
One of Mars’s resident robots, NASA’s Curiosity rover, has just made a discovery that up-ends scientific expectations. It has found something that scientists believe simply “should not be there.”
The rover, which has a curb weight of around a full ton, is on a mission to uncover chemical evidence that the red planet might once have been hospitable to life. As part of that search it has recently struck gold—or, at least, yellow. Specifically, Curiosity has happened upon a cache of crystals with a yellowy-green hue, which its on-board instrumentation has identified as pure sulfur.
The discovery happened when Curiosity, as it was traveling through the Gediz Vallis channel, accidentally cracked open some white stones, revealing the strange crystalline deposits within.
Sulfur, itself, has never been a stranger to Mars as a component in chemical compounds, but thus far it has never been observed there in its elemental form. The presence of elemental sulfur is just one more grain of evidence on the side of the scale suggesting that Mars was, at some point in its history, a habitable planet.
As revealed in previous laboratory experiments, by analysis of Earth’s ancient atmosphere as captured in fossil records, and through studies of chemo-synthetic life forms near deep-ocean hydro-thermal vents here on Earth, elemental sulfur seems to be a key ingredient in the formation of life as we know it. On ancient Earth, volcanic activity routinely released various isotopes of sulfur into the atmosphere, where it was fed upon by bacteria that subsequently released oxygen into the atmosphere as a waste product, laying the groundwork for the world we now live in.
However momentous this new discovery, scientists are quick to caution that habitable and inhabited are not the same thing. The emerging picture of ancient Mars is one that, being rich in water, phosphorous, carbon, and iron, might have played host to life, but scientists don’t yet know enough about how life emerges to confidently declare that it once existed there.