A rock on Mars has just spilled a surprising yellow treasure after Curiosity accidentally cracked through its unremarkable exterior.
When the rover rolled its 899-kilogram (1,982-pound) body
over the rock, the rock broke open, revealing yellow crystals of elemental
sulfur: brimstone. Although sulfates are fairly common on Mars, this is the
first time sulfur has been found on the red planet in its pure elemental form.
What's even more exciting is that the Gediz Vallis Channel,
where Curiosity found the rock, is littered with rocks that look suspiciously
similar to the sulfur rock before it got fortuitously crushed – suggesting
that, somehow, elemental sulfur may be abundant there in some places.
"Finding a field of stones made of pure sulfur is like
finding an oasis in the desert," says Curiosity project scientist Ashwin
Vasavada of NASA's Jet Propulsion Laboratory.
"It shouldn't be there, so now we have to explain it.
Discovering strange and unexpected things is what makes planetary exploration
so exciting."
Sulfates are salts that form when sulfur, usually in
compound form, mixes with other minerals in water. When the water evaporates,
the minerals mix and dry out, leaving the sulfates behind.
These sulfate minerals can tell us a lot about Mars, such as
its water history, and how it has weathered over time.
Pure sulfur, on the other hand, only forms under a very
narrow set of conditions, which are not known to have occurred in the region of
Mars where Curiosity made its discovery.
There are, to be fair, a lot of things we don't know about
the geological history of Mars, but the discovery of scads of pure sulfur just
hanging about on the Martian surface suggests that there's something pretty big
that we're not aware of.
Sulfur, it's important to understand, is an essential
element for all life. It's usually taken up in the form of sulfates, and used
to make two of the essential amino acids living organisms need to make
proteins.
Since we've known about sulfates on Mars for some time, the
discovery doesn't tell us anything new in that area. We're yet to find any
signs of life on Mars, anyway. But we do keep stumbling across the remains of
bits and pieces that living organisms would find useful, including chemistry,
water, and past habitable conditions.
Stuck here on Earth, we're fairly limited in how we can
access Mars. Curiosity's instruments were able to analyze and identify the
sulfurous rocks in the Gediz Vallis Channel, but if it hadn't taken a route
that rolled over and cracked one open, it could have been sometime until we
found the sulfur.
The next step will be to figure out exactly how, based on
what we know about Mars, that sulfur may have come to be there. That's going to
take a bit more work, possibly involving some detailed modeling of Mars's
geological evolution.
Meanwhile, Curiosity will continue to collect data on the
same. The Gediz Vallis channel is an area rich in Martian history, an ancient
waterway whose rocks now bear the imprint of the ancient river that once flowed
over them, billions of years ago.
Curiosity has drilled a hole in one of the rocks, taking a
powdered sample of its interior for chemical analysis, and is now trundling its
way deeper along the channel, to see what other surprises might be waiting just
around the next rock.