I am mostly a biology person, and PT is mostly a biology blog, but I think we can all take a moment to have a gasp at the results of the first moon flyby of the Cassini-Huygens mission to Saturn.
Quite an improvement over the last few days, eh? Check the continually-updated latest images from Cassini page at JPL, where you can view the images at almost whatever resolution you desire. The Cassini team will probably be adding images rapidly from now on.
For the past several months, the Cassini-Huygens probe has been racing towards Saturn, after a seven-year journey that included four gravity-assist manuevers in the inner solar system to pick up speed. The Cassini website has been posting pictures about once a week, mostly of Saturn getting bigger…and bigger…and bigger in the zoom cameras. However, the first stop on the Deluxe Grand Tour of Saturn was Saturn’s largest outer moon, Phoebe. Cassini flew past Phoebe late last week and the images have been coming in this weekend.
The Cassini probe is the size of a bus, has a mass of 6000 kilograms*, and is packed with high-tech cameras and instruments far superior to those carried on the Voyager probes. It appears that all sensors worked perfectly on the Phoebe flyby, as well as the antenna that transmits the data back to Earth. This is very important – the big problem with the Galileo space probe to Jupiter was that its main antenna wouldn’t open, meaning that all data had to be trickled back through a low-bandwidth backup antenna. The Galileo probe still did an excellent job, but Cassini will be able to send us gigabytes of data a day.
Phoebe is interesting because it has a “retrograde” orbit around Saturn, meaning that it orbits in the opposite direction to Saturn’s inner moons (Saturn has a few outer moons smaller than Phoebe that also have retrograde orbits – they may be bits of Phoebe blasted off by impacts). Phoebe’s orbit is also in the plane of the solar system, rather than the plane of Saturn’s rings and inner moons. These facts, along with Phoebe’s dark surface, indicate that Phoebe may be a bit of the outer solar system that wandered in and was captured by Saturn’s gravity. Therefore, today’s images might be the first good look that we have ever gotten of a primitive, unprocessed piece of the outer solar system.
A few things that I find interesting about the photos thus far: Phoebe is clearly so small that it barely has enough gravity to keep a spherical shape, and impacts are able to blast large pieces off of it. I suspect that the steepness of the craters is also a result of the low gravity. It is also clear that some craters are fresher than others, and one fresh crater appears to reveal some layering of ice (brighter material) and darker material (perhaps organic compounds?).
But, this is only the first stop on the tour. Cassini is NASA’s last “Cadillac” probe, where billions of dollars were spent to pack everything onto one probe. After problems with previous Cadillac missions, NASA switched to a “faster, better, cheaper” philosophy. This may be appropriate for Mars missions, where the travel time is only 6 months, but for the outer planets, big probes with lots of sensors are really the only way to go. And finally, it appears that we have a deluxe probe that is functioning perfectly.
What we have to look forward to: 30 more (known) moons, 70-some orbits of Saturn over the next 4 years, and the December dropping of the Huygens probe into Titan’s mysterious organic-haze atmosphere. But the next big event is on July 1: a flight through Saturn’s rings (between the F- and G-rings) and an ultra-close approach to Saturn:
I think I know what I’ll be doing over the July 4 weekend.
* Mark Perakh pointed out that my original description, “weight of 6,000 kilograms” was only correct while Cassini was on the Earth’s surface. In space its weight is ~0. Its mass remains 6,000 kg. You can’t get away with anything here in the Thumb…