Category: Jupiter

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

Image credit: NASA/JPL

We’re only days away until Galileo’s final plunge into Jupiter on September 21. Nearly out of fuel, the spacecraft was put onto a collision course with Jupiter to prevent it from accidentally crashing into Europa and potentially contaminating it with Earth-based bacteria. The entry point on Jupiter will be 1/4 of a degree south of its equator and it will strike the planet at 174,000 km/h – obviously it’ll be destroyed almost instantly. Scientists hope to retrieve every piece of data they can, but the radiation will intensify to immense levels as the spacecraft nears the planet, so it might not be possible.

In the end, the Galileo spacecraft will get a taste of Jupiter before taking a final plunge into the planet’s crushing atmosphere, ending the mission on Sunday, Sept. 21. The team expects the spacecraft to transmit a few hours of science data in real time leading up to impact.

The spacecraft has been purposely put on a collision course with Jupiter 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. The long-planned impact is necessary now that the onboard propellant is nearly depleted.

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.

“It has been a fabulous mission for planetary science, and it is hard to see it come to an end,” said Dr. Claudia Alexander, Galileo project manager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “After traversing almost 3 billion miles and being our watchful eyes and ears around Jupiter, we’re keeping our fingers crossed that, even in its final hour, Galileo will still give us new information about Jupiter’s environment.”

Although scientists are hopeful to get every bit of data back for analysis, the likelihood of getting anything is unknown because the spacecraft has already endured more than four times the cumulative dose of harmful jovian radiation it was designed to withstand. The spacecraft will enter an especially high-radiation region again as it approaches Jupiter.

Launched in the cargo bay of Space Shuttle Atlantis in 1989, the mission has produced a string of discoveries while circling the solar system’s largest planet, Jupiter, 34 times. Galileo was the first mission to measure Jupiter’s atmosphere directly with a descent probe and the first to conduct long-term observations of the jovian system from orbit.

It found evidence of subsurface liquid layers of salt water on Europa, Ganymede and Callisto and it examined a diversity of volcanic activity on Io. Galileo is the first spacecraft to fly by an asteroid and the first to discover a moon of an asteroid.

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.

From launch to impact, the spacecraft has traveled 4,631,778,000 kilometers (about 2.8 billion miles).

Its entry point into the giant planet’s atmosphere is about 1/4 degree south of Jupiter’s equator. If there were observers floating along at the cloud tops, they would see Galileo streaming in from a point about 22 degrees above the local horizon. Streaming in could also be described as screaming in, as the speed of the craft relative to those observers would be 48.2 kilometers per second (nearly 108,000 miles per hour). That is the equivalent of traveling from Los Angeles to New York City in 82 seconds. In comparison, the Galileo atmospheric probe, aerodynamically designed to slow down when entering, and parachute gently through the clouds, first reached the atmosphere at a slightly more modest 47.6 kilometers per second (106,500 miles per hour).

“This is a very exciting time for us as we draw to a close on this historic mission and look back at its science discoveries. Galileo taught us so much about Jupiter but there is still much to be learned, and for that we look with promise to future missions,” said Dr. Charles Elachi, director of JPL.

Original Source: NASA/JPL News Release

Image credit: NASA/JPL

Time is running out for NASA’s Galileo spacecraft. After eight years of loyal service imaging Jupiter and its moons, NASA controllers have aimed it at the gas giant. On September 21, 2003, Galileo will crash into Jupiter and be destroyed; this will prevent any chance the spacecraft will unintentionally crash into Europa and contaminate the liquid ocean. NASA is planning a series of live press conferences to explain the end of the mission and discuss Galileo’s discoveries.

Following eight years of capturing dramatic images and surprising science from Jupiter and its moons, NASA’s Galileo mission draws to a close September 21 with a plunge into Jupiter’s atmosphere. Following eight years of capturing dramatic images and surprising science from Jupiter and its moons, NASA’s Galileo mission draws to a close September 21 with a plunge into Jupiter’s atmosphere.

NASA has scheduled a Space Science Update (SSU) at 2 p.m. EDT, Wednesday., September 17, in the James E. Webb Auditorium at NASA headquarters, 300 E St. S.W., Washington. Panelists will discuss the historic mission, engineering challenges, science highlights and plans for Galileo’s impact with Jupiter’s atmosphere.

The SSU will be carried live on NASA Television with two-way question-and-answer capability from participating agency centers. NASA TV is broadcast on AMC-9, transponder 9C, C-Band, located at 85 degrees west longitude. The frequency is 3880 MHz. Polarization is vertical, and audio is monaural at 6.80 MHz. Audio of the SSU is available on voice circuit from the Kennedy Space Center at: 321/867-1220.

SSU participants:

# Dr. Colleen Hartman, director, Solar System Exploration Division, NASA Headquarters.
# Dr. Claudia Alexander, Galileo project manager, NASA Jet Propulsion Laboratory (JPL), Pasadena, Calif.
# Dr. Michael J.S. Belton, Team Leader, Galileo Solid State Imaging Team, Emeritus Astronomer, National Optical Astronomy Observatories, Tucson, Ariz.
# Dr. Don Williams, principal investigator, Galileo heavy ion counter, The Johns Hopkins University, Applied Physics Laboratory, Laurel, Md.
# Jim Erickson, Mars Exploration Rover Mission Manager and former Galileo project manager, JPL.

The spacecraft was put on a collision course with Jupiter’s atmosphere to eliminate any chance of impact of the moon Europa, which Galileo discovered is likely to have a subsurface ocean. The team expects the spacecraft to transmit a few hours of science measurements in real time, leading up to impact on Sunday, September 21. The maneuver is necessary, since onboard propellant is nearly depleted. Without propellant, the spacecraft would not be able to point its antenna toward Earth nor adjust its flight path, so controlling the spacecraft would no longer be possible.

From 4:00 to 5:00 p.m. EDT, September 21, JPL will provide live commentary from the mission control room and footage of the countdown clock as Galileo nears its final moments. The televised special will feature two panels. One will include former project managers, and the other former project scientists.

Live satellite interview opportunities with project personnel are available Friday, September 19. To book a time, please contact Jack Dawson at: 818/354-0040.

Launched by the Space Shuttle Atlantis in 1989, the mission produced a string of discoveries while circling Jupiter, the solar system’s largest planet, 34 times. Galileo was the first spacecraft to directly measure Jupiter’s atmosphere with a probe and the first to conduct long-term observations of the Jovian system from orbit.

Galileo found evidence of subsurface liquid layers of salt water on Jupiter’s moons Europa, Ganymede and Callisto, and it detected extraordinary levels of volcanic activity on Io. Galileo was the first spacecraft to fly by an asteroid and the first to discover the moon of an asteroid. Galileo’s prime mission ended six years ago after two years orbiting Jupiter. NASA extended the mission three times to take advantage of Galileo’s unique science capabilities.

The September 17 SSU and September 21 end of mission event will be Web cast live at:

http://www.jpl.nasa.gov/webcast/galileo/
Additional information about the mission and Galileo’s discoveries is available at:

http://galileo.jpl.nasa.gov
For information about NASA on the Internet, visit:

http://www.nasa.gov

Original Source: NASA News Release

Image credit: UBC

A team of Canadian astronomers have discovered even more new satellites for Jupiter, giving the giant planet a total of 61 moons – 21 were discovered just this year. These new satellites are harder to detect because they’re only 1-5 kilometres across and have wide, irregular orbits around Jupiter. The team took a mosaic of images around the entire sky of Jupiter, and then used a computer to search for points of light that had the motion of a Jovian moon.

They were small and hard to find, but with the help of some new telescopic equipment and cameras, UBC professor Brett Gladman, UBC postdoctoral researcher Lynne Allen, and Dr. J.J. Kavelaars of the National Research Council of Canada have discovered nine previously unknown moons of Jupiter. So far this year, 21 new Jupiter moons have been identified.

The discovery of the distant satellites, announced today at the annual meeting of the Canadian Astronomical Society, boosts the number of known moons on Jupiter to 61 — more moons than any other planet in the solar system.

“The discovery of these small satellites is going to help us understand how Jupiter and the other giant planets formed,” said Gladman, a Canada Research Chair in Planetary Astronomy.

The new satellites were a challenge to detect because most are only about 1-5 kilometers in size. The feeble amounts of light they reflect back to earth must compete against the glare of brilliant Jupiter. Their small size and distance from the Sun prevent the satellites from shining any brighter than 24th magnitude, about 100 million times fainter than can be seen with the unaided eye. To locate these new moons, Gladman’s team used the new Megaprime mosaic of CCD cameras at the 3.6m Canada-France-Hawaii telescope on Mauna Kea, Hawaii.

The mosaic camera enabled the team to take three images of the entire sky around Jupiter. They used computer algorithms to search the images for the faint points of light moving across the sky as moons should.

Because moons can sometimes appear in front of distant stars or lost in the light scattered from the planet, to find them requires painstakingly repeating the search several times. The team undertook the task between February and April 2003.

International members of the jovian search team include Cornell University astronomers Phil Nicholson, Joseph A. Burns, and Valerio Carruba, Jean-Marc Petit of the Observatoire de Besancon, and Brian Marsden and Matthew Holman of the Harvard-Smithsonian Center for Astrophysics.

Original Source: UBC News Release

Image credit: University of Hawaii

Astronomers from the University of Hawaii have discovered six new moons for Jupiter, pushing the planet’s satellite count to 58 – the largest group of moons in the Solar System. These aren’t terribly big moons, though, only a kilometer or so across. The moons were discovered as part of an ongoing search using the world’s largest digital cameras at the Subaru and Canada-France-Hawaii telescopes atop Mauna Kea.

The majority of the new satellites were first seen in early February 2003 by Scott S. Sheppard and David C. Jewitt from the Institute for Astronomy, University of Hawaii along with Jan Kleyna of Cambridge University. The satellites were detected using the world’s two largest digital cameras at the Subaru (8.3 meter diameter) and Canada-France-Hawaii (3.6 meter diameter) telescopes atop Mauna Kea in Hawaii. Both telescopes and their imaging cameras represent the latest technology has to offer. Recoveries were performed at the University of Hawaii 2.2 meter with help from Yanga Fernandez and Henry Hsieh also from the University of Hawaii. Brian Marsden of the Harvard-Smithsonian Center for Astrophysics performed the orbit fitting for the new satellites.

The first 7 satellites were formally announced by the International Astronomical Union on Circular No. 8087 on March 4, 2003 while the eighth was announced on Circular No. 8088 on March 6, the 9th through 12th on Circular No. 8089 on March 7, S/2003 J13 through J20 were announced in April, and S/2003 J21 in May*. Except for S/2003 J20, all the new Jupiter satellites appear to have distant retrograde orbits (ie. their orbital rotation is opposite to Jupiter’s rotation) like the majority of the known irregular satellites of Jupiter. The satellite S/2003 J20 appears to be a prograde satellite dynamically distinct from any other known Jupiter satellite.

Original Source: IFA News Release

Image credit: NASA

A team of French and American astronomers have discovered the presence of salt (NaCl) in Io’s atmosphere. They think that the salt was ejected into the Jovian moon’s atmosphere by the many volcanos that ceaselessly bubble across its surface. The atmosphere of Io has been studied for several years now, first observed closely by the Voyager spacecraft, but this is the first time it’s been found to contain good old “table salt”.

The atmosphere of Jupiter’s moon Io is one of the most peculiar of the Solar System. In 1979, theVoyager spacecraft revealed active volcanism (Figure 1, left) at the surface of the satellite and discovered a local, tenuous SO2 atmosphere. Since 1990, millimeter-wave observations acquired at IRAM (French-German-Spanish telescope) and UV observations with HST provided a somewhat more detailed description of this atmosphere. The typical surface pressure is about 1 nanobar, and, in a unique fashion in the Solar System, the atmosphere exhibits strong horizontal variations, being apparently concentrated in an equatorial band.The main atmospheric compounds are SO2, SO and S2. The atmosphere is probably produced, on the one hand by direct volcanic output, and on the other hand by the sublimation of SO2 ices that cover Io’s surface.

However, it has been long suspected than Io’s atmosphere must contain other chemical species. As early as 1974, visible imaging and spectroscopy revealed a “cloud” of atomic sodium (Figure 1, right), roughly centered about Io’s orbit. Detailed subsequent studies of this cloud indicated a complex structure, including notably “fast sodium” features, for the production of which the role of molecular ions (NaX+ ) was evidenced. These discoveries naturally raised the question of the origin of sodium in Io’s environment. From the brightness of the optical emissions of Na, one can estimate that about 1026-1027 sodium atoms leave Io each second.

In 1999, chlorine in atomic and ionized form was discovered around Io, with an abundance comparable to that of sodium (while the cosmochemical abundance of Na is about 15 times that of Cl). This suggests a common origin, NaCl being a natural plausible parent of both. At the same time, on the basis of thermochemical equilibrium calculations, NaCl was proposed to be an important compound of Io’s volcanic magmas, with an abudance relative to SO2 as high as several percent.

Based on these discoveries and predictions, an observing campaign was conducted by E. Lellouch, from Paris Observatory, and several French and American colleagues at the IRAM 30-m radiotelescope in January 2002. Two rotational lines of NaCl at 143 and 234 GHz were unambiguously detected (Figure 2.). Because the vapor pressure of this salt is entirely negligible, NaCl cannot be in sublimation equilibrium with Io’s surface and its presence must directly result from continuous volcanic output. It appears to be a minor armospheric species. The most plausible physical model depicts the NaCl atmosphere as more localized than SO2, due to its very short lifetime (a few hours at most), and probably restricted to the volcanic centers. The local NaCl abundance in this model is 0.3-1.3 % of SO2, significantly lower than predicted. From the line strengths, volcanic emission rates of (2-8)x1028 NaCl molecules per second can be derived. According to photochemical and escape models, only a small fraction of these molecules escape from Io (about 0.1 %). A somewhat larger amount (1-2 %) leaves Io in atomic form after being photolyzed to Na and Cl. The vast majority of the volcanically-emitted NaCl molecules fall back to the surface where they condense out, potentially contributing to the white color of some of Io’s terrains. In conclusion, it appears that NaCl provides an importante source of sodium and chlorine in Io’s environment; however the precise chemical nature of the NaX+ molecular ions remains to be elucidated.

Original Source: Paris Observatory News Release

Image credit: NASA

The final images that the Galileo spacecraft will take of Jupiter’s moon Io were released today. They showcase crumbling crater slopes and the surface deposits from recent eruptions. Galileo also discovered 13 previously unknown hotspots on the moon’s surface, bringing the total number to 120; many more than anticipated. Galileo will make one final pass of another moon, Amalthea, before crashing into Jupiter in September, 2003.

The final images are in, and the resulting portrait of Jupiter’s moon Io, after a challenging series of observations by NASA’s Galileo spacecraft, is a peppery world of even more plentiful and diverse volcanoes than scientists imagined before Galileo began orbiting Jupiter in 1995.

Now that Galileo’s observations of Io have ended, scientists are focusing on trying to understand the big picture of how Io works by examining details.

Thirteen previously unknown active volcanoes dot infrared images from Galileo’s final successful flyby of Io, volcanologist Dr. Rosaly Lopes of NASA’s Jet Propulsion Laboratory reported today at the spring meeting of the American Geophysical Union in Washington, D.C.

That brings the total number of known Ionian hot spots to 120. Galileo images revealed 74 of them.

“We expected maybe a dozen or two,” said Dr. Torrence Johnson, Galileo project scientist at JPL in Pasadena, Calif. That expectation was based on discoveries by NASA’s Voyager spacecraft in 1979 and 1980, and subsequent ground-based observations.

“The volcanoes on Io have displayed an assortment of eruption styles, but recent observations have surprised us with the frequency of both giant plumes and crusted-over lakes of molten lava,” said planetary scientist Dr. Alfred McEwen of the University of Arizona, Tucson.

Galileo’s latest images, which also show tall slopes crumbling and surface deposits from two eruptions’ recent giant plumes, are available online from JPL at http://www.jpl.nasa.gov/images/io and from the University of Arizona Lunar and Planetary Laboratory at http://pirlwww.lpl.arizona.edu/Galileo/Releases .

Some high-resolution views taken as Galileo skimmed past Io on Oct. 16, 2001, are aiding analysis of the connection between volcanism and the rise and fall of mountains on Io. Few of Io’s volcanoes resemble the crater-topped volcanic peaks seen on Earth and Mars, said planetary scientist Dr. Elizabeth Turtle of the University of Arizona. Most of Io’s volcanic craters are in relatively flat regions, not near mountains, but nearly half of the mountains Io does have sit right beside volcanic craters.

“It appears that the process that drives mountain-building — perhaps the tilting of blocks of crust — also makes it easier for magma to get to the surface,” Turtle said. She showed a new image revealing that material slumping off a mountain named Tohil Mons has not piled up in a crater below, suggesting that the crater floor has been molten more recently than any landslides have occurred. Galileo’s infrared-mapping instrument has detected heat from the crater, indicating an active or very recent eruption.

From the analysis of Galileo’s observations, scientists are developing an understanding of how that distant world resurfaces itself differently than our world does.

“On Earth, we have large-scale lateral transport of the crust by plate tectonics,” McEwen said. “Io appears to have a very different tectonic style dominated by vertical motions. Lava rises from the deep interior and spreads out over the surface. Older lavas are continuously buried and compressed until they must break, with thrust faults raising the tall mountains. These faults also open new pathways to the surface for lava to follow, so we see complex relations between mountains and volcanoes, like at Tohil.”

“Io is a weird place,” Johnson said. “We’ve known that since even before Voyager, and each time Galileo has given us a close look, we get more surprises. Galileo has vastly increased our understanding of Io even though the mission was not originally slated to study Io.”

Extensions to Galileo’s original two-year orbital mission included six swings close to Io, where exposure to Jupiter’s intense radiation belts stresses electronic equipment on board the spacecraft. Researchers presented some results today from two Io encounters in the second half of 2001. Observations were not made successfully during Galileo’s final Io flyby, in January 2002, because effects of the radiation belts put the spacecraft into a precautionary standby mode during the crucial hours of the encounter.

Galileo will make its last flyby of a moon when it passes close to Amalthea, a small inner satellite of Jupiter, on November 5. No imaging is planned for that flyby. With fuel for altering its course and pointing its antenna nearly depleted, the long-lived spacecraft will then loop one last time away from Jupiter and perish in a final plunge into Jupiter’s atmosphere in September 2003.

Additional information about Galileo, Jupiter and Jupiter’s moons is available online at http://galileo.jpl.nasa.gov . JPL, a division of the California Institute of Technology in Pasadena, manages Galileo for NASA’s Office of Space Science, Washington, D.C.

Original Source: NASA/JPL News Release