Sciency Words A to Z: Xerophile

Welcome to a special A to Z Challenge edition of Sciency Words!  Sciency Words is an ongoing series here on Planet Pailly about the definitions and etymologies of science or science-related terms.  In today’s post, X is for:

XEROPHILE

You can’t have life without water.  Everybody knows that, right?  Right?  Well, apparently there are some microorganisms on this planet who didn’t get the memo.

The Atacama Desert in Chile is one of the most un-Earth-like environments on Earth.  It is severely dry.  It almost never rains there, and even when it does it’s a pathetic trickle. And it’s been like this for over a hundred millions years, making the Atacama Desert the oldest continuously arid region in the world.

At this point, the Atacama Desert has been so dry for so long that, chemically speaking, it has more in common with the surface of Mars. Most notably, in my opinion, the toxic perchlorate salts found on Mars are also present in the Atacama—0.4 to 0.6 wt% for Mars compared to 0.3 to 0.6 wt% for the Atacama, according to this article.  A near perfect match!

It was once thought the sands of the Atacama Desert were sterile, and experiments on soil samples seemed to prove it.  However, thanks to “improved extraction protocols,” we now know better.  As reported in this paper, titled “Bacterial diversity in hyperarid Atacama Desert soils,” it seems a great many bacterial species have found their way into the Atacama and adapted to the harsh environment.

In general, organisms that can survive in extreme conditions are known as extremophiles.  The term applies especially well to organisms that actually thrive in environments that should kill them.  There are many subcategories of extremophile, such as:

• Thermophiles: organisms that love extreme heat.
• Barophiles: organisms that love extreme pressure.
• Acidophiles: organisms that love acid.
• Halophiles: organisms that love salt.

Any organism that can survive in the Atacama Desert would be considered a xerophile, which comes from a Greek word meaning dryness.  They’d also probably be halophiles, given the presence of those perchlorate salts.  As noted in this article: “Xerophilic organisms are often also halophilic, some of them occurring in hypersaline solutions.”

So what does all this mean for our chances of finding life on Mars?  I think that should be obvious.  However, it’s worth noting that even xerophiles require some water.  Remember, even in the Atacama Desert it rains a little. Fortunately for any xerophiles who might be eeking out an existence on Mars, there seem to be a few rare trickles of water there too.

Next time on Sciency Words A to Z, have you seen Europa, the moon of Jupiter?  She looks a whole lot younger than she really is.  So what’s her secret?