Narrator
Listen to part of a lecture in an Astronomy Class
Professor:
Last week, we covered some arguments against going back to the Moon. But
there are compelling reasons in favor of another Moon landing too, um… not
the least of which is trying to pinpoint the moon’s age. We could do this in
theory by studying an enormous impact crater, known as the South
Pole-Aitken Basin. Um…it’s located in the moon’s South Polar Region. But,
since it’s on the far side of the moon, it can only be seen from space. Here is
an image of…we’ll call it the SPA Basin. This color-coated image of the SPA
Basin, those aren’t its actual colors obviously, this image is from the mid 90s,
from the American spacecraft called Clementine. Um… unlike earlier lunar
missions, Clementine didn’t orbit only around the moon’s equator. Its orbits
enable it to send back data to create this topographical map of … well, the grey
and white area towards the bottom is the South Pole, the purples and blues in
the middle correspond to low elevations - the SPA Basin itself, the oranges
and reds around it are higher elevations. The basin measures an amazing
2,500 km in diameter, and its average depth is 12 km. That makes it the
biggest known crater in our solar system and it may well be the oldest.
You know planetary researchers love studying deep craters until learn about
the impacts that created them, how they redistributed pieces of a planet’s crust
and in this case, we especially want to know if any of the mantle, the layer
beneath the crust, was exposed by the impact. Not everyone agrees, but some
experts are convinced that whatever created the SPA Basin did penetrate the
Moon’s mantle. And we need to find out, because much more than the crust,
the mantle contains information about a planet’s or Moon’s total composition.
And that’s key to understanding planet formation. Um… Dian?
Dian: So, the only way to know the basin’s age is to study its rocks directly?
Professor: well, from radio survey data, we know that the basin contains lots of
smaller craters. So it must be really old, about 4 billion years, give or take a
few hundred million years. But that’s not very precise. If we had rock samples
to study, we’d know whether the small craters were formed by impacts during
the final stages of planetary formation, or if they resulted from later meteor
showers.
Dian: But if we know around how old the Basin is, I’m not sure that’s reason
enough to go to the Moon again.
Professor: No…, but such crude estimates…um…we can do better than that.
Besides, there are other things worth investigating, like is there water ice on
the moon? Clementine’s data indicated that the wall of the south-polar crater
was more reflective than expected. So some experts think there’s probably ice
there. Also, data from a later mission indicates significant concentrations of
hydrogen and by inference water less than a meter underground at both poles.
Student: Well if there’s water, how did it get there? Underground rivers?
Professor: We think meteors that crashed into the moon or tails of passing
comets may have introduced water molecules. Any water molecules that found
their way to the floors of craters near the moon’s poles, that water would be
perpetually frozen, because the floors of those craters are always in shadow.
Um…furthermore, if the water ice was mixed in with rock and dust, it would be
protected from evaporation.
Dian: So are you saying there might be primitive life on the moon?
Professor: that’s not my point at all. Um… o.k., say there is water ice on the
moon. That would be a very practical value for a future moon base for
astronauts. Water ice could be melted and purified for drinking. It could also be
broken down into its component parts - oxygen and hydrogen. Oxygen could
be used to breathe, and hydrogen could be turned into fuel, rocket fuel. So
water ice could enable the creation of a self-sustaining moon base someday, a
mining camp perhaps or a departure point for further space exploration.
Student: But holding tons of equipment to the moon to make fuel and build a
life support system for a moon base, wouldn’t that be too expensive?
Professor: Permanent base, maybe a way’s off, but we shouldn’t have to wait
for that. The dust at the bottom of the SPA Basin really does have a fascinating
story to tell. I wouldn’t give for a few samples of it.