Round pebbles confirm Mars once had rivers
UNITED STATES
THE LANDING site of the Mars rover Curiosity was once covered with fast-moving and possibly waist-high water that could have possibly supported life, Nasa scientists have revealed.
While planetary scientists have often speculated that the nowdesiccated surface of Mars was once wet, Curiosity cameras provided the first proof that flowing water was present on a least one part of Mars for ‘‘thousands or millions of years’’.
The early finding led Mars Science Laboratory mission top scientist John Grotzinger to conclude that Curiosity had already found a potentially ‘‘habitable’’ site – a central goal of the mission – well before heading to its primary destination.
While the area may not have other attributes needed for life, he said, the team now has a ‘‘hall pass’’ on the question of flowing water, and the Gale Crater landing site seemed even more appealing.
‘‘A long-flowing stream can be a habitable environment,’’ he said.
This photo, taken by Curiosity, shows the Martian rock outcrop the rover team has named Hottah. The formation, which looks like a broken sidewalk, shows evidence of an ancient stream and led scientists to believe that they may have identified a potentially habitable environment on the planet. ‘‘We’re still going to Mount Sharp [a 4828-metre high mound at the centre of the crater] but this is insurance that we have already found our first potentially habitable environment.’’
Curiosity team scientists determined that flowing water was once present near the Gale Crater landing site based on the telltale size, shape and scattering of
In this image, the Link, left, an outcrop of rocks on Mars, is compared with rocks on Earth. The image of the Mars rock formation was obtained by NASA’s Curiosity rover. Both images show rounded gravel fragments called clasts. Erosion of the outcrop results in the gravel clasts, which fall on to the ground and create a gravel pile like the one seen. pebbles and gravel nearby, especially those found in conglomerate rocks at three different sites.
The roundedness of the pebbles is especially significant, they said, and strongly suggest that the rocks were carried down a roughly 32 to 40 kilometre stream or river and were smoothed along the way.
William Dietrich, professor of geomorphology and member of the Curiosity imaging science team, presented some rounded earthly pebbles, which he said are similar to those found in the images.
‘‘Plenty of papers have been written about channels on Mars, with many different hypotheses about the flows in them,’’ Dietrich said.
‘‘This is the first time we’re actually seeing water-transported gravel on Mars. This is a transition from speculation about the size of stream-bed material to direct observation of it.’’
Curiosity made its dramatic landing early August, and has spent much of its time since testing out systems and instruments and preparing for its two-year drive.
But the rover’s suite of cameras began sending back images of the conglomerate rock with small pebbles soon after landing, and they provided sufficiently detailed pictures to convince scientists that the pebbles and gravel had a watery past.
Gale Crater was selected as a landing site in part because satellite imaging had earlier found what appeared to be a sizeable cut in the crater wall that looked like a dried river or stream bed.
The bed continued into the crater and then spread out in the shape of a delta. Similar features have been found in many other Martian locations.
The Curiosity team thought the rover had not landed exactly on that dried delta – or ‘‘alluvial fan’’ as geologists describe it – but the finding of the water-borne rocks is forcing them to rethink the size of the fan.
Ironically, the confirmation of Martian water flows came in the early days of a mission that had very consciously discarded the long-standing Nasa directive to ‘‘follow the water’’ in Mars exploration.
While finding and studying the signatures of past water flows is important for Curiosity’s goal of identifying habitats that could have supported life, the mission motto is now ‘‘follow the carbon’’.
That element is present in all organic compounds, which are the building blocks of life on Earth and are expected to have been similarly essential to any possible Martian life.
Curiosity has two miniature chemistry labs that will test for those organic compounds and other telltale elements.
The rover’s ultimate destination is the mound in the centre of the crater, but it will first detour to a nearby and unusual geological meeting of three rock types — including one at the very end of the fan. Scientists think that rock may well be formed from fine clays, the lightest material carried by the water and so the last to drop out.
Announcement of the long-ago presence of Martian surface water is an early coup for the mission, but is consistent with the rover’s unusually good fortunes.
Since making its near-perfect landing, the rover’s major systems and instruments have all checked out successfully. There have been a few glitches — wind sensors for the weather station were damaged at landing and unwanted Florida air was discovered in some instruments – but Nasa officials foresee no lasting obstacles.