Ridges in impact craters on Mars appear to be fossils of cracks in the Martian surface,
formed by minerals deposited by flowing water. Water flowing beneath
the surface suggests life may once have been possible on Mars. Networks
of narrow ridges found in impact craters on Mars appear to be the
fossilized remnants of underground cracks through which water once
flowed, according to a new analysis by researchers from Brown University.
The study supports the idea that the subsurface environment on Mars
once had an active hydrology and could be a good place to search for
evidence of past life.
The ridges, many of them hundreds of meters in length and a few meters
wide, had been noted in previous research, but how they had formed was
not known. Saper and colleague, Fred Mustard, thought they might once
have been faults and fractures that formed underground when impact
events rattled the planet’s crust.
Water, if present in the subsurface, would have circulated through
the cracks, slowly filling them in with mineral deposits, which would
have been harder than the surrounding rocks. As those surrounding rocks
eroded away over millions of years, the seams of mineral-hardened
material would remain in place, forming the ridges seen today.
To test their hypothesis the Brown team mapped over 4,000 ridges in two crater-pocked regions on Mars, Nili Fossae (image above) and Nilosyrtis.
Using high-resolution images from NASA’s Mars Reconnaissance Orbiter,
the researchers noted the orientations of the ridges and composition of
the surrounding rocks.
The orientation data is consistent with the idea that the ridges
started out as fractures formed by impact events. A competing hypothesis
suggests that these structures may have been sheets of volcanic magma
intruding into the surrounding rock, but that doesn’t appear to be the
case.
At Nili Fossae, the orientations are similar to the alignments of
large faults related to a mega-scale impact. At Nilosyrtis, where the
impact events were smaller in scale, the ridge orientations are
associated with each of the small craters in which they were found.
“This suggests that fracture formation resulted from the energy of
localized impact events and are not associated with regional-scale
volcanism,” Brown team member, Lee Saper said.
Importantly also found that the ridges exist exclusively in areas
where the surrounding rock is rich in iron-magnesium clay, a mineral
considered to be a telltale sign that water had once been present in the
rocks.
“The association with these hydrated materials suggests there was a
water source available,” Saper added.
“That water would have flowed
along the path of least resistance, which in this case would have been
these fracture conduits.”
As that water flowed, dissolved minerals would have been slowly
deposited in the conduits, in much the same way mineral deposits can
build up and eventually clog drain pipes. That mineralized material
would have been more resistant to erosion than the surrounding rock. And
indeed, Saper and Mustard found that these ridges were only found in
areas that were heavily eroded, consistent with the notion that these
are ancient structures revealed as the weaker surrounding rocks were
slowly peeled away by wind. Taken together, the results suggest the
ancient Martian subsurface had flowing water and may have been a
habitable environment.
“This gives us a point of observation to say there was enough
fracturing and fluid flow in the crust to sustain at least a regionally
viable subsurface hydrology,” Saper said. “The overarching theme of
NASA’s planetary exploration has been to follow the water. So if in fact
these fractures that turned into these ridges were flowing with
hydrothermal fluid, they could have been a viable biosphere.”
Saper hopes that the Curiosity rover, currently making its way across its Gale Crater landing site, might be able to shed more light on these types of structures.
“In the site at Gale Crater, there are thought to be mineralized
fractures that the rover will go up and touch,” Saper said. “These are
very small and may not be exactly the same kind of feature we studied,
but we’ll have the opportunity to crush them up and do chemical analysis
on them. That could either bolster our hypothesis or tell us we need to
explore other possibilities.”
The research was supported by a grant from NASA’s Rhode Island Space Grant Consortium and through a NASA subcontract with the Applied Physics Lab at Johns Hopkins University.
Image Credit: NASA and Mustard Lab/Brown University
Source: The Daily Galaxy via Brown University
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