This is planetary radio. Matt Kaplan welcoming you to this week's edition of our show, everywhere we look on Earth, even in the most extreme environments,

we find life, not just life, but whole ecosystems

where scientists once thought it impossible.

Our guest this week, NASA planetary scientist Chris McKay, has been to an amazing number of these

extreme locales, always wondering if the even more extreme conditions on Mars have allowed life

to eke out a similar existence.

He has devoted his adult life to that question, and he'll share his thoughts with us.

Later on what's up Bruce Betts will put us between a rock and a hard place with this week's

trivia question.

But first Emily provides some background for our discussion of the Martians that may be.

I'll be back with Chris McKay in a minute. Hi, I'm Emily Lochuwala with questions and answers. A listener asked, how could there be life on Mars

if there's no water or air? Mars is a pretty inhospitable place. The daily surface

temperature swings from a freezing minus 5 Celsius during the day to a desperately cold minus 85 at night.

The atmosphere is so thin that except at the frigid poles, any water or ice exposed on the surface would rapidly boil away into vapor.

This may not always have been the case.

There's lots of geological evidence that Mars could once have been a warmer and wetter place.

But under present conditions, Earth-like life exposed to the surface of Mars would be instantly freeze-dried.

So even if life once existed on Mars, it doesn't seem likely that there can be anything living there today.

At least that's what we used to think.

But recent discoveries of organisms on Earth, called extremophiles, have given some scientists

hope that there could still be life not on Mars, but in Mars. How is this possible?

Stay tuned to Planetary Radio to find out. Chris McKay, thanks for joining us on planetary radio.

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