Margarita Marinova

Mega-impact formation of the Mars hemispheric dichotomy

The Mars hemispheric dichotomy is expressed as a dramatic difference in elevation, crustal thickness and crater density between the southern highlands and northern lowlands (which cover ∼42% of the surface). Despite the prominence of the dichotomy, its origin has remained enigmatic and models for its formation largely untested. Endogenic degree-1 convection models with north–south asymmetry are incomplete in that they are restricted to simulating only mantle dynamics and they neglect crustal evolution, whereas exogenic multiple impact events are statistically unlikely to concentrate in one hemisphere. A single mega-impact of the requisite size has not previously been modelled. However, it has been hypothesized that such an event could obliterate the evidence of its occurrence by completely covering the surface with melt or catastrophically disrupting the planet. Here we present a set of single-impact initial conditions by which a large impactor can produce features consistent with the observed dichotomy’s crustal structure and persistence. Using three-dimensional hydrodynamic simulations, large variations are predicted in post-impact states depending on impact energy, velocity and, importantly, impact angle, with trends more pronounced or unseen in commonly studied smaller impacts. For impact energies of ∼(3–6) × 1029 J, at low impact velocities (6–10 km s-1) and oblique impact angles (30–60°), the resulting crustal removal boundary is similar in size and ellipticity to the observed characteristics of the lowlands basin. Under these conditions, the melt distribution is largely contained within the area of impact and thus does not erase the evidence of the impact’s occurrence. The antiquity of the dichotomy is consistent with the contemporaneous presence of impactors of diameter 1,600–2,700 km in Mars-crossing orbits, and the impact angle is consistent with the expected distribution.

The Icebreaker Life Mission to Mars: a search for biomolecular evidence for life.

The search for evidence of life on Mars is the primary motivation for the exploration of that planet. The results from previous missions, and the Phoenix mission in particular, indicate that the ice-cemented ground in the north polar plains is likely to be the most recently habitable place that is currently known on Mars. The near-surface ice likely provided adequate water activity during periods of high obliquity, ≈ 5 Myr ago. Carbon dioxide and nitrogen are present in the atmosphere, and nitrates may be present in the soil. Perchlorate in the soil together with iron in basaltic rock provides a possible energy source for life. Furthermore, the presence of organics must once again be considered, as the results of the Viking GCMS are now suspect given the discovery of the thermally reactive perchlorate. Ground ice may provide a way to preserve organic molecules for extended periods of time, especially organic biomarkers. The Mars Icebreaker Life mission focuses on the following science goals: (1) Search for specific biomolecules that would be conclusive evidence of life. (2) Perform a general search for organic molecules in the ground ice. (3) Determine the processes of ground ice formation and the role of liquid water. (4) Understand the mechanical properties of the martian polar ice-cemented soil. (5) Assess the recent habitability of the environment with respect to required elements to support life, energy sources, and possible toxic elements. (6) Compare the elemental composition of the northern plains with midlatitude sites. The Icebreaker Life payload has been designed around the Phoenix spacecraft and is targeted to a site near the Phoenix landing site. However, the Icebreaker payload could be supported on other Mars landing systems. Preliminary studies of the SpaceX Dragon lander show that it could support the Icebreaker payload for a landing either at the Phoenix site or at midlatitudes. Duplicate samples could be cached as a target for possible return by a Mars Sample Return mission. If the samples were shown to contain organic biomarkers, interest in returning them to Earth would be high.

Nearing the cold-arid limits of microbial life in permafrost of an upper dry valley, Antarctica

Some of the coldest and driest permafrost soils on Earth are located in the high-elevation McMurdo Dry Valleys (MDVs) of Antarctica, but little is known about the permafrost microbial communities other than that microorganisms are present in these valleys. Here, we describe the microbiology and habitable conditions of highly unique dry and ice-cemented permafrost in University Valley, one of the coldest and driest regions in the MDVs (1700 m above sea level; mean temperature −23 °C; no degree days above freezing), where the ice in permafrost originates from vapour deposition rather than liquid water. We found that culturable and total microbial biomass in University Valley was extremely low, and microbial activity under ambient conditions was undetectable. Our results contrast with reports from the lower-elevation Dry Valleys and Arctic permafrost soils where active microbial populations are found, suggesting that the combination of severe cold, aridity, oligotrophy of University Valley permafrost soils severely limit microbial activity and survival.

The physics, biology, and environmental ethics of making mars habitable.

The considerable evidence that Mars once had a wetter, more clement, environment motivates the search for past or present life on that planet. This evidence also suggests the possibility of restoring habitable conditions on Mars. While the total amounts of the key molecules--carbon dioxide, water, and nitrogen--needed for creating a biosphere on Mars are unknown, estimates suggest that there may be enough in the subsurface. Super greenhouse gases, in particular, perfluorocarbons, are currently the most effective and practical way to warm Mars and thicken its atmosphere so that liquid water is stable on the surface. This process could take approximately 100 years. If enough carbon dioxide is frozen in the South Polar Cap and absorbed in the regolith, the resulting thick and warm carbon dioxide atmosphere could support many types of microorganisms, plants, and invertebrates. If a planet-wide martian biosphere converted carbon dioxide into oxygen with an average efficiency equal to that for Earths biosphere, it would take > 100,000 years to create Earth-like oxygen levels. Ethical issues associated with bringing life to Mars center on the possibility of indigenous martian life and the relative value of a planet with or without a global biosphere.

Distribution of depth to ice-cemented soils in the high-elevation Quartermain Mountains, McMurdo Dry Valleys, Antarctica

Abstract We report on 475 measurements of depth to ice-cemented ground in four high-elevation valleys of the Quartermain Mountains, McMurdo Dry Valleys, Antarctica. These valleys have pervasive ice-cemented ground, and the depth to ice-cemented ground and the ice composition may be indicators of climate change. In University Valley, the measured depth to ice-cemented ground ranges from 0–98 cm. There is an overall trend of increasing depth to ice-cemented ground with distance from a small glacier at the head of the valley, with a slope of 32 cm depth per kilometre along the valley floor. For Farnell Valley, the depth to ice-cemented ground is roughly constant (c. 30 cm) in the upper and central parts of the valley, but increases sharply as the valley descends into Beacon Valley. The two valleys north of University Valley also have extensive ice-cemented ground, with depths of 20–40 cm, but exhibit no clear patterns of ice depth with location. For all valleys there is a tendency for the variability in depth to ice-cemented ground at a site to increase with increasing depth to ice. Snow recurrence, solar insolation, and surface albedo may all be factors that cause site to site variations in these valleys.

Radiative‐convective model of warming Mars with artificial greenhouse gases

[1] Artificial greenhouse gases could be used to warm Mars in order to make it habitable. Here we present new laboratory measurements of the thermal infrared absorption spectra of seven artificial greenhouse gases (CF 4 , C 2 F 6 , C 3 F 8 , SF 6 , CF 3 Cl, CF 3 Br, CF 2 Cl 2 ) at concentrations from 10 -7 up to unity. We used a radiative-convective multilayer model to compute the warming caused by a mixture of the four fluorine-based greenhouse gases. The results show that for current Mars, C 3 F 8 produces the largest warming: 0.56 K and 33.5 K for partial pressures of 10 -3 Pa and 1 Pa, respectively. Averaged over partial pressures from 0.01 to 1 Pa, the range of most interest for planetary ecosynthesis, CF 4 , C 2 F 6 , and SF 6 were 17%, 49%, and 48% as effective as C 3 F 8 , respectively. The optimal mixture of the four fluorine-based greenhouse gases, taking into account the overlapping of their absorption bands, was 16% more effective than pure C 3 F 8 , averaged over the range 0.01 Pa to 1 Pa. Energy balance calculations suggest that the addition of ∼0.2 Pa of the best greenhouse gases mixture or ∼0.4 Pa of C 3 F 8 would shift the equilibrium to the extent that CO 2 would no longer be stable at the Martian poles and a runaway greenhouse effect would result.

Testing of a 1 meter Mars IceBreaker Drill in a 3.5 meter Vacuum Chamber and in an Antarctic Mars Analog Site

In this paper we report on the development of a rotary-percussive sampling drill: the IceBreaker. The purpose of the drill is to penetrate at least 1 meter in icy-regolith and in ice, and acquire sub-surface sample for science analysis. The drill was tested at a Mars analog site in the Dry Valleys of Antarctica and inside a 3.5 meter vacuum chamber in icy-soil, ice and ice with 2% perchlorate. In all cases, the drill reached ~1 meter depth in approximately one hour. The average power was 100 Watts and Weight on Bit was less than 100 Newton. This corresponds to the drilling energy of 100 Whr. In each case approximately 500 cubic centimeters of sample was recovered and deposited into sterile bags.

Formation and evolution of buried snowpack deposits in Pearse Valley, Antarctica, and implications for Mars

Abstract Buried snowpack deposits are found within the McMurdo Dry Valleys of Antarctica, which offers the opportunity to study these layered structures of sand and ice within a polar desert environment. Four discrete buried snowpacks are studied within Pearse Valley, Antarctica, through in situ observations, sample analyses, O-H isotope measurements and numerical modelling of snowpack stability and evolution. The buried snowpack deposits evolve throughout the year and undergo deposition, melt, refreeze, and sublimation. We demonstrate how the deposition and subsequent burial of snow can preserve the snowpacks in the Dry Valleys. The modelled lifetimes of the buried snowpacks are dependent upon subsurface stratigraphy but are typically less than one year if the lag thickness is less than c. 7 cm and snow thickness is less than c. 10 cm, indicating that some of the Antarctic buried snowpacks form annually. Buried snowpacks in the Antarctic polar desert may serve as analogues for similar deposits on Mars and may be applicable to observations of the north polar erg, buried ice at the Mars Phoenix landing site, and observations of buried ice throughout the martian Arctic. Numerical modelling suggests that seasonal snows and subsequent burial are not required to preserve the snow and ice on Mars.

LunarVader: Testing of a 1 meter lunar drill in a 3.5 meter vacuum chamber and in the Antarctic lunar analog site

In this paper we report on the development of a rotary-percussive sampling drill, LunarVader. The purpose of the drill is to penetrate at least 1 meter in icy-regolith and acquire sub-surface sample for science analysis and for the In Situ Resource Utilization (ISRU). The drill was tested in a lunar analog site of the Ross Island, in the Antarctic and inside the 3.5 meter vacuum chamber in ice-bound JSC-1a lunar soil simulant. In both cases, the drill reached ~1 meter depth in approximately one hour. The average power was 100 Watts and Weight on Bit was less than 100 Newton. This corresponds to the drilling energy of 100 Whr. In each case approximately 500 grams of sample was recovered and autonomously deposited into a sterile bag.