Phoebe:
Posted on 06/10/2004 8:39:38 AM PDT by cogitator
While the Reagan Funeral is obviously important, Cassini-Huygens must keep its designated appointment in the heavens on the National Day of Mourning:
Cassini Spacecraft Near First Stop In Historic Saturn Tour
Saturn by Cassini and team Pasadena (JPL) Jun 10, 2004 The most complex interplanetary mission ever launched is about to meet one of the solar system's enigmatic moons. Cassini will fly by Saturn's largest outer moon, Phoebe, on Friday, June 11. The closest approach is at approximately 1:56 p.m. Pacific Time, just 19 days before Saturn arrival.
A final trajectory correction maneuver is scheduled for June 16. On arrival date, June 30, Cassini will become the first spacecraft to orbit Saturn. Once in orbit it will conduct an extensive, four-year tour of the Saturn system, including its majestic rings and many known moons.
"The arrival date and trajectory to Saturn were specifically selected to accommodate this flyby, which will be the only opportunity during the mission to study Phoebe at close range," said Dave Seal, mission planner for the Cassini-Huygens mission at NASA's Jet Propulsion Laboratory, Pasadena, Calif.
Phoebe at 4 million km out through to 2.5 million km out
"Phoebe's orbit is simply too far from Saturn, at almost 13 million kilometers (about 8 million miles), nearly four times as far as the next closest major satellite, Iapetus. A later encounter is not feasible."
"The last time we had observations of Phoebe was by Voyager in 1981," said Dr. Torrence Johnson, former Voyager imaging team member, Galileo project scientist and current Cassini imaging team member. "This time around, the pictures of the mysterious moon will be about 1,000 times better, as Cassini will be closer."
Voyager 2 captured images of Phoebe from about 2.2 million kilometers (about 1.4 million miles) away. Cassini will obtain images from a mere 2,000 kilometers (about 1,240 miles) above the moon's surface.
Cassini will also collect spectroscopic and radar data that could decipher the composition and origin of this distant moon. Cassini's Phoebe images, already twice as good as any image returned by Voyager 2, show large craters and variation in surface brightness.
"We anticipate that Phoebe will be heavily cratered in the higher resolution images we expect to see in the next few days," said Dr. Peter Thomas, a member of the imaging team and a senior research associate at Cornell University, Ithaca, N.Y., who specializes in studies of small satellites.
"The hints of different brightnesses also suggest that the highest resolution images, several hundred times better, will show a variety of materials.
Discovered in 1898 by American astronomer William Henry Pickering, Phoebe is of great interest to scientists.
"With the instruments Cassini carries, we might learn more about Phoebe's internal structure and composition. What we have are many unanswered questions: Did it ever melt? Does it have evidence of past interior melting? Was it ever an icy body? Why is Phoebe in such an odd orbit?" Said Dr. Dennis Matson, project scientist for the Cassini-Huygens mission at JPL.
Phoebe has a diameter of 220 kilometers (about 136.7 miles), which is equal to about one-fifteenth the diameter of Earth's moon. Phoebe rotates on its axis every nine hours and 16 minutes, and it completes a full orbit around Saturn in about 18 months. Its elliptical orbit is inclined approximately 30 degrees to Saturn's equator.
Phoebe's retrograde orbit means that it goes around Saturn in the opposite direction of the larger interior Saturnian moons. Previous ground-based observations have shown water ice present on its surface.
Phoebe is also unusual in that it is very dark. It reflects only six percent of the sunlight it receives. Phoebe's darkness and retrograde orbit suggest that it is most likely a captured object. A captured object is a celestial body that is caught by the gravitational pull of a much bigger body, generally a planet.
Some scientists believe Phoebe might even be an object from the outer solar system, similar to the objects found in the Kuiper Belt. The Kuiper Belt is a collection of small icy bodies beyond Pluto that were never drawn together by gravity to form a planet.
"The dark and odd-shaped Phoebe may be a piece of the building blocks from which some of the planets formed," said Dr. Bonnie Buratti, scientist on the Cassini-Huygens mission at JPL. "It might hold clues about the early formation of our solar system."
Saturnian ping
Science list ping (a subset of the evolution list). FReepmail me to be added or dropped.
What, no one's posted any Lisa Kudrow images yet? It's getting too serious around here. ;-)
Looks a bit like a celestial golf ball.
This is getting pretty exciting! :-)
Titan is bloody huge. It would be a planet if it were circling a star instead of a planet.
You said it! :-)
It's going to mighty crowded around Saturn. Exclusive of Saturn's rings, there are 30 natural satellites orbiting that planet. I hope someone remembered to call ahead for reservations!
--Boot Hill
I can't wait to get a close up look at those moons. And the landing on Titan is going to be outta this world -- literally! :-)
I think the interesting stuff is still happening on Mars. There are people who say the pictures show obvious evidence of trilobites and stromatolites. One of the early pics I saw from the Spirit rover showed a trilobite as plain as day, like I was holding it in my hand.
Looks even more like one of these:
Eight hours to go to flyby!
Could some pictures be ready for the evening news?
Hey RA! Did you have any input on Cassini? This is very exciting.
I agree, but I'd really like a better look at Iapetus. Particularly to see if the Stargate is still there (reference to the original "2001: A Space Odyssey" novel by Arthur C. Clarke).
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.