| Curiosity’s pictures find ancient history of flowing water on Mars!

Mars pebbles prove water history ~ Jonathan Amos, Science correspondent, BBC News.

Scientists now have definitive proof that many of the landscapes seen on Mars were indeed cut by flowing water.

The valleys, channels and deltas viewed from orbit have long been thought to be the work of water erosion, but it is Nasa’s latest rover, Curiosity, that has provided the “ground truth”.

Researchers report its observations of rounded pebbles on the floor of the Red planet’s 150km-wide Gale Crater.

Their smooth appearance is identical to gravels found in rivers on Earth.

Rock fragments that bounce along the bottom of a stream of water will have their edges knocked off, and when these pebbles finally come to rest they will often align in a characteristic overlapping fashion.

Curiosity has pictured these features in a number of rock outcrops at the base of Gale Crater.

It is confirmation that water has played its part in sculpting not only this huge equatorial bowl but by implication many of the other landforms seen on the planet.

“For decades, we have speculated and hypothesised that the surface of Mars was carved by water, but this is the first time where you can see the remnants of stream flow with what are absolutely tell-tale signs,” Dr Rebecca Williams from the Planetary Science Institute, US, told BBC News.

The American space agency first announced the discovery of the pebbles in September last year, barely seven weeks after Curiosity had landed in Gale.

Researchers have since been studying the robot’s pictures in more detail and have now written up a report for Science magazine – the first scholarly paper from the surface mission to make it into print; and the study reinforces the initial interpretation.

Link The team only has pictures from the rover’s main cameras. Attempts will be made to get close-up, high-resolution imagery of Gale’s conglomerates in the weeks ahead using the Mahli “hand lens”.

It describes the nature of the outcrops, and estimates the probable conditions in which their sediments were laid down.

The pebbles range in size from about two to 40mm in diameter – too big to have been blown along by the wind.

These clasts, as scientists will often call them, are cemented together in a sandy matrix to make a rock type referred to as a conglomerate.

In many places, the clasts are touching each other, and the pictures show examples of so-called imbrication – an arrangement where elongated pebbles stack like a row of toppled dominos. It is a classic sign of past river activity.

Precisely dating landforms on Mars is not possible, but the rock outcrops seen by the rover are almost certainly more than three billion years old.

Curiosity’s pictures have enabled the team to make some informed statements about the speed and depth of the water that once flowed across the crater floor.

Reull Vallis
So many surface features look from orbit to have been cut by flowing water.

“We estimate that the flow velocities were walking pace, approximately – it’s not something we can absolutely reconstruct, but it gives us a rough idea, and these are minimum values,” explained Prof Sanjeev Gupta from Imperial College London, UK.

“And we can also say that the water depths ranged from ankle-deep to waist-deep.

“This is the first time we’ve been able to do this quantification [on the Red Planet]. It is routine to do this on Earth, but to do it on Mars by looking at ancient rocks is just remarkable.”

River gravelsAncient river deposits on Earth. Note the predominantly sandy layers. These indicate there was a drop in the speed of the water, meaning only the smallest particles could be carried and deposited downstream.

The pebbles come in a variety of dark and light shades, further indicating that they have been eroded from different rock types and transported from different locations.

Using its Chemcam remote-sensing laser, the rover was able to detect feldspar in the lighter toned clasts.

Feldspar is a common mineral on Earth that weathers quickly in the presence of water.

This suggests past conditions were not overly wet and that the pebbles were carried only a relatively short distance – probably no more than 10-15km.

This fits with satellite observations of what appears to be a nearby network of old rivers or streams spreading away from the mouth of a channel that cuts through the northern rim of Gale Crater.

This valley – or Peace Vallis as it is known – is the probable route down which the water flowed and later dumped its load of rounded gravels.

Curiosity is due to drive back on itself in the coming weeks as it makes for the big peak, Mount Sharp, at the centre of the crater.

Scientists hope this will take the vehicle past similar rock outcrops so that additional pictures can be obtained.

“What’s exciting is that when we made this discovery our highest resolution camera – the hand-lens camera, Mahli – hadn’t even been commissioned. It has now. So, if we find similar rocks on the way to Mount Sharp, we will be able to get much better images with fantastic detail,” said Prof Gupta.

Sanjeev Gupta will be discussing the explorations and discoveries of the Curiosity rover on Mars with astrobiologist Lewis Dartnell at next week’sTimes Cheltenham Science Festival on Sunday 9 June. A huge panorama of Mount Sharp built from Curiosity pictures is going on display at the Visions of the Universe exhibition at the National Maritime Museum in London from Friday 7 June.

Gale Crater

 

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| NASA: Curiosity finds old stream-bed on Mars!

Curiosity Finds Old Streambed on Mars ~  Science@NASA.

NASA’s Curiosity rover mission has found evidence a stream once ran vigorously across the area on Mars where the rover is driving. There is earlier evidence for the presence of water on Mars, but this evidence — images of rocks containing ancient streambed gravels — is the first of its kind.

“From the size of gravels it carried, we can interpret the water was moving about 3 feet per second, with a depth somewhere between ankle and hip deep,” said Curiosity science co-investigator William Dietrich of the University of California, Berkeley. “Plenty of papers have been written about channels on Mars with many different hypotheses about the flows in them. This is the first time we’re actually seeing water-transported gravel on Mars. This is a transition from speculation about the size of streambed material to direct observation of it.”

Martian Streambed (splash)

NASA’s Curiosity rover found evidence for an ancient, flowing stream on Mars at a few sites, including the rock outcrop pictured here, which the science team has named “Hottah” after Hottah Lake in Canada’s Northwest Territories. Image credit: NASA/JPL-Caltech/MSSS

The finding site lies between the north rim of Gale Crater and the base of Mount Sharp, a mountain inside the crater. Earlier imaging of the region from Mars orbit allows for additional interpretation of the gravel-bearing conglomerate. The imagery shows an alluvial fan of material washed down from the rim, streaked by many apparent channels, sitting uphill of the new finds.

The rounded shape of some stones in the conglomerate indicates long-distance transport from above the rim, where a channel named Peace Vallis feeds into the alluvial fan. The abundance of channels in the fan between the rim and conglomerate suggests flows continued or repeated over a long time, not just once or for a few years.

The discovery comes from examining two outcrops, called “Hottah” and “Link,” with the telephoto capability of Curiosity’s mast camera during the first 40 days after landing. Those observations followed up on earlier hints from another outcrop, which was exposed by thruster exhaust as Curiosity, the Mars Science Laboratory Project’s rover, touched down.

“Hottah looks like someone jack-hammered up a slab of city sidewalk, but it’s really a tilted block of an ancient streambed,” said Mars Science Laboratory Project Scientist John Grotzinger of the California Institute of Technology in Pasadena.

The gravels in conglomerates at both outcrops range in size from a grain of sand to a golf ball. Some are angular, but many are rounded.

“The shapes tell you they were transported and the sizes tell you they couldn’t be transported by wind. They were transported by water flow,” said Curiosity science co-investigator Rebecca Williams of the Planetary Science Institute in Tucson, Ariz.

The science team may use Curiosity to learn the elemental composition of the material, which holds the conglomerate together, revealing more characteristics of the wet environment that formed these deposits. The stones in the conglomerate provide a sampling from above the crater rim, so the team may also examine several of them to learn about broader regional geology.

The slope of Mount Sharp in Gale Crater remains the rover’s main destination. Clay and sulfate minerals detected there from orbit can be good preservers of carbon-based organic chemicals that are potential ingredients for life.

“A long-flowing stream can be a habitable environment,” said Grotzinger. “It is not our top choice as an environment for preservation of organics, though. We’re still going to Mount Sharp, but this is insurance that we have already found our first potentially habitable environment.”

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