Combining all these observations gives positive identification of the presence of the ring from 128 to 207 Rs, though its extent could be larger. And there was no evidence for it in an observation centered at 400 Rs. Its presence was equivocal in an observation centered on Phoebe at 220 Rs. It was also seen in smaller snapshots that were centered on the outer moons Kiviuq (153 Rs) and Tarvos (180 Rs). What they found was "a diffuse double-peaked band of light coincident with Saturn's ecliptic plane." The band of light was found in an observation that spanned the region from 128 to 180 Rs. In February of this year, Verbiscer and her colleagues pointed Spitzer's Multiband Imaging Photometer (MIPS) to image the region in several disconnected locations along Saturn's ecliptic plane all the way from Iapetus' orbit to 400 Rs at wavelengths of 24 and 70 microns. It's so sparse that Cassini's instruments, wonderful though they are, have no hope of seeing the ring as any kind of object against black space.īut the Spitzer Space Telescope is a different story. But Phoebe's orbit is so incredibly large that this "ring" would be almost unimaginably sparse. Verbiscer and her coauthors predicted that there might be such a ring. So it is no stretch at all to imagine that, much as there is material in Aegaeon's orbit making the G ring, there should be material in Phoebe's orbit making a ring. It was so far from Saturn that after sailing past Phoebe it took Cassini 19 more days to get to its rendezvous with Saturn for its orbit insertion!!Īll it takes is one glance at Phoebe to know that a lot of it has been blasted away due to numerous impacts with other, smaller bodies. The Cassini mission made special plans to fly past Phoebe during its cruise to Saturn the encounter was on June 11, 2004. Standing out among these because of its size is Phoebe, which is 215 kilometers across, the only one that has ever been seen up close by a spacecraft. Their odd orbits have made astronomers suspect that they didn't form with Saturn but instead are captured wandering bodies - Centaurs or even Kuiper belt objects. These moons tend to be very, very small, only a handful of kilometers in diameter, and they have inclined, eccentric orbits that are anywhere from roughly 200 to 400 Rs - the triple-digit-Rs family. This is the double-digit-Rs family.īeyond Iapetus, there's another big gap and then you get to another totally different family. Next comes two-faced Iapetus, which - unlike all the moons I've listed so far - has a notably inclined orbit and is all the way out at almost 60 Rs. You have cloudy Titan and dark Hyperion at about 20 and about 24 Rs. These moons all look pretty similar.īeyond Rhea, the moons are suddenly spaced much farther apart, and have very different appearances. In terms of their distance from Saturn, you can think of them as the "single-digit-Rs" family. Most of Saturn's moons are part and parcel of the main ring system - the E ring includes the orbits of Mimas, Enceladus, Tethys, Dione, and possibly Rhea. So when I say that the new ring discovered by Anne Verbiscer and her coworkers extends from 128 to 207 Rs, you should really be pretty amazed. The main ring system, the part that's almost perfectly flat and aligned with Saturn's equator, includes the D, C, B, A, and F rings and is just a bit more than twice Saturn's diameter.Į ring: 9 Rs.
Beginning at Saturn's center, one radius gets you to Saturn's cloud tops. One Saturn radius, abbreviated as R-subscript-s but usually written just as Rs to make things easier, is 60,330 kilometers. ( Click here to skip the background and go straight to the Spitzer results.) You can measure the extent of the rings in kilometers, but astronomers and Cassini mission people both seem to find "Saturn radii" to be a handier unit that helps them have a better intuitive feel for the scale of things. Sorry I'm late to this news, but as usual I'll try to compensate by being thorough! Last week, planetary astronomers Anne Verbiscer, Michael Skrutskie, and Doug Hamilton published a paper in Nature succinctly titled " Saturn's Largest Ring." In the paper, they announce the discovery, using the Spitzer infrared space telescope, of a gargantuan, previously unseen ring around Saturn, encompassing the orbit of Phoebe.įirst, let's start with some background on the scale of Saturn's known rings.
0 kommentar(er)
