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31 May 2013 Last updated at 13:01 Share this
Mars pebbles prove water historyJonathan Amos
By Jonathan Amos
Science correspondent, BBC News
http://news.bbcimg.co.uk/media/images/67875000/jpg/_67875682_outcrop.jpg
Hottah Curiosity saw a series of outcrops containing gravels cemented together in a sandy matrix
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.
http://news.bbcimg.co.uk/media/images/67875000/jpg/_67875684_link.jpg
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 imager 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."
http://news.bbcimg.co.uk/media/images/67909000/jpg/_67909359_67909358.jpg
So many surface features look from orbit to have been cut by flowing water
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.
http://news.bbcimg.co.uk/media/images/67875000/jpg/_67875509_slide144.jpg
Ancient 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
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.
7hK57--WeC8
Sanjeev Gupta will be discussing the explorations and discoveries of the Curiosity
rover on Mars with astrobiologist Lewis Dartnell at next week's Times 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.
http://news.bbcimg.co.uk/media/images/67875000/jpg/_67875686_gale.jpg
Gale Crater
Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos
http://www.bbc.co.uk/news/science-environment-22708902
http://static.bbci.co.uk/frameworks/barlesque/2.45.9/desktop/3.5/img/blq-blocks_grey_alpha.png
31 May 2013 Last updated at 13:01 Share this
Mars pebbles prove water historyJonathan Amos
By Jonathan Amos
Science correspondent, BBC News
http://news.bbcimg.co.uk/media/images/67875000/jpg/_67875682_outcrop.jpg
Hottah Curiosity saw a series of outcrops containing gravels cemented together in a sandy matrix
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.
http://news.bbcimg.co.uk/media/images/67875000/jpg/_67875684_link.jpg
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 imager 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."
http://news.bbcimg.co.uk/media/images/67909000/jpg/_67909359_67909358.jpg
So many surface features look from orbit to have been cut by flowing water
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.
http://news.bbcimg.co.uk/media/images/67875000/jpg/_67875509_slide144.jpg
Ancient 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
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.
7hK57--WeC8
Sanjeev Gupta will be discussing the explorations and discoveries of the Curiosity
rover on Mars with astrobiologist Lewis Dartnell at next week's Times 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.
http://news.bbcimg.co.uk/media/images/67875000/jpg/_67875686_gale.jpg
Gale Crater
Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos
http://www.bbc.co.uk/news/science-environment-22708902