Transcripts of movie

[00:00:00.04] [Music]
[00:00:09.07] Carolyn Crow: So far we've found more than 400 planets around other stars.
[00:00:13.10] Unfortunately, for many years to come, we won't be able to see them as anything more than dim
[00:00:17.13] points of light. If only the planets that we know best could help us
[00:00:21.20] learn more about the real worlds behind those dim points of light.
[00:00:25.27] Well it turns out they can. Remember the Deep Impact mission?
[00:00:29.45] The NASA spacecraft that slammed a probe into a comet in 2005?
[00:00:33.48] Well now it's headed for another comet. While on its way we used its
[00:00:37.50] instruments to study the amount of red, green, and blue light reflected
[00:00:41.52] by Earth, the Moon, and Mars. Combining this color information
[00:00:45.56] with similar studies of the other planets in our solar system, we found an interesting
[00:00:49.58] pattern. These crosshairs mark the spot where
[00:00:53.61] a planet would perfectly reflect all the light from the Sun. The more
[00:00:57.64] red light a planet reflects, the farther it moves to the right on this chart.
[00:01:01.66] The more blue light it reflects, the higher it goes. And if the
[00:01:05.68] planet reflects relatively little blue and red light, it falls in the dark
[00:01:09.86] section. Viewed in this way, here's
[00:01:13.87] where the planets lie.
[00:01:21.92] Not surprisingly, Mars, the reddest planet, occupies the reddest spot.
[00:01:25.94] Mercury is also nearby on the plot because neither planet has a large
[00:01:29.98] atmosphere that scatters blue light. Venus has a thick cloudy atmosphere
[00:01:34.00] that reflects most of the red light and only a little bit
[00:01:38.04] of the blue light, so it stays near the bottom. Jupiter and Saturn fall in the darkest
[00:01:42.07] region of the plot. Their atmospheres have methane and ammonia in it, which
[00:01:46.12] absorbs red light and other gasses that absorb blue light.
[00:01:50.13] Here's what's really interesting. In this chart, Earth stands apart
[00:01:54.29] from all the other planets. Earth is
[00:01:58.31] really blue. Not because of its oceans, but because it has an atmosphere that reflects
[00:02:02.34] a lot of blue light. It makes sense, that's why the sky is blue.
[00:02:06.37] At the same time, Earth does reflect a little bit of red light.
[00:02:10.40] Long before we have telescopes that will show us what extrasolar
[00:02:14.44] planets really look like, we'll be able to measure their colors and put them on the plot.
[00:02:18.48] This means we'll be able to tell the difference between alien
[00:02:22.52] versions of Mars, Jupiter, and even Earth. And that's
[00:02:26.57] something we're looking forward to. [Music]
[00:02:33.58] [Beeping]