[00:00.00]Listen to part of a lecture in an astronomy class.
[00:04.24]Professor: I’m sure y'all have been following the news about Mars. [00:07.29]A lot of spacecraft have been visiting the planet recently-some have gone into orbit around it, while others have landed on it. [00:15.46]And, they’ve sent back a ... an abundance of data that’s reshaping our knowledge ... our vision of the planet in a lot of ways. [00:24.11]Is there anything that you've been particularly struck by in all the news reports?
[00:29.18]Female Student: Well, they seem to mention water a lot, which kinda surprised me, as I have this picture in my head that Mars is dry ... sorta dry and dead.
[00:39.16]Professor: You're not the only one. [00:40.77]You know, for centuries, most of our knowledge of the planet came from what we saw through telescopes, so, obviously, it was pretty limited-and our views of the planet were formed as much by writers ... as they were by serious scientists. [00:56.17]When the first science-fiction stories came out, Mars was described as being a lot like Earth except
[01:03.38]Male Student: I know: the planet was red and, uh, the people were green. [01:07.67]I’ve seen some of those old movies, [01:09.89]what were they thinking? [01:11.17]I mean really ... they...
[01:12.58]Professor: Well, it seems silly to us now, but those ideas were quite imaginative and, occasionally, scary in their time. [01:21.44]Anyway, we began to rethink our image of Mars when the first spacecraft flew by the planet in 1965 and sent pictures back to Earth. [01:31.43]Those pictures showed a planet that looked a lot more like our Moon than Earth-lots of craters and not much else. [01:39.61]It was bitterly cold, it had a very thin atmosphere, and that atmosphere was mostly carbon dioxide. [01:48.15]So the view of Mars after this first flyby mission was that dry, dead planet that Lisa mentioned.
[01:55.58]But, then there were more visits to the planet in the 1970s-and this time the spacecraft didn't just fly by; they orbited ... or landed. [02:05.77]This allowed us to receive much more detailed images of the planet and it turned out to be a pretty interesting place. [02:13.88]Mars had ... has a lot more than craters-it has giant volcanoes and deep canyons. [02:23.01]It also showed signs of dried-up riverbeds and plains that had been formed by massive floods. [02:29.35]So we concluded that there must have been water on the planet at one time-billions of years ago. [02:36.18]Now, what does it take for water to exist?
[02:40.18]Male Student: You need to have a warm-enough temperature so that it doesn't freeze.
[02:43.60]Professor: That's one thing-and the other is that you need enough atmospheric pressure, thick-enough air so that the water doesn't instantly vaporize. [02:52.73]The Mars we see today doesn't have either of those conditions-it is too cold and the air is too thin-but a long time ago, there may have been a thicker atmosphere that created a greenhouse effect that raised temperatures-and maybe that combination produced water on the surface of the planet. [03:13.35]So maybe Mars wasn't just a dead, boring rock; maybe, it was, uh, a fascinating fossil that was once alive and dynamic-worthy of exploration, [03:26.47]Now let's jump forward a few decades to the beginning of this century, and a new generation of orbiters and landers that have been sent to Mars. [03:37.04]Of course, the scientific instruments now surveying Mars are far more sophisticated than the instruments of the '70s, so we're getting all kinds of new data for analysis. [03:47.75]And, not surprisingly, that data is challenging our notions of what Mars is like. [03:53.85]Lisa, you mentioned that a lot of the news reports talked about water-do you remember any of the details?
[04:01.18]Female Student: Well, they were showing these pictures of these long, uh, cuts in the ground, which would be gullies here; I mean on Earth. [04:08.99]They say that since, uh, gullies are usually formed by water, it seems like they might be evidence that water still exists on Mars, but I didn't get how that worked.
[04:21.28]Professor: I’m not surprised. [04:22.84]There’re a lot of theories …a lot of speculation …and some argue the formations aren't caused by water at all. [04:31.79]But there're some ingenious theories that assume that there’s a lot of water right under the planet’s surface that somehow is causing the gullies to form. [04:42.13]If we could only get a lander there... but the gullies aren't in places where we can send landers yet. [04:48.97]Anyway, if there is some kind of water activity, it may change our view of the planet once again ... to something that's not dead, not even a fossil, but rather a planet like Earth that undergoes cycles-think of our ice ages-over long periods of time. [05:07.67]Maybe Mars could sustain water again at some distant date.
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