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JET PROPULSION LABORATORY
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Contact at JPL: Jane Platt 818-354-0880
Contact at Ames: Kathleen Burton 650-604-1731
FOR IMMEDIATE RELEASE
November 17, 1999
GALILEO PROBE RESULTS SUGGEST JUPITER HAD AN ANCIENT, CHILLY PAST
Jupiter's history may be much older and colder than
previously believed, according to newly released findings from
NASA's Galileo spacecraft published in the November 18 edition of
the journal Nature.
"This new information might shake up our view of how the
solar system formed," said Dr. Tobias Owen, astronomy professor
at the Institute for Astronomy of the University of Hawaii,
Honolulu, HI, and a scientist on the Galileo probe neutral mass
spectrometer instrument team. When Galileo arrived at Jupiter on
December 7, 1995 and dropped a probe into the atmosphere of the
huge, gaseous planet, the mass spectrometer measured the chemical
composition of Jupiter's atmosphere.
In Jupiter's atmosphere, the spectrometer detected
surprisingly high concentrations of argon, krypton and xenon,
three chemical elements called noble gases because they are very
independent and don't combine with other chemicals. Tiny traces
of these gases are found in the air we breathe on Earth, and
argon is sometimes used like neon in advertising signs.
The discovery of these gases in such high quantities at
Jupiter raises questions about how they got there. "In order to
catch these gases, Jupiter had to trap them physically by
condensation or freezing," Owen said. This process, he said,
requires extremely cold temperatures of about -240 degrees
Celsius (-400 degrees Fahrenheit), colder than the surface of
Pluto, the planet farthest from the Sun. Planetesimals (small
objects orbiting the Sun) in the Kuiper Belt beyond Pluto would
be this cold, but Jupiter is more than six times closer to the
Sun and thus is much warmer. For this reason, Jupiter could not
have been the site where the three noble gases were originally
"This raises some intriguing possibilities," Owen said.
"One explanation suggests that Jupiter was formed out in the area
around the Kuiper Belt and was dragged inward to its present
location. Another possibility is that the solar nebula, a huge
cloud of gas and dust from which our solar system formed, was
much colder than scientists believe. A third hypothesis proposes
that the solid materials that brought these noble gases to
Jupiter began forming in the original huge, interstellar cloud of
gas and dust even before it collapsed to form the solar nebula.
That would make these icy materials older and more primitive than
we had expected."
"If either of the last two hypotheses turns out to be
correct, it would suggest that giant planets can form closer to
their stars than current theories predict," Owen said. "This
could help explain the new observations of planetary systems
around other stars, in which such close-in giant planets are
"These new Galileo probe results provide new insights into
how planets form in the solar system and around other stars,"
said Galileo project scientist Dr. Torrence Johnson of NASA's Jet
Propulsion Laboratory, Pasadena, CA.
Measuring the composition of Jupiter's atmosphere was a
primary scientific objective of the probe, because we knew it
could change our understanding of Jupiter's formation and
evolution," said Galileo probe project scientist Dr. Richard
Young of NASA Ames Research Center, Moffett Field, CA. "These
latest probe results have done exactly that, and the measurements
are the sort that could only have been obtained by in-situ
measurements from an entry probe."
Owen's co-authors on the Nature article are: Drs. Paul
Mahaffy and Hasso Niemann of NASA's Goddard Space Flight Center,
Greenbelt, MD, Drs. Sushil Atreya and Thomas Donahue of the
University of Michigan, Ann Arbor, MI, Dr. Akiva Bar-Nun of the
University of Tel Aviv, Israel, and Dr. Imke de Pater of the
University of California, Berkeley. Although the data were
collected by the Galileo probe in December 1995, careful and
thorough analysis was necessary in Earth laboratories to verify
When it dropped 156 kilometers (97 miles) through Jupiter's
atmosphere, the Galileo probe relayed data back to the main
Galileo spacecraft more than 209,215 kilometers (130,000 miles)
overhead for storage and transmission to Earth. The probe
operated longer than expected during its descent deep into the
atmosphere, but was finally overcome by Jupiter's high
temperatures and pressures.
The Galileo spacecraft, meanwhile, has been orbiting Jupiter
and its moons for nearly four years, beaming back to Earth
thousands of pictures and a wealth of scientific data. Its two-
year, primary mission ended in December 1997, but it was followed
by the current, two-year extended mission.
Artist's concepts of the Galileo spacecraft and probe can be
accessed at http://www.jpl.nasa.gov/pictures/solar/gllartist.html
. Further information and images about the Galileo mission can
be accessed at http://galileo.jpl.nasa.gov .
The Galileo Project is managed by Jet Propulsion Laboratory
and the Galileo atmospheric probe is managed by Ames Research