Pluto Probe helps unravel secrets of Jupiter’s mysterious magnetotail

November 14th, 2007 - 1:59 am ICT by admin  
The encounter occurred as the spacecraft rounded the gas-giant in February 2007 for a gravity assist to help speed its journey to the edge of the solar system.

During the flyby, the Solar Wind Around Pluto (SWAP) instrument aboard the spacecraft measured plasma populations inside the planet’s magnetosphere on an orbit that has never been travelled before.

That orbit carried the spacecraft from the planet back a hundred million miles deep into the magnetotail, the portion of the magnetosphere dragged away from the Sun by the flow of the million mile-per-hour solar wind.

SWAP gathered data from solar wind observations upstream of Jupiter, through the closest approach encounter, and back to about 2,500 Jovian radii (about 100 million miles) at the boundary of the magnetotail, called the magnetopause.

Data showed that the inner magnetotail contained very hot ions - hotter than the top of SWAP’s 7.5-kilovolt energy per charge range - that evolved to cooler and slower flows down the tail, beginning at about 100 Jovian radii; these flows were highly variable in flux and energy.

Findings also revealed a complicated structure in the magnetotail with large blobs, or plasmoids, of magnetically influenced plasma drifting down the tail at a relatively slow rate of speed.

As the distance from the planet increased, the magnetotail became more highly structured with gradual variations in the plasma and sharp boundaries (discontinuities) between plasma regimes.

Previous examinations of Jupiter’s magnetotail were limited to measurements very close to the planet and few very brief encounters at even greater distances.

“This was an absolutely fabulous trajectory for doing new science; the spacecraft went almost straight down the middle of the largest cohesive structure in the solar system,” said Dr. David J. McComas, SWAP principal investigator and senior executive director of the Space Science and Engineering Division at Southwest Research Institute.

“We could actually see the structure of the magnetotail and watch its evolution with distance for the first time,” he said.

Dr. McComas said the SWAP observations also revealed an unexpected component in the material flowing away from Jupiter.

In addition to the volcanic material released from Io and material entering the magnetotail from the solar wind, the team found intense bursts of ionospheric hydrogen and H3+, which could only be coming from Jupiter’s atmosphere.

“It’s clear there’s significant escape of 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 Dr. McComas.

He said the New Horizons’ encounter with Jupiter has also raised some new questions.

“In addition to seeing flows move down the magnetotail, we saw them sometimes move across it. As Jupiter has the largest and most powerful magnetosphere in the solar system, everything we can learn about this and other mysteries could have implications for the other planets,” he said.

The paper, “Diverse Plasma Populations and Structures in Jupiter’s Magnetotail,” will be published in the Oct. 12 issue of Science. (ANI)

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