* Astronomy

Craters and channels in Hephaestus Fossae

5 June 2009
The High Resolution Stereo Camera on ESA's Mars Express orbiter has obtained images of Hephaestus Fossae, a region on Mars dotted with craters and channel systems.
Hephaestus Fossae lies at about 21° North and 126° East on the Red Planet. Named after the Greek god of fire, it extends for more than 600 km on the western flank of Elysium Mons in the Utopia Planitia region.
Obtained on 28 December 2007, the images have a ground resolution of about 16 m/pixel. They show that the region has channel systems of unknown origin. 

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Fresh Secondary Crater of Zumba Crater in Daedalia Planum (PSP_004874_1505)
Credit: NASA/JPL/University of Arizona

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This image taken at a high sun angle shows the relatively unshadowed pristine and youthful rayed crater Zumba.
The crater's rim-to-rim diameter is approximately 3 kilometres with a depth of about 620 metres, and its rim rises about 200 metres above the surrounding lava-filled plains of Daedalia Planum, just southwest of the great Tharsis volcanoes. (For an appreciation of the dimensions of this crater, see the anaglyph for Zumba.) Zumba is approximately 25% deeper than the average Martian crater of this size - just one of several attributes that suggests it is a very fresh crater.
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The International Astronomical Union (IAU) has approved the name Asimov for the 84-kilometre wide Martian crater located at 47.0S, 355.0W.
The crater is named after Isaac Asimov (1920-1992).

Title: Astrobiological Implications of Early Mars Environment
Authors: Helmut Lammer

The history of the Martian atmosphere can be divided into Noachian, Hesperian, and Amazonian evolutionary periods. During the Noachian period, Mars and its surrounding atmosphere were altered by collisions with asteroids and comets, and the young Suns elevated X-ray and extreme ultraviolet (EUV) radiation and solar wind. After the Sun arrived at the Zero-Age-Main-Sequence (ZAMS), heavy noble gases, like nonradiogenic Xe isotopes, may have been hydrodynamically fractionated during the accretion phase of the planet to their present composition, with corresponding depletions and fractionations of lighter primordial atmospheric species such as deuterium (D) or H atoms.
Subsequently, the CO2 surface-pressure history and the isotopic evolution of atmospheric species during this early period were determined by the interplay between impact erosion and impact delivery, carbonate precipitation and oxidation, outgassing and carbonate recycling, and perhaps by feedback stabilization under greenhouse conditions (Carr, 1987; Pepin, 1994; Manning et al., 2006). This period was also influenced by thermal and nonthermal atmospheric loss processes (e.g., Donahue, 2004; Kulikov et al., 2007; Lammer et al., 2008), which would depend partly on the time of the on-set of the martian magnetic dynamo, the field strength and decrease time of the magnetic moment, and the radiation and particle environment of the young Sun.
The second period in the evolution of the martian atmosphere can be characterised by a uniform atmospheric loss, which was enhanced due to the vanished intrinsic magnetic field and various nonthermal atmospheric escape processes that resulted in the present surface pressure of about 710 mbar.

Helmut Lammer. Astrobiology. January/February 2009, 9(1): 42-44. doi:10.1089/ast.2009.0923.