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Titan and the Cassini Saturn tour
Dec. 1st, 2004 08:03 pmOn its last flyby, with its ISS and VIMS instruments, the Cassini Saturn probe got some nice infrared pictures of the portions of Saturn's large moon Titan known as Xanadu and the Sickle. With Cassini approaching Titan for another flyby in a week and a half, I was wondering if we'd get better pictures of the rest of the moon, with the features first seen by the Keck Telescope and ESO Very Large Telescope, and called the Lying H, Dog and Ball, and the Dragon's Head by ESO astronomers.
I investigated this by playing around with computer simulations, and unfortunately, it doesn't appear that we'll get those for some time, at least not in the infrared. Cassini makes its own illumination for radar observations, but for these infrared pictures it needs to be looking at the sunlit side of Titan. So the features that it can photograph at high resolution depend on the sun-Titan geometry at the moment of closest approach.
But Titan, like nearly all moons, is tidally locked so that it always points the same face toward Saturn. So at the same point in its orbit relative to the Sun-Saturn direction, the same part of Titan will always be sunlit. If it stays in a constant elliptical orbit around Saturn, Cassini will always pass Titan at the same point in Titan's orbit relative to the stars. That means that the only way Cassini can get close-approach pictures of other parts of Titan is to either change the geometry of its own orbit, or wait for Saturn to make a significant fraction of its own 29.5-year orbit around the Sun.
Fortunately, the shape, size and orientation of Cassini's orbit is going to change a lot over the next few years (Cassini will mostly use the Titan encounters themselves as the mechanism for the changes). On the next few Titan flybys, we just get more pictures of the Xanadu-Sickle hemisphere. In 2005, though, I think that high-resolution infrared pictures of the Lying H will become possible, then Dog and Ball in 2006 and Dragon's Head in 2007. The most dramatic change will be the maneuver known as the Titan 180 Transfer in late 2006 and early 2007, during which the orbit will mutate and flip around so that it points in a completely different direction; in the meantime Cassini should be capable of taking some exceedingly awesome pictures of Saturn from way above the ring plane.
And, of course, other things are going to be happening, even with regard to Titan. The Huygens probe gets released this Christmas and attempts to land on Titan (in the western Sickle region) on January 14. Also, Cassini doesn't need sunlight to map Titan with radar, though those radar pictures have been even harder to interpret than the infrared ones so far; so far, the only thing that's clear about Titan is that it is a very strange place. I'm looking forward to getting some radar pictures of areas that have already been mapped in the infrared so that it's possible to get context; we might see that soon.
There will also be multiple close approaches to several other moons; I'm particularly looking forward to Iapetus (where Clarke put the big monolith in the book of 2001), Enceladus, Dione, and Hyperion (the only known body in the solar system that rotates chaotically). (That Planetary Society Saturn extravaganza has the best synopses of Pioneer/Voyager/HST/Cassini Saturn exploration that I've ever seen, and it looks as if they're keeping all the moon pages up to date as new pictures come in.)
Meanwhile, the pictures of Saturn and its rings continue to be amazing.
I investigated this by playing around with computer simulations, and unfortunately, it doesn't appear that we'll get those for some time, at least not in the infrared. Cassini makes its own illumination for radar observations, but for these infrared pictures it needs to be looking at the sunlit side of Titan. So the features that it can photograph at high resolution depend on the sun-Titan geometry at the moment of closest approach.
But Titan, like nearly all moons, is tidally locked so that it always points the same face toward Saturn. So at the same point in its orbit relative to the Sun-Saturn direction, the same part of Titan will always be sunlit. If it stays in a constant elliptical orbit around Saturn, Cassini will always pass Titan at the same point in Titan's orbit relative to the stars. That means that the only way Cassini can get close-approach pictures of other parts of Titan is to either change the geometry of its own orbit, or wait for Saturn to make a significant fraction of its own 29.5-year orbit around the Sun.
Fortunately, the shape, size and orientation of Cassini's orbit is going to change a lot over the next few years (Cassini will mostly use the Titan encounters themselves as the mechanism for the changes). On the next few Titan flybys, we just get more pictures of the Xanadu-Sickle hemisphere. In 2005, though, I think that high-resolution infrared pictures of the Lying H will become possible, then Dog and Ball in 2006 and Dragon's Head in 2007. The most dramatic change will be the maneuver known as the Titan 180 Transfer in late 2006 and early 2007, during which the orbit will mutate and flip around so that it points in a completely different direction; in the meantime Cassini should be capable of taking some exceedingly awesome pictures of Saturn from way above the ring plane.
And, of course, other things are going to be happening, even with regard to Titan. The Huygens probe gets released this Christmas and attempts to land on Titan (in the western Sickle region) on January 14. Also, Cassini doesn't need sunlight to map Titan with radar, though those radar pictures have been even harder to interpret than the infrared ones so far; so far, the only thing that's clear about Titan is that it is a very strange place. I'm looking forward to getting some radar pictures of areas that have already been mapped in the infrared so that it's possible to get context; we might see that soon.
There will also be multiple close approaches to several other moons; I'm particularly looking forward to Iapetus (where Clarke put the big monolith in the book of 2001), Enceladus, Dione, and Hyperion (the only known body in the solar system that rotates chaotically). (That Planetary Society Saturn extravaganza has the best synopses of Pioneer/Voyager/HST/Cassini Saturn exploration that I've ever seen, and it looks as if they're keeping all the moon pages up to date as new pictures come in.)
Meanwhile, the pictures of Saturn and its rings continue to be amazing.
