PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
Contact: Jane Platt
FOR IMMEDIATE RELEASEJune 5, 1997
GALILEO FINDS WET SPOTS, DRY SPOTS AND NEW VIEW OF JUPITER'S
Jupiter has both wet and dry regions, just as Earth has
tropics and deserts, according to new images and data from the
Galileo spacecraft released today. The data may explain why
Galileo's atmospheric probe found much less water than scientists
had anticipated when it dropped into the Jovian atmosphere in
"We had suspected that the probe landed in the Sahara Desert
of Jupiter," said Dr. Andrew Ingersoll, a professor at the
California Institute of Technology and member of the Galileo
science team. "But the new data show there is moisture in the
surrounding areas. Jupiter is not as dry overall as we thought."
The area where the probe entered was a clearing in the
clouds -- a dry spot through which deeper, warmer layers can be
seen. By studying various areas, including those resembling the
probe entry site, the Galileo orbiter has helped scientists
understand the probe results. In fact, the air around a dry spot
has 100 times more water than the dry spot itself, according to
Dr. Robert Carlson, of NASA's Jet Propulsion Laboratory,
principal investigator for the imaging spectrometer instrument
Such dry spots cover less than 1 percent of the Jovian
atmosphere, and they appear to be regions where the winds
converge and create a giant downdraft, according to Caltech
graduate student Ashwin Vasavada. In fact, the water content of
the giant, gaseous planet varies at least as much as the moisture
varies from place to place on Earth.
"Winds rise from the deep atmosphere and lose water and
ammonia," explained Dr. Glenn Orton, a Galileo interdisciplinary
scientist at JPL and co-investigator on the photopolarimeter-
radiometer instrument. "At the top, when they converge and drop
back down, nothing is left to condense back into clouds, and a
dry clearing is created. These dry spots may grow and diminish,
but they recur in the same places, possibly because of the
circulation patterns on Jupiter."
Ingersoll said the dry spots are found in a band in the
northern hemisphere at 5 to 7 degrees latitude. When the Galileo
probe was released near the tops of the clouds, it found dry air
underneath. But at other locations, the weather might be rather
In the months since the probe's descent, Galileo mission
scientists have debated whether the dry conditions it encountered
were due to the downdraft concept, or whether Jupiter's water had
somehow been concentrated deep in the gas planet's interior as it
formed and evolved four billion years ago. "There was a cosmo-
chemical explanation and a meteorological explanation, and our
latest analysis clearly favors the idea that the dry spots are a
consequence of weather-related activity," Ingersoll said.
"Fifty miles below the cloud tops, we could expect
thunderstorms, lightning and rain," Ingersoll added. "But in
contrast to Earth, individual Jovian storms and weather systems
sometimes last for months, years or even centuries. The Great Red
Spot, for example, has existed for at least the 300 years that
we've been aware of it."
Despite the relatively warm temperatures and the presence of
water on Jupiter, Ingersoll said it is "highly unlikely" that the
planet could sustain life in its thick, gaseous environment
without any solid surface. He expressed the opinion that any
Jovian life forms would have to hover, and "while we might
imagine an advanced life form that could adapt, pre-biotic
compounds would not survive in that environment and, therefore,
evolution could not take place there."
The latest data from Galileo also shed new light on the
auroras which glow in a narrow ring around the poles of Jupiter.
The auroras, essentially a light show stretching like a ribbon
around the planet, are created when charged particles collide
with atmospheric particles, causing them to light up. The new
images show the night-side aurora for the first time.
Dr. Scott Bolton of JPL, co-investigator for the Galileo
plasma and plasma wave instruments, said the latest findings show
"Jupiter's auroras are a lot like the auroras we see on Earth as
the northern lights. However, we now know that the auroral arc on
Jupiter is thin and patchy, and we can also estimate its altitude
is between 300 and 600 kilometers (185 to 370 miles)."
These auroras had previously been viewed in ultraviolet
light by the Hubble Space Telescope, and in infrared light by
Earth-based telescopes, but Galileo was able to capture images of
the auroras in visible light and from a closer vantage point.
Galileo was launched in 1989 and entered orbit around
Jupiter on Dec. 7, 1995. The Galileo mission is managed by JPL
for NASA's Office of Space Science, Washington, DC.
Images and other data received from Galileo are posted on
the Galileo home page on the World Wide Web at