Evidence gathered by NASA's Curiosity Rover during its 2-year-plus study of soil and rocks in Gale Crater points to a startling conclusion: this 96-mile-wide crater once held a lake some 900 feet deep.
Mount Sharp, the crater's broad central peak, stands about 3 miles (5 km) tall and was built by sediments deposited in the lake over tens of millions of years by wind, rivers and material settling to the lake bottom. Curiosity is currently investigating the lower 500 feet (150-meters) of sedimentary rock at the base of the mountain where hundreds of layers of rock are exposed like so many layers of a Vienna torte.
ADVERTISEMENT
All this activity occurred an estimated 3 billion years ago when the atmosphere of Mars had to be much denser than it is today. For water to exist out in the open on a planet, sufficient atmospheric pressure is needed to prevent it from vaporizing into thin air. Literally. Mars' atmospheric pressure today is 1/1000 that of Earth, much too tenuous to keep water down.
"We are making headway in solving the mystery of Mount Sharp," said Curiosity Project Scientist John Grotzinger of the California Institute of Technology in Pasadena. "Where there's now a mountain, there may have once been a series of lakes."
Only problem is, scientists still can juggle the models to arrive at a satisfactory explanation for why the Martian climate was so radically different in the distant past. Hypotheses abound. Was it the decay of the planet's magnetic field and stripping of its atmosphere by the solar wind or did intense asteroid bombardment send it flying into the vacuum of space?
Whatever happened, over time, the water evaporated, vaporized or seeped away, and sediments hardened into rock. Winds howling for hundreds of millions of years carved away at the material between the crater's rim and what is now the edge of the expansive Mt. Sharp, exposing layer upon layer of the crater's past.
"We found sedimentary rocks suggestive of small, ancient deltas stacked on top of one another," said Curiosity science team member Sanjeev Gupta of Imperial College in London. "Curiosity crossed a boundary from an environment dominated by rivers to an environment dominated by lakes."
Scientists are left with a conundrum -- how did Mars produce the conditions that would keep liquid water stable for millions of years, long enough for lakes and rivers to deposit hundreds of feet of sediments? For now, it's just enough to know it happened, and that what appears to be a dusty, rocky depression once held more water than Lake Erie.
ADVERTISEMENT
