Jupiter's Atmosphere

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 of satisfaction.

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 atmosphere.

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 Jupiter's coulds

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 Spot Goes."

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 bottom.

Below are two press releases from the Galileo team that give more detail about Jupiter's clouds.

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

Douglas Isbell
Headquarters, Washington, DC January 22, 1996
(Phone: 202/358-1547)

David Morse
Ames Research Center, Mountain View, CA
(Phone: 415/604-4724)

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," he noted.

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 evolution.

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 operations.

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 storms."

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 hydrogen composition.

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:
http://ccf.arc.nasa.gov/dx
http://ccf.arc.nasa.gov/galileo_probe/
http://www.jpl.nasa.gov/galileo

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


Douglas Isbell
Headquarters, Washington, DC March 18, 1996
(Phone: 202/358-1753)

Ann Hutchison
Ames Research Center, Mountain View, CA
(Phone: 415/604-4968)

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 View, CA.

"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 extremely remote.

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 Sun.

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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