⁴N ratio. Minor gas constituents (HF, HCl, and H₂S) could have formed hydroxyl salts on the surface resulting in the physical weathering of geologic materials. The amount of hydrogen fluoride emitted (1.82 × 10¹⁸ g) could be capable of dissolving a global layer of quartz sand ∼5 mm thick, possibly explaining why this mineral has not been positively identified in spectral observations. The estimates of volcanic outgassing presented here will be useful in understanding how the martian atmosphere evolved over time.     

Residual south polar cap of Mars: Stratigraphy, history, and implications of recent changes

The residual south polar cap (RSPC) of Mars includes a group of different depositional units of CO₂ ice undergoing a variety of erosional processes. Complete summer coverage of the RSPC by ∼6-m/pixel data of the Context Imager (CTX) on Mars Reconnaissance Orbiter (MRO) has allowed mapping and inventory of the units in the RSPC. Unit maps and estimated thicknesses indicate the total volume of the RSPC is currently <380 km³, and represents less than 3% of the total mass of the current Mars atmosphere. Scarp retreat rates in the CO₂ ice derived from comparison of High Resolution Imaging Science Experiment (HiRISE) data with earlier images are comparable to those obtained for periods up to 3 Mars years earlier. These rates, combined with sizes of depressions suggest that the oldest materials were deposited more than 125 Mars years ago. Most current erosion is by backwasting of scarps 1-12 m in height. This backwasting is initiated by a series of scarp-parallel fractures. In the older, thicker unit these fractures form about every Mars year; in thinner, younger materials they form less frequently. Some areas of the older, thicker unit are lost by downwasting rather than by the scarp retreat. A surprising finding from the HiRISE data is the scarcity of visible layering of RSPC materials, a result quite distinct from previous interpretations of layers in lower resolution images. Layers ∼0.1 m thick are exposed on the upper surfaces of some areas, but their timescale of deposition is not known. Late summer albedo changes mapped by the CTX images indicate local recycling of ice, although the amounts may be morphologically insignificant. Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data show that the primary material of all the different forms of the RSPC is CO₂ ice with only small admixtures of water ice and dust.     

Estimation of the escape of photoelectrons from Mars in 2004 liberated by the ionization of carbon dioxide and atomic oxygen

Photoelectron peaks in the atmosphere of Mars caused by the ionization of carbon dioxide and atomic oxygen by solar 30.4 nm photons have been observed by the Electron Spectrometer (ELS), a component of the Mars Express (MEx) Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) experiment. Ionization mostly occurs at the Mars exobase with the majority of the photoionized electron flux trapped in the remanent and induced magnetic field, with a portion of that flux escaping the planet down its tail. Since Mars is overall charge neutral, the number of electrons must be identical to the number of ion charges which escape the planet. An estimate of the fraction of the total number of escaping electrons is obtained for the year 2004, specifically those produced by the ionization of carbon dioxide and atomic oxygen by solar 30.4 nm photons. In achieving this process, an illustrative example pass is used to show how the electron spectrum is adjusted for the potential on the spacecraft; then the region of the electron spectrum which shows photoelectron peaks is integrated over energy, yielding a flux of 5.74 × 10⁶ electrons/(cm² s sr). This technique is then applied to a subset of 22 sample averaged spectra from the 2004 data (5 January 2004 through 25 January 2005), yielding an average result of 4.15 × 10⁶ electrons/(cm² s sr) for the 22 cases. The observation cone of 33.75° is used to integrate over solid angle (assuming the flux is constant), giving 4.39 × 10⁶ electrons/(cm² s). This average value was taken as representative of the full data interval. Frequency of occurrence statistics showing about a 6.2% occurrence rate for the 2004 data is applied to give an average escape flux from Mars of 2.72 × 10⁵ electrons/(cm² s) during 2004. By estimating the outflow area as 1.16 × 10¹⁸ cm² at X = −1.5 R_Mars the electron escape rate of 3.14 × 10²³ electrons/s is obtained. Thus about 9.92 × 10³⁰ electrons or 16.5 Mmole of electrons escaped Mars during 2004 due to the ionization of carbon dioxide and atomic oxygen by the He 30.4 nm line. Due to the caveats of the analysis, these derived escape rates should be considered lower limits on the total electron escape rate from Mars.