Searching for Developments Outside of Earth
By admin September 14, 2016

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Four years into its travels across Mars, NASA’s Curiosity rover faces an unexpected challenge: winding its way safely among dozens of dark streaks that could indicate water seeping from the red planet’s hill sides.

Although scientists would love to investigate the streaks at close range, strict international rules prohibit Curiosity from touching any part of Mars that could host liquid water, to prevent contamination. But as the rover begins climbing the mountain Aeolis Mons next month, it will probably pass within a few kilometers of a dark streak that grew and shifted between February and July 2012, in ways suggestive of flowing water.

The streaks – dubbed recurring slope lineae (RSLs), because they appear, fade and re­-appear seasonally on steep slopes – were first reported[1] on Mars five years ago in a handful of places. The total count is now up to 452 possible RSLs. More than half of those are in the enormous equatorial canyon of Valles Marineris, but they also appear at other latitudes and longitudes.

Dark Marks

RSLs typically measure a few meters across and hundreds of meters long. One leading idea is that they form when the chilly Martian surface warms just enough to thaw an ice dam in the soil, allowing water to begin seeping downhill. When temperatures drop, the water freezes and the hillside lightens again until next season. But the picture is complicated by factors such as potential salt in the water; brines may seep at lower temperatures than fresher water[1]. Other possible explanations for the streaks include water condensing from the atmosphere, or the flow of bone-dry debris. So far, the rover has taken pictures of eight of the 58 locations and seen no changes. The features are lines on slopes, but they have not yet recurred.

But the rover’s sheer unexpected proximity to potential RSLs has NASA re-evaluating its planetary-protection protocols. Curiosity was only partly sterilized before going to Mars, and experts at JPL and NASA headquarters in Washington DC are calculating how long the remaining microbes could survive in Mars’s harsh atmosphere — as well as what weather conditions could transport them several kilometers away and possibly contaminate a water seep.

The work is an early test for the NASA Mars rover slated to launch in 2020, which will look for life and collect and stash samples for possible return to Earth. RSLs exist at several of the rover’s eight possible landing sites.

For now, Curiosity is finishing exploring the Murray formation. This area is made of sediments from the bottom of ancient lakes — the sort of potentially life-supporting environment the rover was sent to find. Curiosity’s second extended mission begins on October 1st.

Barring disaster, the rover’s lifespan will be set by its nuclear-power source, which will continue to dwindle in coming years through radioactive decay. Curiosity still has kilometers to scale on Aeolis Mons as it moves towards its final destination, a sulfate-rich group of rocks.

End Note:

[1] McEwen, A. S. et al. Science 333, 740–743 (2011).

[2] Ojha, L. et al. Nature Geosci. 8, 829–832 (2015).

For more information:

Why hunting for life in Martian water will be a tricky task

Water seems to flow freely on Mars

Mystery of slick Martian slopes gets less slippery

Dark streaks guide search for life on Mars

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