KELLY MCEVERS, HOST:
The late David Bowie sang about a lot of other worldly things, things like spiders from Mars.
(SOUNDBITE OF SONG, "ZIGGY STARDUST")
DAVID BOWIE: (Singing) Ziggy played guitar, jamming good with Weird and Gilly and the spiders from Mars.
MCEVERS: So it turns out there are spiders on Mars - kind of.
ARI SHAPIRO, HOST:
To explain, we turned to Candice Hansen Koharcheck.
CANDICE HANSEN KOHARCHECK: I work for NASA. I am a planetary scientist, and I work with the camera team on the Mars Reconnaissance Orbiter.
MCEVERS: She explains that Mars has seasonal polar caps similar to the Earth. But unlike the Earth, the ones on Mars are made of carbon dioxide - dry ice.
KOHARCHECK: If you've ever played with dry ice you know how it goes from a solid to a gas directly. It never really melts.
MCEVERS: So when the season changes and the polar cap warms, this dry ice turns to gas. The gas underneath the ice is under huge amounts of pressure and bursts out wherever there are weak spots.
(SOUNDBITE OF SONG, "ZIGGY STARDUST")
BOWIE: (Singing) So where were the spiders?
SHAPIRO: We're getting there. Scientists think that escaping gas picks up bits of dirt and carves channels into Mars's surface. Those formations of channels branching out from a central point are known as spiders.
MCEVERS: Spiders on Mars.
SHAPIRO: Spiders of Mars.
MCEVERS: Hansen Koharcheck says we don't have anything quite like them on our planet.
KOHARCHECK: These terrains on Mars are really very unearthly. And I think that you could say that about David Bowie's music, too.
(SOUNDBITE OF DAVID BOWIE SONG, "ZIGGY STARDUST")
SHAPIRO: This is NPR News. Transcript provided by NPR, Copyright NPR.