From: LARRY KLAES (ljk4_at_msn.com)
Date: Tue Oct 23 2007 - 11:08:53 PDT
>From: Lynn Cominsky <lynnc_at_universe.sonoma.edu>
>To: lynnc_at_universe.sonoma.edu
>Subject: SwRI: Jovian magnetosphere circulation differs from Earth's
>Date: Tue, 23 Oct 2007 09:41:44 -0700
>
>THE FOLLOWING RELEASE WAS RECEIVED FROM THE SOUTHWEST RESEARCH INSTITUTE,
>IN SAN ANTONIO, TEXAS, AND IS FORWARDED FOR YOUR
>INFORMATION. (FORWARDING DOES NOT IMPLY ENDORSEMENT BY THE AMERICAN
>ASTRONOMICAL SOCIETY.) Lynn Cominsky, American Astronomical Society
>lynnc_at_universe.sonoma.edu 1-707-664-2655
>
>New theory proposes Jovian magnetosphere circulates magnetic field
>remarkably
>different from that of Earth
>
>
>For immediate release
>
>PIO Contact:
>Maria Martinez
>maria.martinez_at_swri.org
>(210) 522-3305
>
>
>San Antonio -- Oct. 23, 2007 -- Space physicists have long assumed that the
>magnetosphere at Jupiter circulates that planet's magnetic field in the
>same way as Earth. At Earth, this circulation drives the aurora and the
>magnetic storms that cause space weather. Researchers from Southwest
>Research Institute and the University of Colorado at Boulder have developed
>a new model that postulates the structure and magnetospheric processes at
>Jupiter are significantly different from those at Earth.
>
>
>
>The invisible area of space around a planet controlled by its magnetic
>field,
>the magnetosphere, interacts with the high-speed solar wind in a complex
>way,
>particularly in the area where the magnetic field in the solar wind
>interconnects with the planetary field, through a process called magnetic
>reconnection. The Dungey cycle, developed by British scientist Jim Dungey
>in 1961, is the scientifically accepted paradigm for explaining how
>magnetic
>reconnection circulates the Earth's magnetic field. During this cycle,
>magnetic
>field lines are brought up near the nose of the magnetosphere where they
>interconnect, becoming "open" and coupling the energy from the motion of
>the
>solar wind into the magnetosphere. That interconnection allows vast energy
>from the million mile-per-hour solar wind into the magnetosphere, which is
>the driving force behind geomagnetic storms, or space weather, that can
>seriously damage or destroy probes and satellites. Subsequent motion of the
>solar wind around the Earth's magnetosphere drags the interconnected field
>lines back over its magnetic poles where they drift down into the center of
>the magnetotail and reconnect again, but this time with similar field lines
>from the opposite hemisphere so that they are "closed" or connected to the
>planet at both ends. Finally, the Dungey cycle completes as the newly
>closed
>field lines circulate back toward Earth, around to its dayside and back to
>its starting position at the nose of the magnetosphere.
>
>"For years space physicists have considered the Dungey cycle to be the
>dominant circulation process in magnetospheres throughout the solar system,
>even though observations from the largest magnetosphere in the solar system
>--
>Jupiter's -- didn't add up," says Dr. David McComas, senior executive
>director
>of the Space Science and Engineering Division at Southwest Research
>Institute.
>
>"There are three key ways that the magnetosphere of Jupiter differs from
>that
>of Earth," argues Dr. Fran Bagenal, a professor of Astrophysical and
>Planetary
>Sciences at CU. "It's much bigger, it spins faster and it has a powerful
>source of material."
>
>The large size of the Jovian magnetosphere means that the time it takes for
>material that reconnects in the magnetotail and moves back up to Earth is
>only about 10 hours, less than half a day. However, the process at Jupiter
>takes 750 to 1,000 hours.
>
>"Consider that a Jupiter day is only about 10 hours," says McComas. "That
>means it would take as many as 100 Jovian days for reconnected field lines
>to
>move back up to Jupiter -- a staggering difference."
>
>Furthermore, the magnetosphere of Jupiter is coupled to the spinning
>planet.
>"Imagine stirring up a bowl of spaghetti," says Bagenal. "The fast, 10-hour
>spin of the Jovian magnetic field complicates the topology of flux tubes
>that are connected to the planet on one end while the other, open end is
>swept
>away by the solar wind."
>
>Another difference is that Jupiter has an active volcanic moon, Io, which
>spews out roughly a ton of material, mostly sulfur and oxygen, every
>second.
>Half of that material is lost through a process called charge exchange, but
>the other half moves down the Jovian magnetotail as ions dragging the
>planetary
>magnetic field tailward. Earth has no such counterpart to impede the
>return
>flow back toward the planet.
>
>The new theory suggests a different geometry for closing off the magnetic
>field
>that has become interconnected with the solar wind -- additional magnetic
>reconnection with other solar wind field lines that produce closed
>planetary
>field lines by reconnecting with open lines anchored back to both magnetic
>poles. This geometry at Jupiter allows for tailward flow everywhere in the
>tail and doesn't require a planetward flow, as at Earth. This explains why
>the
>polar aurora at Jupiter doesn't look like the terrestrial aurora. It also
>explains why observations from Ulysses showed that open flux occurs at low
>latitudes, not at the high latitudes required at Earth. The magnetosphere
>at
>Jupiter drags the material further down the sides so that they occur at
>lower
>latitudes.
>
>"Our model matches up with the observations -- further evidence that the
>magnetospheric structure and processes at Earth and Jupiter are quite
>different," says McComas.
>
>McComas and Bagenal determined these processes for Jupiter, yet they could
>aid
>in understanding the magnetospheres of the other outer planets, as well as
>in other astrophysical environments where magnetic fields play an important
>role.
>
>The paper, "Jupiter: A Fundamentally Different Magnetospheric Interaction
>with
>the Solar Wind," by David J. McComas and Fran Bagenal was published in the
>Oct. 24 issue of Geophysical Research Letters.
>
>
>Editors: Images to accompany this article are available at
>http://www.swri.org/press/2007/Jovian.htm.
>
>
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