This image, taken by the Galileo spacecraft, serves once again to demonstrate
just how beautiful Jupiter it, as well as how complicated its weather bands
are. The information underneath the photograph will attempt to fill in gaps
in your understanding of the atmosphere of Jupiter, although far more questions
will still remain unanswered.
Jupiter's "atmosphere" is kind of a misleading choice of words since
the planet is composed of gas. What we are referring to here is the part of
that gas planet that we visualize and know something about. As you can see from
this spectacular image from the Galileo spacecraft, the atmosphere of Jupiter
is very complex. When the Voyager first began returning pictures from Jupiter
back in 1979, astronomers were stunned by all of the activity they saw in time-lapse
photography. Storms would pop up, get ripped apart, and then reform ... all
in a day or two. To see any kind of order amidst such apparent chaotic motion
was indeed startling. And, while storms were coming and going, one great storm,
The Great Red Spot, has remained for over 350 years. Why is this storm running
unabated for so long while all other storms die out quickly. Another question
astronomers had to answer was why does Jupiter have complex color bands. Since
the Voyager missions, and now the current Galileo missions, many questions regarding
Jupiter's clouds have been answered, if not completely, at least to some degree
Jupiter holds clues to many of the mysteries of the early solar system. About
4.5 billion years ago, when the solar system formed out of a swirling mass of
gases and dust called the solar nebula, Jupiter's core probably began as a solid
mass of ice and rock about 15 times the bulk of Earth. The ice content of Jupiter's
mass was high because it formed in the colder outer region of the solar system,
where the nebula contained a lot of ice particles, principally water and methane.
Probably because icy masses can adhere and compress into a single large body
faster than plain rock can, the outer planets formed their cores before the
rocky inner planets did. The gravity of the large icy cores of Jupiter and Saturn
attracted most of the light hydrogen and helium gas in the nebula, and it is
these gasses that we find dominating their atmospheres today. Jupiter, the innermost
of the icy giants, "grew" the largest atmosphere. In fact, the face
of Jupiter that we see is really just the top of its atmosphere. What goes on
inside is even more intriguing.
Jupiter's massive atmosphere creates tremendous pressures as you move closer
to the center of the planet. The substances inside the atmosphere are subject
to extreme conditions, leading to exotic chemistry. For example, scientists
have reason to believe that the inner layers of hydrogen in Jupiter's atmosphere,
under the pressure of the atmosphere above, may have formed into a planet-encircling
layer of what is called liquid metallic hydrogen. Not exactly an ocean, not
exactly atmosphere, this layer of hydrogen would have properties that stretch
our understanding of chemistry. Instead of the simple, free-moving and loosely
bonded behavior of gaseous hydrogen, liquid metallic hydrogen is a strange matrix
capable of conducting huge electrical currents. The persistent radio noise and
improbably strong magnetic field of Jupiter could both emanate from this layer
of metallic liquid. Some scientists theorize that beneath this layer there is
no solid mass at the center of Jupiter, but that the unique temperature and
pressure conditions sustain a core whose density is more like liquid or slush.
Farther from the planet's core, in what we can more certainly call the atmosphere,
we see gases behaving in a more familiar manner, moving in general planetary
circulations driven primarily by the rotation of the planet. Jupiter is believed
to have three cloud layers in its atmosphere. At the top are clouds of ammonia
ice; beneath that ammonium-hydrogen sulfide crystals; and in the lowest layer,
water ice and perhaps liquid water. Jupiter is noteworthy for its turbulent
cloudtops, and its long-standing storm, the Great Red Spot. The origins of these
colorful features are uncertain, but scientists believe that they are caused
by plumes of warmer gases that rise up from deep in the planet's interior. The
plumes' colors are probably caused by their chemical content. Although the amount
of carbon, for example, in the Jovian atmosphere is very small, carbon readily
combines with hydrogen and trace amounts of oxygen to form a variety of gases
such as carbon monoxide, methane, and other organic compounds. The orange and
brown colors in Jupiter's clouds may be attributable to the presence of organic
compounds, or sulfur and phosphorus.
The past three paragraphs were taken directly from the Galileo
mission site that reveals some of the mission's discovery regarding Jupiter's
I have placed some of my favorite images of Jupiter's clouds below, just for
your viewing pleasure. I remind you, as I need to do so for myself, that these
are actual photographs and not paintings. I would think even the most skilled
impressionistic painter would have a difficult time duplicating the beauty of
I tossed these images, seen below, just to remind you that other spots on
Jupiter deserve recognitition. Left is a color-enhanced image of the clouds
near the Great Red Spot. In the middle is the Great White Spot, trying hard
to gain the noteriety of its neighbor, but alas ... the Great White Spot was
ripped apart by all of the winds of Jupiter's bands, as too was the Great Brown
Spot seen below right. I think that there might be a good children's book that
could combine the images of Jupiter with basic reading skills for a kindergartener:
"See the Red Spot ... See the White Spot ... See the Brown Spot ... The
Red Spot is Big ... The Brown Spot is Small ... The Red Spot Stays ... The White
Here are two images of the Great Red Spot. The lower left is in natural color
from the Galileo probe, while the lower right is a color-enhanced version from
the Voyager mission.
Below is a series of images taken by the Hubble Space Telescope showing the
changes in the Great Red Spot over a period of time form 1992 to 1999, top to
Below are two press releases from the Galileo team that give more detail about
Galileo Probe Science Results
Galileo Scientists Report Changing Findings About Jupiter - March 18, 1996
Probe Press Conference Graphics and Probe Animation Stills
Summary of First Science Results from the Galileo Probe
Headquarters, Washington, DC January 22, 1996
Ames Research Center, Mountain View, CA
RELEASE: January, 1996 - (96-10)
GALILEO PROBE SUGGESTS PLANETARY SCIENCE REAPPRAISAL
Preliminary analysis of early data returned by NASA's historic Galileo probe
mission into Jupiter's atmosphere has provided a series of startling discoveries
for project scientists.
Information on the extent of water and clouds and on the chemical composition
of the Jovian atmosphere is particularly revealing. Probe instruments found
the entry region of Jupiter to be drier than anticipated, and they did not detect
the three-tiered cloud structure that most researchers had postulated. The amount
of helium measured was about one-half of what was expected.
These initial findings are encouraging scientists to rethink their theories
of Jupiter's formation and the nature of planetary evolution processes, according
to probe project scientist Dr. Richard Young of NASA's Ames Research Center,
Mountain View, CA.
"The quality of the Galileo probe data exceeds all of our most optimistic
predictions," said Dr. Wesley Huntress, NASA Associate Administrator for
Space Science. "It will allow the scientific community to develop valuable
new insights into the formation and evolution of our solar system, and the origins
of life within it."
The probe made the most difficult planetary atmospheric entry ever attempted,
according to probe manager Marcie Smith of NASA Ames. Entering Jupiter's atmosphere
on Dec. 7, 1995, it survived entry speeds of over 106,000 mph, temperatures
twice those on the surface of the Sun and deceleration forces up to 230 times
the strength of gravity on Earth. It relayed data obtained during its 57-minute
descent mission back to the Galileo orbiter more than 130,000 miles overhead
for storage and transmission to Earth. The orbiter is now embarking on a two-year
mission to study Jupiter and its moons.
"The probe detected extremely strong winds and very intense turbulence
during its descent through Jupiter's thick atmosphere. This provides evidence
that the energy source driving much of Jupiter's distinctive circulation phenomena
is probably heat escaping from the deep interior of the planet," Young
said. "The probe also discovered an intense new radiation belt approximately
31,000 miles above Jupiter's cloud tops, and a veritable absence of lightning,"
The composition of Jupiter's atmosphere offered some surprises, according
to project scientists. It contains significantly lower than expected levels
of helium, neon, and certain heavy elements, such as carbon, oxygen and sulfur.
The issue of the colors of Jupiter's atmosphere has been much-debated, but
no consensus has developed from probe data to date. The probe encountered no
solid objects or surfaces during its entire 373-mile (600 km) journey. This
was as expected for a gas-giant planet such as Jupiter.
What are the implications of these findings? Most scientists believe that
Jupiter has a bulk composition similar to that of the gas and dust cloud of
the primitive solar nebula from which the planets and our Sun were formed, with
added heavy elements from comets and meteorites. The probe's measurements may
necessitate a re-evaluation of existing views of how Jupiter evolved from the
solar nebula. For example, the lower-than-expected helium and neon levels on
Jupiter relative to the Sun influence scientific understanding of the process
of fractionation, the "raining out" of helium and neon during planetary
During the probe's high-speed, atmospheric-entry phase, deceleration measurements
high in the atmosphere showed atmospheric density to be much greater than expected.
Corresponding temperatures were also much higher than predicted. The high temperatures
appear to require an unidentified heating mechanism for this region of the atmosphere.
Following probe parachute deployment, six science instruments on the probe
collected data throughout 97 miles (156 km) of the descent. During that time,
the probe endured severe winds, periods of intense cold and heat and strong
turbulence. The extreme temperatures and pressures of the Jovian environment
eventually caused the probe communications subsystem to terminate data transmission
Earth-based telescopic observations suggest that the probe entry site may
well have been one of the least cloudy areas on Jupiter. At this location, the
probe did not detect the three distinct layers of clouds (a topmost layer of
ammonia crystals, a middle layer of ammonium hydrosulfide, and a final, thick
layer of water and ice crystals) that researchers had anticipated.
Some indication of a high-level ammonia ice cloud was detected by the net
flux radiometer. Evidence for a thin cloud which might be the postulated ammonium
hydrosulfide cloud was provided by the nephelometer experiment. There was no
data to suggest the presence of water clouds of any significance. The vertical
temperature gradient obtained by the atmospheric structure instrument was characteristic
of a dry atmosphere, free of condensation. Only the one, distinctive cloud structure
was identified, and that was of modest proportion.
The latest analyses of data from the Voyager spacecraft that flew by Jupiter
in 1979 have suggested a water abundance for the planet of twice the solar level
(based on the Sun's oxygen content). Observations of the propagation of atmospheric
waves across Jupiter's cloud tops from the Comet Shoemaker-Levy 9 impacts implied
that Jupiter might have a water content of ten times the solar level. Actual
probe measurements, while subject to scientific debate, suggest a level near
that of the Sun. Scientists are left to wonder, "where is the oxygen?,"
"where is the water?," and to reconsider their interpretation of the
S-L 9 impacts.
Scientists had expected to find severe winds on Jupiter ranging up to 220
mph. However, the probe appears to have detected winds far greater, perhaps
up to 330 mph. The winds remained fairly constant as the probe descended deep
into the Jovian atmosphere. This suggests that Jupiter's winds are not caused
by differential sunlight at the equator versus the poles or by heat released
by water condensation as on Earth, according to project scientists.
"The origin of Jupiter's winds appears to be the internal heat source
which radiates energy up into the atmosphere from the planet's deep interior,"
Young said. "This impacts Jupiter's climate and circulation patterns, and
suggests a jet stream-like mechanism rather than swirling hurricane or tornado-like
The probe found that lightning occurs on Jupiter only about one-tenth as often
as on Earth. This is puzzling, but consistent with the absence of water clouds.
A virtual absence of lightning reduces the probability of finding complex organic
molecules in Jupiter's atmosphere, particularly given its hostile, predominantly
Scientists caution that results obtained to date, while dramatic and exciting,
are only preliminary and subject to much further analysis and refinement. Data
transmission problems associated with solar conjunction between the Earth and
Jupiter, the need to refine estimates based on probe and orbiter trajectories,
the presence of higher than anticipated instrument temperatures, and the need
for improved calibration all require a cautious approach to these early findings.
Additional information will be forthcoming over the next few months as scientists
continue to evaluate the wealth of data obtained by the probe and to cross-compare
results of individual scientific instruments. Further information and images
about the Galileo mission to Jupiter can be accessed on the Internet through
the following three URLs:
The Galileo probe project is managed by NASA's Ames Research Center, Mountain
View, CA. Hughes Aircraft Co., El Segundo, CA, designed and built the probe;
General Electric, Philadelphia, PA, built the probe's heat shield. NASA's Jet
Propulsion Laboratory, Pasadena, CA, built the Galileo orbiter spacecraft and
manages the overall mission.
Galileo Scientists Report Changing Findings About Jupiter
Headquarters, Washington, DC March 18, 1996
Ames Research Center, Mountain View, CA
RELEASE: March, 1996 - (96-54)
GALILEO SCIENTISTS REPORT CHANGING FINDINGS ABOUT JUPITER
Scientists continuing to analyze information returned by the Galileo atmospheric
probe that plunged into Jupiter last December report more surprises about the
giant gas planet.
Most significantly, the ratio of the elements that make up 99 percent of the
Jovian atmosphere -- helium and hydrogen -- now closely matches that found in
the Sun, suggesting that Jupiter's bulk composition has not changed since the
planet formed several billion years ago. Estimated amounts of key heavy elements
such as carbon and sulfur have increased, but minimal organic compounds were
detected, and estimates for Jupiter's wind speeds have climbed still higher.
Probe scientists are reporting these refined results today at the Lunar and
Planetary Science Conference in Houston, TX.
The ratio of helium to hydrogen by mass is key to developing theories of planetary
evolution. In the Sun, this value is about 25 percent. During a January 1996
press conference, Galileo probe scientists estimated that this number for Jupiter
was 14 percent. More comprehensive analysis of results from the probe's helium
abundance detector has raised this estimate for Jupiter to 24 percent.
"This increase implies that the amount of helium in the Jovian atmosphere
is close to the original amount that Jupiter gathered as it formed from the
primitive solar nebula that spawned the planets," according to Galileo
probe project scientist Dr. Richard Young of NASA's Ames Research Center, Mountain
"The revised helium abundance also indicates that gravitational settling
of helium toward the interior of Jupiter has not occurred nearly as fast as
it apparently has on Saturn, where the approximate helium-to-hydrogen ratio
is just six percent," said Young.
"This then confirms that Jupiter is much hotter in its interior than
its neighbor Saturn, the next largest planet in the Solar System. It also may
force scientists to revise their projections for the size of the rocky core
believed to exist deep in the center of Jupiter," he said.
The new estimate of the helium-to-hydrogen ratio on Jupiter is supported by
analysis of complementary data from the Galileo probe's neutral mass spectrometer.
These new helium results are raising related estimates for the abundances
of other key compounds, such as methane. Several heavy elements, including carbon,
nitrogen and sulfur, are significantly greater in abundance on Jupiter than
in the Sun. "This implies that the influx of meteorites and other small
bodies into Jupiter over the eons since its formation has played an important
role in how Jupiter has evolved," said Young.
However, minimal organic compounds were detected, indicating that such complex
combinations of carbon and hydrogen are rare on Jupiter and that the chances
of finding biological activity on Jupiter similar to that found on Earth are
The strong Jovian atmospheric winds continue to exceed expectations. Wind
speed estimates announced in January of up to 330 mph have grown to more than
400 mph. The winds persisted far below the one cloud layer detected, strongly
suggesting that heat escaping from deep in the planet's interior drives the
winds, rather than solar heating. Since all the outer giant planets exhibit
strong winds, scientists hope that understanding Jupiter's winds will lead to
important new insights into their unusual meteorology, Young said.
The scientists continue to report that the probe apparently entered Jupiter's
atmosphere near the southern edge of a so- called infrared hot spot, which is
believed to be a region of reduced clouds. "The probe's nephelometer observed
only one distinct cloud layer, and it is tenuous by Earth standards. It is likely
to be an ammonium hydrosulfide cloud," said Young. Three distinct cloud
layers (an upper layer of ammonia crystals, a middle layer of ammonium hydrosulfide,
and a thick bottom layer of water and ice crystals) were expected.
Further analysis of probe data has confirmed the preliminary report that the
Jovian atmosphere appears to be relatively dry, with much less water than anticipated
on the basis of solar composition and predictions from data sent by the Voyager
spacecraft that flew by Jupiter in 1979. These studies predicted a water abundance
for the planet of twice the solar level (based on the Sun's oxygen content.)
Actual probe measurements now suggest an amount of water less than that of the
Scientists confirmed that the probe's instruments found much less lightning
activity on Jupiter per unit area than on Earth. Lightning on Jupiter was found
to be about 1/10th of that found on Earth in an area of the same size. "Although
we found much less lightning activity, the individual lightning events are about
ten times more energetic than similar events on Earth," Young said.
"This is the sort of unique and exciting information that could not have
been obtained in any way other than an atmospheric entry probe," Young
said. Complete detailed results of the Galileo probe data analysis will be reported
in the May 10 issue of Science magazine.
The cone-shaped Galileo probe entered the atmosphere of Jupiter on Dec. 7,
1995, at a speed of over 106,000 mph and survived deceleration forces of 228
times Earth's gravity. After deploying a parachute, it relayed data to the Galileo
orbiter spacecraft overhead for 57 minutes.
The Galileo orbiter is beginning a two-year, 11-orbit tour of Jupiter and
will have its first major encounter with a Jovian moon on June 27 when it flies
closely by Ganymede. The orbiter successfully conducted a key engine burn on
March 14 to prepare for this encounter.
The Galileo probe project is managed by Ames. Hughes Space and Communications
Co., El Segundo, CA, designed and built the probe. Lockheed Martin Hypersonic
Systems (formerly General Electric), Philadelphia, built the probe's heat shield.
NASA's Jet Propulsion Laboratory, Pasadena, CA, built the Galileo orbiter spacecraft
and manages the overall mission.
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