A NASA rover's discovery of an ancient streambed on Mars is exciting, but it’s far from the first solid evidence that the Red Planet was once a warmer and wetter place. On Thursday (Sept. 27), scientists announced that the Curiosity
rover had found rocky outcrops containing large and rounded stones
cemented in a conglomerate matrix. The discovery suggests that water had flowed fast and relatively deep — perhaps hip-deep, in fact — through the area billions of years ago.
But Curiosity's find didn't exactly surprise mission scientists. They chose to set the $2.5 billion robot down in the Red Planet's
huge Gale Crater, after all, because Mars-orbiting spacecraft have
spotted signs there of long-ago water activity — from channels and
alluvial fans to minerals that form in the presence of liquid water.And these more recent observations build on evidence for a wet ancient
Mars that goes back four decades and has been accumulating ever since.
Curiosity's mission may also shed light on when and why Mars dried out
long ago. Scientists plan to drive the 1-ton robot partway up Mount
Sharp, which rises 3.4 miles (5.5 kilometers) into the Red Planet sky
from Gale's center. They're keen to explore Mount Sharp's base, which harbors clays and
sulfates, orbital observations have shown. About 2,300 feet (700 meters)
up, however, these deposits peter out. If Curiosity climbs high enough
to cross this threshold, it could help scientists piece together a
history of wet Mars, dry Mars and the transition between the two,
researchers have said. Space.com
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