Half a mile below the surface of the earth, in a cave too hot to explore without an ice-packed suit, NASA scientist and Nat Geo explorer Penny Boston clambers around glassy crystals that are taller than telephone poles and wider than dinner tables. But it's not The Crystal Cave's grandeur she's interested in -- it's what may be hibernating inside the crystals. Astrobiologists like Penny Boston scour the Earth's most hostile environments for microorganisms, to see if they hold clues to what life might look like on other planets - maybe even planets in our solar system. For more information on this episode, visit nationalgeographic.com/overheard

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Hear Penny Boston speak on stage about her search for extremophiles all over the world.

Inside the Cave of Crystals, Penny Boston discovered organisms that have been alive for tens of thousands of years, trapped inside the crystals.

Kevin Hand has been eager to search for life on Europa for a long time. He's been testing robots in the arctic to see if they can withstand the extreme conditions there.

Europa isn't the only planet with the potential for life. Europa isn't the only planet with the potential for life. Scientists are hunting the galaxy for other planets that are just the right size and temperature. It turns out there may be billions of them.

Also explore:

Watch President Bill Clinton give a speech about the Allan Hills meteorite - a rock from Mars that looked like it might contain fossilized life.

You can see a photo of the strange shapes in the Allan Hills meteorite and read more about why scientists thought those shapes might be signs of life.

Penny Boston is the director of the NASA Astrobiology Institute. They're working hard to study what alien life might be like.

Kevin Hand is part of a team of scientists who are building the Europa Clipper - a probe designed to search the moon orbiting Jupiter for the right conditions for life.

Europa has a huge liquid water ocean. Here's more information from Kevin Hand about why that ocean might be inhabited.

If you like what you hear and want to support more content like this, please consider a National Geographic subscription. Go to natgeo.com/exploremore to subscribe today. 

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