Category: Jupiter

Jupiter’s moon Io is peppered with volcanoes, the hottest, most active volcanoes in our solar system. Sizzling vents spew plumes of gas and dust as much as 400 km high. They surge, spit, subside and surge again, non-stop.

The towering plumes, outlined by graceful arcs of rising and falling ash, are eerily beautiful. Their tops jut into space, freezing. Beneath them, scientists believe, it snows. Sulfurous flakes crystallize in the plume-tops and drift gently down to coat Io’s colorful terrain.

High above the falling snow something unexpected happens: At the apex of the plumes, some of the ash and dust that ought to turn around and fall … doesn’t. Defying gravity, it keeps going up, not slowing but accelerating, 2 times, 10 times, hundreds of times faster than a speeding bullet, away from Io and into deep space.

Passing spacecraft beware: Io is shooting at you.

The Ulysses spacecraft, a joint mission of NASA and the European Space Agency, made the discovery in 1992 when, approaching Jupiter, it was hit by a breakneck stream of volcano dust.

“What a surprise,” recalls Harold Krueger of the Max Planck Institute in Heidelberg, the principle investigator for Ulysses’ dust detector. “We expected to encounter dust,” he says. The solar system is littered with flakes from comets and asteroids. “But nothing like this.”

The dust came in a tight stream, like water from a garden hose, and it was moving extraordinarily fast, about 300 km/s (670,000 mph). “This makes it some of the fastest-moving material in the solar system,” says Krueger, “second only to the solar wind.” Fortunately the dust-bits were small, similar in size to particles in cigarette smoke, so they didn’t penetrate the ship’s hull in spite of their extreme velocity.

At first, no one suspected Io. Ulysses was 100 million kilometers from Io when the stream blew by, supposedly beyond the reach of volcanic plumes. Plus, the speed of the dust didn’t make sense. Particles emerge from Io’s vents traveling 1 or 2 km/s, not 300 km/s.

Baffled, researchers considered several possibilities: Could Jupiter’s dark rings be responsible? There’s plenty of dust there, but how could rings manufacture fast-moving jets? Comet Shoemaker-Levy 9 was another suspect. The comet flew so close to Jupiter in 1992 that it was torn apart. Comets are known to produce streams of dust, but not so fast as the stream that hit Ulysses.

NASA’s Galileo spacecraft eventually solved the puzzle. Like Ulysses, Galileo was pelted by dust when it approached Jupiter in 1995. Unlike Ulysses, which merely flew past the giant planet, Galileo settled into orbit. As data accumulated over a period of years, scientists were able to correlate volcanic activity with dust events, and they showed, furthermore, that dust streams were modulated by Io’s orbital motion.

The source was definitely Io.

Regarding the extreme velocity of the dust: “Jupiter is responsible for that,” explains Krueger.

Jupiter is not only a giant planet, but also a giant magnet, which spins once every 9 hours and 55 minutes. Spinning magnetic fields produce electric fields, and the electric fields around Jupiter are intense. Io-dust, like dust on your computer monitor, is electrically charged, so Jupiter’s electric forces naturally accelerate the grains. 300 km/s is no problem.

In 2000 when the Cassini spacecraft sailed past Jupiter en route to Saturn, it too was hit. Cassini’s dust detector is more capable than Ulysses’. In addition to mass, speed, charge and trajectory, it can also measure elemental composition. Cassini found hints of sulfur, silicon, sodium and potassium–all signs of volcanic origin.

“This raises an interesting possibility,” says Krueger. “We can analyze the hot interior of Io from a great distance.” There’s no need to get too close to the sizzling vents when you can catch the ash millions of miles away.

Io dust can even reach Earth, says Krueger, but don’t expect a meteor shower. Bright meteors such as Perseids and Leonids are caused by sand-sized comet dust. Io dust is much smaller. A typical grain is only 10 billionths of a meter wide. If a bit of it disintegrated in Earth’s atmosphere, you probably wouldn’t notice.

End of story? Not quite.

Ulysses visited Jupiter again in early 2004 and once again the craft was pelted. Io’s volcanoes were still at work. But something was wrong: The dust was shooting in the wrong direction.

“Io dust is supposed fly out of Jupiter’s equatorial plane,” says Krueger, “because that’s the way the accelerating electric fields point.” This time Ulysses approached Jupiter’s north pole (75 degrees north latitude to be exact) where no dust should go. Yet the spacecraft was pelted anyway.

Jupiter, it seems, flings Io-dust in every direction, which is hard to understand, says Krueger. Future missions to the giant planet might unravel the mystery. Every blast of dust will remind: we’ve still got a lot to learn.

Original Source: NASA Science Article

Scientists have discovered irregular lumps beneath the icy surface of Jupiter’s largest moon, Ganymede. These irregular masses may be rock formations, supported by Ganymede’s icy shell for billions of years. This discovery comes nearly a year after the orchestrated demise of NASA’s Galileo spacecraft into Jupiter’s atmosphere and more than seven years after the data were collected.

Researchers at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., and the University of California, Los Angeles, report their findings in a paper that will appear in the Aug. 13 issue of the journal Science.

The findings have caused scientists to rethink what the interior of Ganymede might contain. The reported bulges reside in the interior, and there are no visible surface features associated with them. This tells scientists that the ice is probably strong enough, at least near the surface, to support these possible rock masses from sinking to the bottom of the ice for billions of years. But this anomaly could also be caused by piles of rock at the bottom of the ice.

“The anomalies could be large concentrations of rock at or underneath the ice surface. They could also be in a layer of mixed ice and rock below the surface with variations in the amount of rock,” said Dr. John Anderson, a scientist and the paper’s lead author at JPL. “If there is a liquid water ocean inside Ganymede’s outer ice layer there might be variations in its depth with piles of rock at the ocean bottom. There could be topographic variations in a hidden rocky surface underlying a deep outer icy shell. There are many possibilities, and we need to do more studies.”

Dr. Gerald Schubert, co-author at UCLA, said “Although we don’t yet have anything definitive about the depth at this point, we did not expect Ganymede’s ice shell to be strong enough to support these lumpy mass concentrations. Thus, we expect that the irregularities would be close to the surface where the ice is coldest and strongest, or at the bottom of the thick ice shell resting on the underlying rock. It would really be a surprise if these masses were deep and in the middle of the ice shell.”

Ganymede has three main layers. A sphere of metallic iron at the center (the core), a spherical shell of rock (mantle) surrounding the core, and a spherical shell of mostly ice surrounding the rock shell and the core. The ice shell on the outside is very thick, maybe 800 kilometers (497 miles) thick. The surface is the very top of the ice shell. Though it is mostly ice, the ice shell might contain some rock mixed in. Scientists believe there must be a fair amount of rock in the ice near the surface. Variations in this amount of rock may be the source of these possible rock formations.

Scientists stumbled on the results by studying Doppler measurements of Ganymede’s gravity field during Galileo’s second flyby of the moon in 1996. Scientists were measuring the effect of the moon’s gravity on the spacecraft as it flew by. They found unexpected variations.

“Believe it or not, it took us this long to straighten out the anomaly question, mostly because we were analyzing all 31 close flybys for all four of Jupiter’s large moons,” said Anderson. “In the end, we concluded that there is only one flyby, the second flyby of Ganymede, where mass anomalies are evident.”

Scientists have seen mass concentration anomalies on one other moon before, Earth’s, during the first lunar orbiter missions in the 1960s. The lunar mass concentrations during the Apollo moon mission era were due to lava in flat basins. However, scientists cannot draw any similarities between these mass concentrations and what they see at Ganymede.

“The fact that these mass anomalies can be detected with just flybys is significant for future missions,” said Dr. Torrence Johnson, former Galileo project scientist. “With this type of information you could make detailed gravity and altitude maps that allow us to actually map structures within the ice crust or on the rocky surface. Knowing more about the interior of Ganymede raises the level of importance of looking for gravity anomalies around Jupiter’s moons and gives us something to look for. This might be something NASA’s proposed Jupiter Icy Moons Orbiter Mission could probe into deeper.”

The paper was co-authored by Dr. Robert A. Jacobson and Eunice L. Lau of JPL, with Dr. William B. Moore and Jennifer L. Palguta of UCLA. JPL is a division of the California Institute of Technology in Pasadena. JPL designed and built the Galileo orbiter, and operated the mission. For images and information about the Galileo mission, visit http://galileo.jpl.nasa.gov.

Image credit: NASA/JPL
The hottest spot in the solar system is neither Mercury, Venus, nor St. Louis in the summer. Io, one of the four satellites that the Italian astronomer Galileo discovered orbiting Jupiter almost 400 years ago, takes that prize. The Voyager spacecraft discovered volcanic activity on Io over 20 years ago and subsequent observations show that Io is the most volcanically active body in the solar system. The Galileo spacecraft, named in honor of the astronomer Galileo, found volcanic hot spots with temperatures as high as 2,910 Fahrenheit (1,610 Celsius).

Now computer models of volcanic eruptions on Io performed by researchers at Washington University in St. Louis show that the lavas are so hot that they are vaporizing sodium, potassium, silicon and iron and probably other gases as well into its atmosphere.

Using an updated version of MAGMA, a versatile computer program he developed 15 years ago with a Harvard University colleague, Bruce Fegley, Jr., Ph.D., professor of earth and planetary sciences in Arts & Sciences at Washington University in St. Louis, found that some of these elements are vaporized at least partly as single-atom gases. Others are vaporized in different molecular forms, for instance, silicon monoxide, silicon dioxide and iron monoxide.

“Reaction of these gases with sulfur and chlorine species in volcanic gases could lead to the formation of such unusual gases as sodium chloride, potassium chloride, magnesium dichloride and iron dichloride, ” Fegley said.

In 2000, Fegley and former Washington University colleague Mikhail Zolotov, Ph.D., now at Arizona Sate University, predicted formation of sodium chloride and potassium chloride vapor in volcanic gases on Io. Three years later astronomers found sodium chloride gas on Io. However, these observations were not sensitive enough to detect the less abundant potassium chloride vapor.

Now Fegley has found that sodium and potassium in Ionian volcanic gases are being vaporized from the hot lavas. Fegley and research assistant Laura Schaefer of Washington University used data from the Galileo mission and Earth-based observations from high-powered telescopes in their NASA-funded research. They published their results in the May 2004 issue of Icarus, the leading planetary science journal.

“We’re basically doing geology on Io using data from telescopes on Earth, which shows that observations like this can compete with expensive space missions,” said Fegley. “It’s amazing how hot and how volcanically active Io is. It is 30 times more active than Earth. It’s the hottest body outside of the sun in the solar system.”

The innermost of the four major satellites of Jupiter – there are at least 16 – Io gets its high rate of volcanism from tidal interactions with Jupiter, which has the strongest magnetic field of all the planets. Over 100 active volcanoes have been identified on Io. Hotspots there have temperatures as high as 1,600 degrees Celsius. This is several hundred degrees hotter than terrestrial volcanoes like Kilauea in Hawaii, which has a temperature of about 1,000 Celsius (1,830 Fahrenheit).

Fegley and Schaefer found that silicon monoxide is the major silicon-bearing gas over the lavas.

“The interesting thing about this is that astronomers have observed silicon monoxide in other environments in interstellar space, most notably in the atmospheres of cool stars,” said Fegley.

Astronomical observations of actively erupting volcanoes on Io may be able to detect the silicon monoxide gas in its atmosphere.

Fegley and Schaefer recommend an Io volcanic probe mission to directly measure the pressure, temperature and composition of gases of Pele, one of Io’s most active volcanoes. Such an endeavor is “feasible using present technology,” Fegley said. “It would vastly expand our knowledge of the most volcanically active body in the solar system.”

The volcanic probe mission would represent an advance in the effort to unveil some of Io’s mysteries, such as how the satellite, about the size of our own Moon, can maintain its high magma temperatures without being nearly totally molten, and how does Io maintain a strong enough lithosphere to support mountains higher than Mount Everest?

Original Source: WUSTL News Release

Image credit: NASA/JPL
NASA has issued its mission design requirements to three industry teams for a proposed mission to Jupiter and its three icy moons. The requirements are also the first product formulated by NASA’s new Office of Exploration Systems in Washington.

The Jupiter Icy Moons Orbiter is a spacecraft with an ambitious proposed mission that would orbit three planet-sized moons of Jupiter — Callisto, Ganymede and Europa — that may harbor vast oceans beneath their icy surfaces. The mission would be powered by a nuclear reactor and launched sometime in the next decade.

Associate Administrator retired Rear Adm. Craig E. Steidle of NASA’s Office of Exploration Systems said, “The Jupiter Icy Moons Orbiter requirements represent our new way of doing business, tracing exploration strategies to the technology maturation programs that will enable this exciting mission and the other missions that make up Project Constellation.”

The Request for Proposal was released this week to the three previously qualified industry teams led by Boeing, Huntington Beach, Calif.; Lockheed Martin, Denver; and Northrop Grumman, Redondo Beach, Calif. These three companies are currently working under study contracts investigating conceptual designs for the mission. The proposals are due July 16, 2004.

The scope of the initial contract is to co-design the spacecraft through the preliminary design with the government team. A contract modification will be issued after preliminary design to implement the design, to integrate and test the spacecraft and to integrate the spacecraft with the reactor module and mission module. JPL would be responsible for delivering the mission module, which would include instruments procured competitively via a NASA announcement of opportunity. The launch vehicle will be supplied by NASA. The Department of Energy’s Office of Naval Reactors would be responsible for the reactor module. To ensure the technologies demonstrated are consistent and coordinated with the Vision for Space Exploration, Project Constellation is managed within the Office of Exploration Systems.

“Although the Jupiter Icy Moons Orbiter mission may not launch until the next decade, the study of revolutionary new technologies in spacecraft design is underway in the areas of power conversion and heat rejection, electric propulsion, radiation hardened electronics and materials, and telecommunications,” said Karla Clark, industry studies lead and deep space avionics project manager for the Jupiter Icy Moons Orbiter Mission.

Three cross-cutting science themes identified by the NASA- chartered science definition team would drive the proposed Jupiter Icy Moons Orbiter science investigations. The themes are to evaluate the degree to which subsurface oceans are present on these worlds; to study the chemical composition of the moons, including organic materials, and the surface processes that affect them; and to scrutinize the entire Jupiter system, particularly the interactions between Jupiter and the moons’ atmospheres and interiors.

“The scientists have told us what they want,” said John Casani, project manager for the Jupiter Icy Moons Orbiter mission at JPL. “When you consider the five-to-eight year trip to Jupiter, going from one moon to the next, not only flying by but orbiting each moon, this will require a unique nuclear power and electric propulsion system. The large amount of power required for electric propulsion could be used in orbit to power a significantly enhanced suite of instruments not even conceivable with previous power systems.”

The Jupiter Icy Moons Orbiter mission is part of NASA’s Project Prometheus, a program studying a series of initiatives to develop power systems and technologies for space exploration. The Jupiter Icy Moons Orbiter, managed by JPL, would be the first NASA mission utilizing nuclear electric propulsion, which would enable the spacecraft to orbit each of these icy worlds to perform extensive investigations of their makeup, history and potential for sustaining life. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the proposed Jupiter Icy Moons Orbiter mission for NASA’s Office of Exploration Systems, Washington, D.C.

For more information visit: http://spacescience.nasa.gov/missions/prometheus.htm or: NASA JIMO Mission

Original Source: NASA/JPL News Release

Image credit: NASA/JPL
If a University of California, Berkeley, physicist’s vision of Jupiter is correct, the giant planet will be in for a major global temperature shift over the next decade as most of its large vortices disappear.

But fans of the Great Red Spot can rest easy. The most famous of Jupiter’s vortices – which are often compared to Earth’s hurricanes – will stay put, largely because of its location near the planet’s equator, says Philip Marcus, a professor at UC Berkeley’s Department of Mechanical Engineering.

Using whirlpools and eddies for comparison, Marcus bases his forecast on principals learned in junior-level fluid dynamics and on the observation that many of Jupiter’s vortices are literally vanishing into thin air.

“I predict that due to the loss of these atmospheric whirlpools, the average temperature on Jupiter will change by as much as 10 degrees Celsius, getting warmer near the equator and cooler at the poles,” says Marcus. “This global shift in temperature will cause the jet streams to become unstable and thereby spawn new vortices. It’s an event that even backyard astronomers will be able to witness.”

According to Marcus, the imminent changes signal the end of Jupiter’s current 70-year climate cycle. His surprising predictions are published in the April 22 issue of the journal Nature.

Jupiter’s stormy atmosphere has a dozen or so jet streams that travel in alternating directions of east and west, and that can clock speeds greater than 330 miles per hour. As on Earth, vortices on Jupiter that rotate clockwise in the northern hemisphere are considered anticyclones, while those that spin counterclockwise are cyclones. The opposite is true in the southern hemisphere, where clockwise vortices are cyclones and counterclockwise spinners are anticyclones.

The Great Red Spot, located in the southern hemisphere, holds title as Jupiter’s largest anticyclone; spanning 12,500 miles wide, it is large enough to swallow Earth two to three times over.

Unlike the cyclonic storms on Jupiter, Earth’s hurricanes and storms are associated with low-pressure systems and dissipate after days or weeks. The Great Red Spot, in comparison, is a high-pressure system that has been stable for more than 300 years, and shows no signs of slowing down.

About 20 years ago, Marcus developed a computer model showing how the Great Red Spot emerged out of and endured in the chaotic turbulence of Jupiter’s atmosphere. His efforts to explain the dynamics governing it and other vortices on Jupiter led to his current projection of the planet’s impending climate change.

He says the current 70-year cycle began with the formation of three distinct anticyclones – the White Ovals – that developed south of the Great Red Spot in 1939. “The birth of the White Ovals was seen through telescopes on Earth,” he says. “I believe we’re in for a similar treat within the next 10 years.”

Marcus says the first stage of the climate cycle involves the formation of vortex streets which straddle the westward jet streams. Anticyclones form on one side of the street, while cyclones form on the other side, with no two vortices rotating in the same direction directly adjacent to each other.

Most of the vortices slowly decay with turbulence. By stage two of the cycle, some vortices become weak enough to get trapped in the occasional troughs, or Rossby waves, that form in the jet stream. Multiple vortices can get caught in the same trough. When they do, they travel bunched together, and turbulence can easily make them merge. When the vortices are weak, trapping and merging continues until only one pair is left on each vortex street.

The noted disappearance of two White Ovals, one in 1997 or 1998 and a second in 2000, exemplified the merging of the vortices in stage two, and as such, signaled the “beginning of the end” of Jupiter’s current climate cycle, says Marcus.

Why would the merger of vortices affect global temperature? Marcus says the relatively uniform temperature of Jupiter – where the temperatures at the poles are nearly the same as they are at the equator – is due to the chaotic mixing of heat and airflow from the vortices.

“If you knock out a whole row of vortices, you stop all the mixing of heat at that latitude,” says Marcus. “This creates a big wall and prevents the transport of heat from the equator to the poles.”

Once enough vortices are gone, the planet’s atmosphere will warm at the equator and cool at the poles by as much as 10 degrees Celsius in each region, which is stage three of the climate cycle.

This temperature change destabilizes the jet streams, which will react by becoming wavy. The waves steepen and break up, like they do at the beach, but they then roll up into new large vortices in the cycle’s fourth stage. In the fifth and final stage of the climate cycle, the new vortices decrease in size, and they settle into the vortex streets to begin a new cycle.

The weakening of the vortices is due to turbulence and happens gradually over time. It takes about half a century for newly formed vortices to gradually shrink down enough to be caught up in a jet stream trough, says Marcus.

Fortunately, the Great Red Spot’s proximity to the equator saves it from destruction. Unlike Jupiter’s other vortices, the Great Red Spot survives by “eating” its neighboring anticyclones, says Marcus.

Marcus notes that his theory of Jupiter’s climate cycle relies on the existence of a roughly equal number of cyclones and anticyclones on the planet.

Since the telltale signs of vortices are the clouds they create, it was easy to miss the presence of long-lived cyclones, says Marcus. He explains that unlike an anticyclone’s distinct spot, cyclones create patterns of filamentary clouds that are less clearly defined.

“On the face of it, it is easy to think that Jupiter is dominated by anticyclones because their spinning clouds show up clearly as bull’s-eyes,” says Marcus.

In the paper in Nature, Marcus presents a computer simulation showing that the warm center and cooler perimeter of a cyclone creates the appearance of the filamentary clouds. In contrast, anticyclones have cold centers and warmer perimeters. Ice crystals that form in the anticyclone’s center swell up and move to the sides where they melt, creating a darker swirl surrounding a lighter colored center.

Marcus approaches the study of planetary atmospheres from the untraditional viewpoint of a fluid dynamicist. “I’m basing my predictions on the relatively simple laws of vortex dynamics instead of using voluminous amounts of data or complex atmospheric models,” says Marcus.

Marcus says the lesson of Jupiter’s climate could be that small disturbances can cause global changes. However, he cautions against applying the same model to Earth’s climate, which is influenced by many different factors, both natural and manmade.

“Still, it’s important to have different ‘labs’ for climate,” says Marcus. “Studying other worlds helps us better understand our own, even if they are not directly analogous.”

Marcus’s research is supported by grants from the NASA Origins Program, the National Science Foundation Astronomy and Plasma Physics Programs and the Los Alamos National Laboratory.

Original Source: UC Berkeley News Release

Image credit: NASA/JPL
Investigations into lava lakes on the surface of Io, the intensely volcanic moon that orbits Jupiter, may provide clues to what Earth looked like in its earliest phases, according to researchers at the University at Buffalo and NASA’s Jet Propulsion Laboratory.

“When I look at the data, it becomes startlingly suggestive to me that this may be a window onto the primitive history of Earth,” said Tracy K. P. Gregg, Ph.D., assistant professor of geology in the UB College of Arts and Sciences.

“When we look at Io, we may be seeing what Earth looked like when it was in its earliest stages, akin to what a newborn baby looks like in the first few seconds following birth,” she added.

Gregg and Rosaly M. Lopes, Ph.D., research scientist at JPL, gave a presentation about Io’s volcano, Loki, on Tuesday (March 16, 2004) at the Lunar and Planetary Science Conference in Houston.

Scientists have been interested in Loki, considered the most powerful volcano in the solar system, because of debate over whether or not it is an active lava lake, where molten lava is in constant contact with a large reservoir of magma stored in the planet’s crust.

Using models developed to investigate temperature changes on active lava lakes on Earth, Gregg and Lopes have concluded that Loki behaves quite differently from terrestrial lava lakes.

Gregg suggests that Loki and other lava lakes on Io might be more similar volcanologically to fast-spreading mid-ocean ridges on Earth, like the Southern East Pacific Rise.

According to Gregg, plate tectonics on Earth make these features long — as in thousands of kilometers — and narrow — as in less than 10 kilometers wide. Io, on the other hand, has no plate tectonics and a similar release of heat and magma would be circular, like Loki.

“These lava lakes could be an Ionian version of mid-ocean ridges,” functioning the way these ridges do on Earth, spilling huge amounts of lava on its surface, thus generating new crust, she said.

During the most intense periods of its eruption cycle, Gregg said, Loki churns out about 1,000 square meters of lava — about the size of a soccer field — per second.

“All planets start out hot and spend their ‘lifetimes’ trying to get cold,” explained Gregg.

This effort by planets to “chill,” she explained, is an attempt to attain a similar temperature to that of outer space, which is 4 Kelvin, or minus 269 degrees Celsius.

On Earth, she explained, the shifting of the planet’s tectonic plates, which focus the eruption of volcanoes at their boundaries, function to cool down the planet’s surface.

Io never developed plate tectonics because it is stuck in an incessant orbit between Jupiter and Europa, another of the Jovian planet’s moons.

“Io just never grew up,” she said, “since it’s continually being pushed around by Jupiter and Europa.”

But, she added, Earth only developed plate tectonics after it had been in existence for perhaps 200 to 500 million years.

Gregg and Lopes analyzed data obtained by the Galileo spacecraft, which orbited Jupiter for 14 years, finally disintegrating in Jupiter’s atmosphere last fall.

The University at Buffalo is a premier research-intensive public university, the largest and most comprehensive campus in the State University of New York.

Original Source: University at Buffalo News Release

Image credit: NASA
Lately Earth and Jupiter have been approaching one another, and this week the two worlds are only 400 million miles apart. That’s what astronomers call “a close encounter.”

400 million miles is close–on the vast scale of the solar system. Consider Pluto. It’s nearly ten times farther away than Jupiter. Or Saturn. The ringed planet is 800 million miles away. Nevertheless, Saturn looks wonderful right now, and Jupiter is even better.

400 million miles makes Jupiter ten times brighter than Saturn, and twenty-five times brighter than a 1st magnitude star. It outshines everything else in the sky except Venus, the Moon and the Sun.

See for yourself.

Step outside after sunset any night this week and look east. Jupiter is that very bright “star” near the horizon–not to be confused with even brighter Venus in the west. By 9 p.m. Jupiter will be high in the eastern sky, simply dazzling.

On March 4th, the date of closest approach, and March 5th, Jupiter will appear right beside the full Moon in the constellation Leo. So you won’t need a sky map to find Jupiter, just look for the Moon.

If you have a telescope, point it at Jupiter. Even a small ‘scope will reveal Jupiter’s rust-colored cloud belts and its four largest moons. Io, Europa, Callisto and Ganymede look like a dim line of stars straddling the giant planet. Sometimes only two or three moons are visible. That’s because one or two of them are behind Jupiter. Look again later or perhaps tomorrow. The missing moons will come out of hiding as they circle their planet.

The four “Galilean satellites”–so named because they were first observed by Galileo Galilei in 1610–are among the weirdest worlds in the solar system. Io looks like a pizza, and it has active volcanoes that spew sulfurous snow. Europa and Callisto are icy places, hiding, perhaps, the biggest oceans in the solar system beneath their frozen crusts. Ganymede is simply big–larger than Pluto and Mercury, and almost as wide as Mars. If it orbited the sun instead of Jupiter, Ganymede would be considered a full-fledged planet.

Sometimes you can see dark spots creeping across Jupiter. These are shadows cast by the four big moons. Sky & Telescope magazine publishes a schedule of shadow crossings, so you can find out when to look. The crossings are fun to watch through a telescope.

Another thing to look for is Jupiter’s Great Red Spot–a cyclone twice the size of Earth, and at least 100 years old. It swirls across Jupiter’s middle approximately every 10 hours. Again, check Sky & Telescope for viewing times.

First-time observers of Jupiter, squinting through the eyepiece of a small telescope, don’t always believe what they see. The giant planet looks slightly squashed. Is there something wrong with the optics? No, Jupiter really is flattened. The giant planet, 11 times wider than Earth, spins on its axis in only 9 hours and 55 minutes. Speedy rotation gives Jupiter an equatorial bulge. The “squash” is real.

So is the pizza moon, the giant cyclone, the alien oceans. They’re all just 400 million miles away. This is a close encounter you won’t want to miss.

Original Source: NASA Science Story

Image credit: ESA
In a repeat performance of its groundbreaking discovery in 1992, the DUST instrument on board Ulysses has detected streams of dust particles flowing from Jupiter during the recent second encounter with the giant planet.

The dust streams, comprising grains no larger than smoke particles, originate in the fiery volcanoes of Jupiter?s moon Io. The dust stream particles, which carry an electric charge, are strongly influenced by Jupiter’s magnetic field. Electromagnetic forces propel the dust out of the Jovian system, into interplanetary space.

“The recent observations include the most distant dust stream ever recorded – 3.3 AU (nearly 500 million km) from Jupiter!? said Dr. Harald Kr?ger, from the Max-Planck-Institut f?r Kernphysik in Heidelberg. Another unusual feature is that the streams occur with a period of about 28 days. This suggests that they are influenced by solar wind streams that rotate with the Sun. “Interestingly, the most intense peaks show some fine structure which was not the case in 1992?, said Kr?ger, Principal Investigator for the DUST instrument.

Early on in the history of the solar system, as the planets were being formed, small dust particles were much more abundant. These charged grains were influenced by magnetic fields from the early Sun, in much the same way as the dust from Io is affected by Jupiter’s magnetic field today. “By studying the behaviour of these dust stream particles, we hope to gain an insight into processes that led to the formation of the moons and planets in our solar system?, said Richard Marsden, ESA?s Mission Manager for Ulysses. Dust particles carry information about charging processes in regions of Jupiter?s magnetosphere that are difficult to access by other means.

Original Source: ESA News Release

Image credit: NASA/JPL

The team responsible for the Cassini spacecraft’s imaging system have produced the most detailed mosaic image of Jupiter ever created – the whole planet is visible down to a resolution of 60 km. The spacecraft took a series of 27 images over the course of an hour on December 29, 2000. The separate photos were then blended together on a computer to account for Jupiter’s rotation and the movement of the spacecraft.

This true color mosaic of Jupiter was constructed from images taken by the narrow angle camera onboard NASA’s Cassini spacecraft starting at 5:31 Universal time on December 29, 2000, as the spacecraft neared Jupiter during its flyby of the giant planet. It is the most detailed global color portrait of Jupiter ever produced; the smallest visible features are ~ 60 km (37 miles) across. The mosaic is composed of 27 images: nine images were required to cover the entire planet in a tic-tac-toe pattern, and each of those locations was imaged in red, green, and blue to provide true color. Although Cassini’s camera can see more colors than humans can, Jupiter here looks the way that the human eye would see it.

Cassini’s camera is digital, much like today’s popular cameras, and it takes images in each color separately as different spectral filters are rotated in front of its light-sensitive detector. Over an hour was required for this portrait. Jupiter rotated during this time, so the face it presented to the camera, and the lighting on its moving clouds, were constantly changing. In order to assemble a seamless mosaic, each image was first digitally re-positioned to reflect the planet’s appearance at the instant the first exposure was taken. Then, the lighting variation across each image was removed, and the mosaic was re-illuminated by a computer-generated ‘Sun’ from a direction that allowed all imaged portions to appear in sunlight at once. The result, which was slightly contrast-enhanced to bring out subtleties in the Jupiter atmosphere, is a view that the spacecraft would have had at the same distance from the planet but ~ 80 degrees solar phase.

Everything visible on the planet is a cloud. The parallel reddish-brown and white bands, the white ovals, and the large Great Red Spot persist over many years despite the intense turbulence visible in the atmosphere. The most energetic features are the small, bright clouds to the left of the Great Red Spot and in similar locations in the northern half of the planet. These clouds grow and disappear over a few days and generate lightning. Streaks form as clouds are sheared apart by Jupiter’s intense jet streams that run parallel to the colored bands. The prominent dark band in the northern half of the planet is the location of Jupiter’s fastest jet stream, with eastward winds of 480 km (300 miles) per hour. Jupiter’s diameter is eleven times that of Earth, so the smallest storms on this mosaic are comparable in size to the largest hurricanes on Earth.

Unlike Earth, where only water condenses to form clouds, Jupiter’s clouds are made of ammonia, hydrogen sulfide, and water. The updrafts and downdrafts bring different mixtures of these substances up from below, leading to clouds at different heights. The brown and orange colors may be due to trace chemicals dredged up from deeper levels of the atmosphere, or they may be byproducts of chemical reactions driven by ultraviolet light from the Sun. Bluish areas, such as the small features just north and south of the equator, are areas of reduced cloud cover, where one can see deeper.

Original Source: Arizona University News Release

Image credit: NASA/JPL

NASA’s Galileo spacecraft was intentionally crashed into Jupiter on Sunday, ending 14 years of service to science and exploration. The spacecraft entered Jupiter’s thick atmosphere and disintegrated at 1857 GMT (2:57pm EDT), but the last signals arrived at Earth nearly an hour later because of the great distance to Jupiter. At the end of its mission, Galileo lacked the fuel to escape the Jovian system so scientists decided to crash it into Jupiter to avoid contaminating any potential life on Europa, which is believed to have liquid water oceans under a thick sheet of ice.

The Galileo spacecraft’s 14-year odyssey came to an end on Sunday, Sept. 21, when the spacecraft passed into Jupiter’s shadow then disintegrated in the planet’s dense atmosphere at 11:57 a.m. Pacific Daylight Time. The Deep Space Network tracking station in Goldstone, Calif., received the last signal at 12:43:14 PDT. The delay is due to the time it takes for the signal to travel to Earth.

Hundreds of former Galileo project members and their families were present at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., for a celebration to bid the spacecraft goodbye.

“We learned mind-boggling things. This mission was worth its weight in gold,” said Dr. Claudia Alexander, Galileo project manager.

Having traveled approximately 4.6 billion kilometers (about 2.8 billion miles), the hardy spacecraft endured more than four times the cumulative dose of harmful jovian radiation it was designed to withstand. During a previous flyby of the moon Amalthea in November 2002, flashes of light were seen by the star scanner that indicated the presence of rocky debris circling Jupiter in the vicinity of the small moon. Another measurement of this area was taken today during Galileo’s final pass. Further analysis may help confirm or constrain the existence of a ring at Amalthea’s orbit.

“We haven’t lost a spacecraft, we’ve gained a steppingstone into the future of space exploration,” said Dr. Torrance Johnson, Galileo project scientist.

The spacecraft was purposely put on a collision course with Jupiter because the onboard propellant was nearly depleted and to eliminate any chance of an unwanted impact between the spacecraft and Jupiter’s moon Europa, which Galileo discovered is likely to have a subsurface ocean. Without propellant, the spacecraft would not be able to point its antenna toward Earth or adjust its trajectory, so controlling the spacecraft would no longer be possible. The possibility of life existing on Europa is so compelling and has raised so many unanswered questions that it is prompting plans for future spacecraft to return to the icy moon.

Galileo was launched from the cargo bay of Space Shuttle Atlantis in 1989. The exciting list of discoveries started even before Galileo got a glimpse of Jupiter. As it crossed the asteroid belt in October 1991, Galileo snapped images of Gaspra, returning the first ever close-up image of an asteroid. Less then a year later, the spacecraft got up close to yet another asteroid, Ida, revealing it had its own little “moon,” Dactyl, the first known moon of an asteroid. In 1994 the spacecraft made the only direct observation of a comet impacting a planet– comet Shoemaker-Levy 9’s collision with Jupiter.

The descent probe made the first in-place studies of the planet’s clouds and winds, and it furthered scientists’ understanding of how Jupiter evolved. The probe also made composition measurements designed to assess the degree of evolution of Jupiter compared to the Sun.

Galileo made the first observation of ammonia clouds in another planet’s atmosphere. It also observed numerous large thunderstorms on Jupiter many times larger than those on Earth, with lightning strikes up to 1,000 times more powerful than on Earth. It was the first spacecraft to dwell in a giant planet’s magnetosphere long enough to identify its global structure and to investigate the dynamics of Jupiter’s magnetic field. Galileo determined that Jupiter’s ring system is formed by dust kicked up as interplanetary meteoroids smash into the planet’s four small inner moons. Galileo data showed that Jupiter’s outermost ring is actually two rings, one embedded within the other.

Galileo extensively investigated the geologic diversity of Jupiter’s four largest moons: Ganymede, Callisto, Io and Europa. Galileo found that Io’s extensive volcanic activity is 100 times greater than that found on Earth. The moon Europa, Galileo unveiled, could be hiding a salty ocean up to 100 kilometers (62 miles) deep underneath its frozen surface containing about twice as much water as all the Earth’s oceans. Data also showed Ganymede and Callisto may have a liquid-saltwater layer. The biggest discovery surrounding Ganymede was the presence of a magnetic field. No other moon of any planet is known to have one.

The prime mission ended six years ago, after two years of orbiting Jupiter. NASA extended the mission three times to continue taking advantage of Galileo’s unique capabilities for accomplishing valuable science. The mission was possible because it drew its power from two long-lasting radioisotope thermoelectric generators provided by the Department of Energy.

“The mission was a testimonial to the persistence of NASA even through tremendous challenges. It was a phenomenal mission,” said Sean O’Keefe, NASA administrator.

Original Source: NASA/JPL News Release