The Murray Buttes. Click to see August 11, 2016 post.
The uncertainty of science: Though Curiosity has found apparent evidence of past liquid water during its early travels on the floor of Gale Crater, scientists have now concluded that the first small mesas and buttes it traveled past back in 2016, dubbed the Murray Buttes, were not formed by the flow of liquid water but by wind reshaping ancient sand dunes. From the press release:
The lower part of Mount Sharp is composed of ancient lakebed sediments. These sediments accumulated on the lakebed when the crater flooded, shortly after its formation 3.8 billion years ago. Curiosity has spent much of the last nine years investigating these rocks for signs of habitability.
Dr Banham added: “More than 3.5 billion years ago this lake dried out, and the lake bottom sediments were exhumed and eroded to form the mountain at the centre of the crater – the present-day Mount Sharp. The flanks of the mountain are where we have found evidence that an ancient dune field formed after the lake, indicating an extremely arid climate.”
This conclusion comes from a paper released March 30th in the Journal of Geophysical Research: Planets, and uses data obtained by Curiosity from August to September, 2016 (see rover updates from August 11, 2016, from August 28, 2016, and from September 13, 2016).
At that time Curiosity was still on the floor of Gale Crater, where that lake is thought to have once existed, but had reached the first tiny foothills and dune fields that sit at the base of Mt. Sharp.
The scientists also note that this data means that the floor of Gale Crater has not been amicable to life for at least 3 billion years. Dune fields are not places where life prospers, and the Murray Buttes required a lot of time for the original dunes to solidify into the multiple thin layers that exist today.
Click to see August 28, 2016 post.
The photo above illustrates the many thin layers in these buttes. Each layer, only inches thick at most, represents the past existence of a dune anywhere from 13 to 130 feet high that was slowly swept through by Mars’ very thin atmosphere, depositing a new layer behind it. To get that many layers, all squeezed to become soft rock, required a lot of time and many many millions of seasons, during which the environment would have been very hostile to life.
These conclusions also suggest that we really do not yet know what the environment was like in Gale Crater when this theorized past lake existed. This data even suggests that this past liquid water could have been underground, not on the surface, a water table that was liquid because it was not exposed to Mars’ cold and very thin atmosphere.
We do not know, however, since the data available remains very preliminary.