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Posted on 10/19/2007 2:30:40 AM PDT by Swordmaker
NASA's Pluto-bound spacecraft, New Horizons, recently surfed a long tail of charged particles trailing behind Jupiter. Observations from that wild ride revealed enormous bobbing bubbles of charged particles, or "plasma," and showed that the structure of the planet's tadpole-shaped "magnetotail" is surprisingly varied.
The findings, detailed in two reports in the Oct. 9 issue of the journal Science, could help scientists understand the protective magnetic environment surrounding Earth and other planets.
"If we understand our Jupiter better, we will be able to further understand the extrasolar 'hot Jupiters' of other stars," Norbert Krupp, an astronomer at the Max Planck Institute for Solar System Research in Germany who was not involved in the studies, wrote in a related Science article.
Blowing bubbles
In the space surrounding many of the planets in our solar system, there is an ongoing struggle between the magnetic fields of those planets and fast-moving charged particles of the sun's solar wind. The region around a planet where the magnetic field is strong enough to slow down or even repel the solar wind is called the magnetosphere.
The Jovian magnetosphere is enormous. It has a diameter 200 times that of Jupiter itself and is the largest cohesive structure in the solar system. Despite Jupiter's great distance from us, "If you could 'see' the magnetosphere of Jupiter from Earth, it would be about the size of the full Moon," said Ralph McNutt, a senior scientist at John Hopkins University's Applied Physics Laboratory and a lead author on one of the studies.
The side of Jupiter's magnetosphere facing the sun gets squashed by the barrage of oncoming solar-wind particles, but the opposite side is distended like the tail of a comet.
As part of a slingshot maneuver to shorten its journey toward Pluto, New Horizons entered Jupiter's magnetosphere in February 2007 and journeyed down the magnetotail for more than a hundred million miles—longer than any other spacecraft that had visited before.
Inside, New Horizons whizzed past relatively slow moving blobs of plasma, or "plasmoids," that bobbed along inside the magnetotail, guided along by Jupiter's magnetic field.
Scientists think the bubbles are formed from material ejected by Io, a Jovian satellite and the most volcanically active body in the solar system. Once ejected, the particles that make up Io's prodigious debris—the moon spews about 1 metric ton of material per second—are stripped of their electrons by particles in Jupiter's magnetosphere and become captured by the magnetosphere. The snared particles linger around Jupiter like a cloud.
McNutt and his teammates propose that Io's captured particles stretch Jupiter's magnetic field lines like rubber bands, and that occasionally, the field lines snap back into place in "magnetic reconnection" events.
Like elastic thread slicing through gelatin, scientists think the snapping field lines carve out huge chunks of the plasma blobs around Jupiter. These chunks are the plasmoids.
The snapping motion also imparts energy to these plasma bubbles and provides the acceleration needed to propel them down Jupiter's magnetotail.
Unusually structured
New Horizons also detected another class of very hot charged particles hurtling down the magnetotail, which cooled and slowed as they moved away from the planet. Some of the particles originated from Io, but others came from the solar wind and Jupiter's atmosphere. The last source was a surprise to scientists.
"It's clear there's a significant escape of the material from the planet because the brightest burst we see turns out to be material that's largely from Jupiter, not from the solar wind or Io," said David McComas, the principal investigator of New Horizons' Solar Wind Around Pluto (SWAP) instrument and lead author of the other Science study.
The spacecraft also found that, in contrast to Earth's tail, the Jovian magnetotail is surprisingly structured, containing both gradual variations and sharp boundaries in the plasma density.
"There are reports of observations of the Earth's tail as far as about 1,000 Earth radii downstream by the Pioneer 7 spacecraft, but these were intermittent and the structure was certainly not as well ordered" as Jupiter, McNutt said.
Jupiter's magnetotail is long, but it is not infinite. At some point, the gas planet's influence is no longer felt and the magnetotail tapers out, blending into the solar wind.
The plasmoids likely lose their shape as well at those distances, McNutt said, and their particles probably merge with those from the sun.
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Thanks to Sunken Civ for the heads up...
I’m calling a penalty on the writer for overuse of quotation marks, especially for “plasma” and “plasmoid”. ‘Cuz, you know, no one’s EVER heard of plasma before. ;)
"If we understand our Jupiter better, we will be able to further understand the extrasolar 'hot Jupiters' of other stars," Norbert Krupp, an astronomer at the Max Planck Institute for Solar System Research in Germany who was not involved in the studies, wrote in a related Science article....like, for example, how they wound up so close to their stars that they orbit in a matter of hours? :')
Are “you” “sure” of “that”?
Physics NewsA sodium nebula around Jupiter may be the largest object ever recorded on film. A group of astronomers at Boston University, working at the McDonald Observatory in Texas, have detected a neutral cloud of sodium out to distances beyond 400 Jovian radii. The Boston astronomers believe that the shape of the nebula will provide information about Jupiter's magnetosphere and that their technique of measuring non-spherical neutral clouds may be applicable to the study of other planetary magnetospheres.
Phillip F. Schew
November 27, 1990Physics NewsAstronomers have previously known of a sodium cloud which precedes the moon Io in its orbit around Jupiter. The cloud is believed to arise from slow escape of sodium from Io. Now the Galileo spacecraft is providing details of another sodium feature at Io, more of a fast-escaping spray or jet, thought to come about when Io plows through Jupiter's potent magnetic field, a process which induces mega-amp currents through Io's atmosphere... New pictures, reported by scientists at the University of Colorado... and Boston University (Jody Wilson), localize the source of the sodium to a region smaller than Io's diameter, suggesting that Io's atmosphere might not be global; that is, the atmosphere might be patchy and not extend all the way to the poles.
Phillip F. Schewe and Ben Stein
November 9, 1999
Joint News ReleaseBoston University astronomers announced today the discovery of an enormous tail of sodium gas stretching to great distances from the moon. The observations were made at the McDonald Observatory in Fort Davis, Texas, on nights following the Leonid meteor shower of November 1998. The tail of sodium gas was seen to distances of at least 500,000 miles from the moon, changing its appearance over three consecutive nights... Ten years ago, groundbased telescopes revealed that sodium gas (Na) was in the lunar atmosphere, an element that can be used to trace the shape and behavior of such a thin atmosphere... The BU team considered several theories that could explain these unusual features, ruling out a comet, the impact of Leonid meteors upon dust in the solar system, and even possible instrumentation problems... [T]he August observations without meteors and the November observations with meteors imply that the daily flux of micrometeors that strikes the moon's surface creates an extended tail at all times; it was just so enhanced during the strong Leonid storm that it was observed rather easily.
Boston University
Center for Space Physics
and American Geophysical Union
1 June 1999
Note: this topic is from 10/19/2007. Thanks Swordmaker.
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