NASA's Opportunity rover has been on Mars for nearly 3,000 days out of its originally scheduled 90-day mission. It's currently on its fifth Martian winter, and its solar panels are getting so dusty that the reduced daylight and low sun angle are threatening to starve the rover for power. Since a helpful rain shower seems like a long shot, Oppy is hoping to instead get hit by a tornado.

Mars500, a 520-day simulation conducted by the European Space Agency and Russia's Roscosmos, wrapped up late last year. Mars500 took place here on Earth; NASA, looking to conduct a similar test, is thinking of taking the project onto the International Space Station for more accurate conditions.

Antarctica isn't completely covered in ice. The McMurdo Dry Valleys almost never see rain and look like a barren desert. Yet photos of the area show patches of moisture on the ground, and geologists believe the soil is wicking moisture out of the atmosphere — which could be happening on seemingly dry planets, too.

The driest desert on earth — the Atacama Desert of Peru — is considered a great stand in for what the geology of Mars is like. It's no wonder then that scientists are excited to find what they term an "oasis" of micro-organisms living under the surface of the desert. Such a find could mean that similar microbes could theoretically exist under the surface of Mars.