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| Titan's frozen lakes |
Saturn's moon Titan, which Sagan describes as noteworthy for the presence of proto-organic molecules but shrouded within a dense atmosphere, has had its cloud-cover penetrated by radar and other sensing devices aboard the Cassini probe, which also launched a small lander named Huygens. The probe brought back remarkable images of the lakes of liquid methane and ethane that dot the surface, and Huygens brought back visual imagery of its surface; Titan is now the furthest object in our solar system that we've landed on. We've even been able to make time-lapse videos
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| The surface of Titan |
In the case of Uranus, we haven't learned that much more since Sagan's book, though we now know that its rocky core, much like that of more-distant Neptune, is smaller and more compact than Sagan imagined. It's tricky to infer the content of a gas-cloaked giant; one can discover its mean density easily enough, but calculating where the layers start and end requires measuring other forms of radiation than light, and close observation of rotational and seasonal variations.
In the case of now-demoted Pluto, we've been extraordinarily fortunate in that NASA's New Horizons probe, launched it 2006, reached its intended destination in nine years; it has provided remarkably detailed imagery of Pluto, and particularly dramatic view of Pluto's moon Charon. At this remote distance from the sun, of course, it's far too cold for any expectation of life, but remarkably enough there were conditions on Pluto that at one time enabled the building of proto-organic compounds similar to those found on Titan. These compounds also shared a color, a sort of orangey brown, and New Horizons found that Charon -- much bigger in proportion to its planet than any other moon in our solar system -- apparently performed a sort of gravitational robbery of these compounds from the parent planet; they stained a large area near Chiron's pole, a distinctive feature dubbed "Mordor" by NASA's scientists.
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| Charon |
