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Mars theory gets dusted: Streaks may be sand, not water

22 Novembre 2017

But it turns out, the space agency might have been wrong.

Dark features on Mars previously considered evidence for subsurface flowing of water are interpreted by new research as granular flows, where grains of sand and dust slip downhill to make dark streaks, rather than the ground being darkened by seeping water. That's bad news in the hunt for microbes, unfortunately. They get longer and darker, until they abruptly vanish as winter takes hold.

Scientists refer to the mysterious dark streaks on Mars as recurring slope lineae, or RSL.

These features have evoked fascination and controversy since their 2011 discovery, as possible markers for unexpected liquid water or brine on an otherwise dry planet.

Despite our understanding of how RSL form being limited, they were identified in this instance because they are identical to the slopes of sand dunes where movement is caused by dry granular flows.

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The team found that the streaks only existed at the top of steep slopes and flattened out like a pile of dry sand when the ground evens out. It's possible the same thing is happening on Mars, too.

These findings indicate that it is hard for Earth-like life to exist near the surface of Mars owing to the water-restricted conditions that exist on the planet. But now these RSLs may not be the best place to look for life anymore. It's thought that liquid water exists underground, where it's a bit warmer and easier for water to stay a liquid.

However, the study doesn't rule out the presence of Martian water alltogether, only that there aren't any large quantities of it.

Many thousands of these Martian features, collectively called "recurring slope lineae" or RSL, have been identified in more than 50 rocky-slope areas, from the equator to about halfway to the poles. If atmospheric water vapour is a trigger, then a question is why the RSL appear on some slopes but not others.

Mars theory gets dusted: Streaks may be sand, not water