Data from NASA’s Curiosity rover has revealed two sets of ancient wave ripples on Marssignatures of long-dry bodies of water preserved in the rock record.
Wave ripples are small ripples on the sandy shores of lake beds, created when wind-driven water moves from side to side. The two sets of undulations indicate the previous presence of shallow water which was open to Martian air, not covered by ice as some climate models would require.
Ripples are one of the clearest indicators of an ancient body of standing water that the geological record can provide. The team, led by Caltech, estimates that the ripples formed about 3.7 billion years agoindicating that the Martian atmosphere and climate must have been warm and dense enough to support liquid water open to the air at that time.
The research is described in an article that appears in the journal Science Advances. John Grotzinger, Caltech’s Harold Brown Professor of Geology, and Michael Lamb, professor of geology, are the study’s principal investigators.
“The shape of the ripples could only have formed under water exposed to the atmosphere and under the action of the wind“says postdoctoral researcher Claire Mondro, first author of the study, in a statement.
Lamb, an expert on the interactions between sediment, water and atmosphere on Earth, created computer models of the ripples to determine the size of the lake that created them. The ripples are small: only about 6 millimeters high and spaced 4 to 5 centimeters apart. These small ripples in fine sand are formed by small wave actionand this restriction limits the original environment to a shallow lake less than about 2 meters deep.
The period of ripple formation, about 3.7 billion years ago, was a time in Mars’ history when it was assumed that the planet was becoming drier.
“Expanding the period of time that liquid water was present expands the possibilities of microbial habitability later in the history of Mars,” says Mondro.
The ripples were discovered in 2022 by NASA’s Curiosity rover as it traversed the Gale Crater region of Mars. A set of undulations, the Prow outcrop, was discovered in a region that once contained windblown dunes. The other set, found nearby in the rocky Amapari Marker Band, suggests the presence of a lake with up to 2 meters of watera little later in the history of Mars than Prow. The two sets of ripples suggest that the atmospheric conditions for their formation occurred at multiple points in time.
“The discovery of wave ripples is an important advance for Mars paleoclimatic science,” says Grotzinger, former project scientist for the Curiosity mission, Mars Science Laboratory (MSL).
“We have been searching for these features since the Opportunity and Spirit landers They began their missions in 2004. Previous missions, starting with Opportunity in 2004, discovered ripples formed by water flowing across the surface of ancient Mars, but it was not known for certain whether that water ever accumulated to form lakes or shallow seas.
“The Curiosity rover discovered evidence of long-lived ancient lakes in 2014, and now, 10 years later, Curiosity has discovered ancient lakes that did not have icewhich offers an important perspective on the planet’s early climate.”
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