From: LARRY KLAES (ljk4_at_msn.com)
Date: Thu Jul 01 2004 - 13:57:02 PDT
----- Original Message -----
From: NASA Jet Propulsion Laboratory<mailto:info_at_jpl.nasa.gov>
To: ljk4_at_msn.com<mailto:ljk4_at_msn.com>
Sent: Monday, June 28, 2004 7:18 PM
Subject: Scientists Find That Saturn's Rotation Period Is A Puzzle
MEDIA RELATIONS OFFICE
Carolina Martinez (818) 354-9382
Gary Galluzzo (319) 384-0009
News Release: 2004-164 June 28, 2004
Scientists Find That Saturn's Rotation Period Is A Puzzle
On approach to Saturn, data obtained by the Cassini spacecraft are
Cassini took readings of the day-length indicator regarded as most
Cassini scientists are not questioning Voyager's careful measurements.
The radio sounds of Saturn's rotation, which are also the first sounds
"The rotational modulation of radio emissions from distant
The first hint of something strange about that type of measurement at
Dr. Michael D. Desch, Cassini Radio Plasma Wave Science team member,
Gurnett said, "Although Saturn's radio rotation period has clearly
"This finding is very significant. It demonstrates that the idea of a
"I think we will be able to unravel the puzzle, but it's going to take
Cassini, carrying 12 scientific instruments, is just two days from its
The Cassini-Huygens mission is a cooperative project of NASA, the
-end-
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: Thu Jul 01 2004 - 14:07:06 PDT
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov
Jet Propulsion Laboratory, Pasadena, Calif.
University of Iowa, Iowa City
already posing a puzzling question: How long is the day on Saturn?
reliable, the rhythm of natural radio signals from the planet. The
results give 10 hours, 45 minutes, 45 seconds (plus or minus 36
seconds) as the length of time it takes Saturn to complete each
rotation. Here's the puzzle: That is about 6 minutes, or one percent,
longer than the radio rotational period measured by the Voyager 1 and
Voyager 2 spacecraft, which flew by Saturn in 1980 and 1981.
And they definitely do not think the whole planet of Saturn is
actually rotating that much slower than it did two decades ago.
Instead, they are looking for an explanation based on some variability
in how the rotation deep inside Saturn drives the radio pulse.
from Saturn studied by Cassini, are like a heartbeat and can be heard
by visiting http://www.jpl.nasa.gov/videos/cassini/0604/
http://www-pw.physics.uiowa.edu/space-audio
astronomical objects has long been used to provide very accurate
measurements of their rotation period," said Dr. Don Gurnett,
principal investigator for the Cassini Radio and Plasma Wave Science
instrument, University of Iowa, Iowa City. "The technique is
particularly useful for the giant gas planets, such as Jupiter and
Saturn, which have no surfaces and are covered by clouds that make
direct visual measurements impossible."
Saturn was in 1997, when a researcher from Observatoire de Paris
reported that Saturn's radio rotation period differed substantially
from Voyager.
and scientist at NASA's Goddard Space Flight Center in Greenbelt, Md.,
has analyzed Saturn radio data collected by Cassini from April 29,
2003, to June 10, 2004. "We all agree that the radio rotation period
of Saturn is longer today than it was in during the Voyager flyby in
1980," he said.
shifted substantially since the Voyager measurements, I don't think
any of us could conceive of any process that would cause the rotation
of the entire planet to actually slow down. So it appears that there
is some kind of slippage between the deep interior of the planet and
the magnetic field, which controls the charged particles responsible
for the radio emission." He suggests the solution may be tied to the
fact that Saturn's rotational axis is nearly identical to its magnetic
axis. Jupiter, with a more substantial difference between its
magnetic axis and its rotational axis, shows no comparable
irregularities in its radio rotation period.
rigidly rotating magnetic field is wrong," said Dr. Alex Dessler, a
senior research scientist at the University of Arizona, Tucson. In
that way, the magnetic fields of gas giant planets may resemble that
of the Sun. The Sun's magnetic field does not rotate uniformly.
Instead, its rotation period varies with latitude. "Saturn's magnetic
field has more in common with the Sun than the Earth. The measurement
can be interpreted as showing that the part of Saturn's magnetic field
that controls the radio emissions has moved to a higher latitude
during the last two decades," said Dressler.
some time," said Gurnett. "With Cassini in orbit around Saturn for
four years or more, we will be in an excellent position to monitor
long-term variations in the radio period, as well as investigate the
rotational period using other techniques."
planetary rendezvous with Saturn. On June 30 it will become the first
spacecraft to orbit Saturn, when it begins a four-year study of the
planet, its rings and its 31 known moons. The spacecraft recently flew
past Saturn's cratered moon Phoebe, where it captured spectacular
images as well as data on its mass and composition.
European Space Agency and the Italian Space Agency. The Jet Propulsion
Laboratory, a division of the California Institute of Technology in
Pasadena, manages the Cassini-Huygens mission for NASA's Office of
Space Science, Washington, D.C. JPL designed, developed and assembled
the Cassini orbiter.
For the latest images and more information about the Cassini-Huygens
mission, visit http://www.nasa.gov/cassini