Mars had chilly ancient past
Using NASA's Curiosity Rover, scientists have found evidence for long-lived lakes. They've also dug up organic compounds, or life's chemical building blocks. The combination of liquid water and organic compounds compels scientists to keep searching Mars for signs of past or present life.
Despite the tantalizing evidence found so far, scientists' understanding of Martian history is still unfolding, with several major questions open for debate. For one, was the ancient Martian atmosphere thick enough to keep the planet warm, and thus wet, for the amount of time necessary to sprout and nurture life? And the organic compounds: are they signs of life or of chemistry that happens when Martian rocks interact with water and sunlight?
In a recent Nature Astronomy report on a multi-year experiment conducted in the chemistry lab inside Curiosity's belly, called Sample Analysis at Mars (SAM), a team of scientists offers some insights to help answer these questions. The team found that certain minerals in rocks at Gale Crater may have formed in an ice-covered lake. These minerals may have formed during a cold stage sandwiched between warmer periods, or after Mars lost most of its atmosphere and began to turn permanently cold.
Gale is a crater the size of Connecticut and Rhode Island combined. It was selected as Curiosity's 2012 landing site because it had signs of past water, including clay minerals that might help trap and preserve ancient organic molecules. Indeed, while exploring the base of a mountain in the center of the crater, called Mount Sharp, Curiosity found a layer of sediments 1,000 feet (304 meters) thick that was deposited as mud in ancient lakes. To form that much sediment an incredible amount of water would have flowed down into those lakes for millions to tens of millions of warm and humid years, some scientists say. But some geological features in the crater also hint at a past that included cold, icy conditions. ■