Red marked places are the mistakes i made when i recorded it.
Listen to part of a lecture
in an astronomy class.
I’m sure you all have been following the news about the Mars. A lot of spacecraft have been visiting the planet recently- some have
gone into orbit around it, well, while others have landed on it. 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. Is there anything that you’ve been particularly struck by in all the news reports?
Well, they seem to mention
water a lot, which kind of surprised me as I have this picture in my head that
Mars is dry… sort of dry and dead.
You are not the only one.
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. When the first science-fiction came out, Mars was described
as being a lot like Earth except…
I know that the planet was red and, uh, the
people are green. I’ve seen some of those old
movies. What were they thinking? I mean, really… they…
Well, it seems silly to us now but those ideas were quite imaginative and, occasionally, scary in their time.
Anyway, we began to rethink our image of Mars when the first spacecraft flew by the planet in
1965 and sent some pictures back to earth. Those pictures showed a planet that looked a lot more like our moon than earth- lots of craters
and not much else. It was bitterly code. It had
a very thin atmosphere. And that atmosphere was mostly carbon
dioxide. So, the view of Mars after this first flyby mission was that dry, dead
planet that Lisa mentioned. But then there were
more visitors to the planet in the 1970s - and this time the spacecraft didn’t just fly by, they orbited or landed.
This allowed us to receive more detailed images
of the planet, and it turned out to be a pretty interesting
place. Mars had… has a
lot more than craters, it has giant volcanoes and
deep canyons. It also showed signs of dried-up riverbeds
and plains that had been formed by massive floods. So we can concluded
that there must have been water on the planet at
one time, billions of years ago. Now, what does it take for water to exist?
You need to have a warm enough temperature so that it doesn’t to freeze.
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. The Mars
we see today doesn’t have either of those conditions.
It’s 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. So, maybe Mars wasn’t just a dead boring rock. Maybe it was a fascinating
fossil that once was alive in dynamic – worthy of
exploration. 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. Of
course the scientific instruments now surveying Mars
are far more sophisticated than the
instruments of the 70’s. So we are getting all kinds of new data for analysis. And
not surprisingly, that data is challenging our notions of what Mars is like. Lisa,
you mentioned that a lot of the news reporters talked about water. Do you remember any
of the details?
Well, they are showing these pictures with these long, uh, cuts in the
ground which would be gullies here. I mean, on earth. 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.
I’m not surprised. There are
a lot of theories, a lot of that speculation. Some argue that the formations aren’t caused by water at all. But
there are some ingenious theories that assume there’s
a lot of water right under the planet’s surface that is
somehow causing the gullies to form. If only we can get a lander there… but gullies aren’t in places
where we can send landers yet. Anyway, if there is some kind of water activity,
it may change our view of the planet once again… to something that is 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. Maybe Mars can sustain
water again at some distant date.
No comments:
Post a Comment