- Original Message -
From: NASA Jet Propulsion Laboratory
Sent: Thursday, December 30, 2004 8:48 PM
Subject: Cassini Caps off 2004 With Flyby of Icy Moon
Iapetus
Carolina
Martinez (818) 354-9382
Jet
Propulsion Laboratory, Pasadena, Calif.
News
Release: 2004-300
December 30, 2004
Cassini
Caps off 2004 With Flyby of Icy Moon Iapetus
NASA's
Cassini spacecraft is set to cap off 2004 with an encounter of Saturn's
ying-yang moon Iapetus (eye-APP-eh-tuss) on New Year's Eve.
This
is Cassini's closest pass yet by one of Saturns smaller icy satellites
since its arrival around the ringed giant on June 30 of this year. The next close flyby of
Iapetus is not until 2007.
Iapetus
is a world of sharp contrasts. The leading hemisphere is as dark
as a freshly-tarred street, and the white, trailing hemisphere resembles
freshly-fallen snow.
Cassini
will fly by the two-toned moon at a distance of approximately 123,400
kilometers (76,700 miles) on Friday, Dec. 31. This flyby brings to an end
a year of major accomplishments and rings in what promises to be a year
filled with new discoveries about Saturn and its moons.
"I can think of
no better way than this to wrap up what has been a whirlwind year," said
Robert T. Mitchell, program manager for the Cassini mission at NASA's Jet
Propulsion Laboratory, Pasadena, Calif. "The new year offers new
opportunities, and 2005 will be the year of the icy satellites."
In 2005 Cassini
will have 13 targeted encounters with five of Saturn's moons. "We have 43 close flybys of Titan
still ahead of us during the four-year tour. Next year, eight of our 13 close
flybys will be of Titan. We
will also have a number of more distant flybys of the icy satellites, and
let's not forget Saturn and the rings each time we come around," said
Mitchell.
With a diameter of about 1,400 kilometers (890 miles), Iapetus is
Saturn's third largest moon.
It was discovered by Jean-Dominique Cassini in 1672. It was Cassini, for whom the
Cassini-Huygens mission is named, who correctly deduced that one side of
Iapetus was dark, while the other was white.
Scientists
still do not agree on whether the dark material originated from an outside
source or was created from Iapetus' own interior. One scenario for the
outside deposit of material would involve dark particles being ejected
from Saturns little moon Phoebe and drifting inward to coat Iapetus. The major problem with this model
is that the dark material on Iapetus is redder than Phoebe, although the
material could have undergone chemical changes that made it redder after
its expulsion from Phoebe. One observation lending credence to the theory
of an internal origin is the concentration of material on crater floors,
which implies that something is filling in the craters. In one model
proposed by scientists, methane could erupt from the interior and then
become darkened by ultraviolet radiation.
Iapetus is odd in other respects. It is the only large Saturn moon in a
highly inclined orbit, one that takes it far above and below the plane in
which the rings and most of the moons orbit. It is less dense than objects
of similar brightness, which implies it has a higher fraction of ice or
possibly methane or ammonia in its interior.
The last look at Iapetus was by NASA's Voyager 1 and 2 spacecraft in
1980 and 1981. The Cassini
images will be the highest resolution images yet of this mysterious
moon.
The Iapetus flyby by Cassini follows the
successful release of the Huygens probe on December 24.
More
information on the Cassini-Huygens mission is available at:http://saturn.jpl.nasa.gov andhttp://www.nasa.gov/cassini.
The
Cassini-Huygens mission is a cooperative project of NASA, the European
Space Agency and the Italian Space Agency. JPL, a division of the California
Institute of Technology in Pasadena, manages the Cassini mission for
NASA's Science Mission Directorate, Washington, D.C. JPL designed, developed and
assembled the Cassini orbiter. The European Space Agency built
and managed the development of the Huygens probe and is in charge of the
probe operations. The Italian
Space Agency provided the high-gain antenna, much of the radio system and
elements of several of Cassini's science instruments.
Cassini
spacecraft targeted satellite encounters for 2005:
Titan:
January 14, 2005
Titan:
February 15, 2005
