Curiosity finds 'stream gravel' on Mars
01 October 2012, 09:41
Washington - Nasa's Mars rover has discovered gravel
once carried by the waters of an ancient stream that "ran vigorously"
through the area, the US space agency said.
previously found other evidence of the one-time presence of water on the
Red Planet, but this is the first time stream bed gravel has been
The rocky Hottah outcrop looks "like someone
jack-hammered up a slab of city sidewalk, but it's really a tilted block
of an ancient stream bed", project scientist John Grotzinger said in a
The Curiosity rover, which has been exploring Mars since early August, also investigated a second outcrop known as Link.
pictures transmitted by Curiosity show the pebbles have been cemented
into layers of conglomerate rock at a site between the north rim of the
Gale Crater and the base of Mount Sharp, where Curiosity is heading.
The sizes and the shapes of the rocks give an idea of the speed and the depth of the stream, Nasa said.
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 scientist Rebecca Williams.
Scientists estimate the water was moving at a brisk pace of one metre per second, somewhere between ankle and hip deep.
is the first time we're actually seeing water-transported gravel on
Mars," said Curiosity science co-investigator William Dietrich of the
University of California, Berkeley.
"This is a transition from speculation about the size of streambed material to direct observation of it."
of the rocks are rounded, indicating they travelled a long distance
from above the rim, fed from a channel named Peace Vallis, Nasa said.
thanks to imagery previously captured from Mars's orbit, the scientists
said they can see an alluvial fan of material washed down from the rim -
with many apparent channels uphill of Link and Hottah.
number of channels between the rim and the newly-discovered rock bed
suggests the stream wasn't a one-time occurrence, but that many streams
flowed or repeated over a long period of time.
Curiosity is on a
two-year mission to investigate whether it is possible to live on Mars
and to learn whether conditions there might have been able to support
life in the past.
The $2.5bn vehicle landed in Gale Crater on 6 August, opening a new chapter in the history of interplanetary exploration.