[FPSPACE] Voyager 2: Sol system termination shock boundary is "squashed"
ljk4 at msn.com
Mon Dec 10 10:44:35 EST 2007
VOYAGER 2 PROVES SOLAR SYSTEM IS SQUASHED
San Francisco, Calif. - NASA's Voyager 2 spacecraft has followed its twin
Voyager 1 into the solar system's final frontier, a vast region at the edge
of our solar system where the solar wind runs up against the thin gas
between the stars.
However, Voyager 2 took a different path, entering this region, called the
heliosheath, on August 30, 2007. Because Voyager 2 crossed the heliosheath
boundary, called the solar wind termination shock, about 10 billion miles
away from Voyager 1 and almost a billion miles closer to the sun, it
confirmed that our solar system is squashed or dented that the bubble
carved into interstellar space by the solar wind is not perfectly round.
Where Voyager 2 made its crossing, the bubble is pushed in closer to the sun
by the local interstellar magnetic field.
Voyager 2 continues its journey of discovery, crossing the termination
shock multiple times as it entered the outermost layer of the giant
heliospheric bubble surrounding the Sun and joined Voyager 1 in the last leg
of the race to interstellar space. said Voyager Project Scientist Dr.
Edward Stone of the California Institute of Technology, Pasadena, Calif.
The solar wind is a thin gas of electrically charged particles (plasma)
blown into space by the sun. The solar wind blows in all directions, carving
a bubble into interstellar space that extends past the orbit of Pluto. This
bubble is called the heliosphere, and Voyager 1 was the first spacecraft to
explore its outer layer, when it crossed into the heliosheath in December
2004. As Voyager 1 made this historic passage, it encountered the shock wave
that surrounds our solar system called the solar wind termination shock,
where the solar wind is abruptly slowed by pressure from the gas and
magnetic field in interstellar space.
Even though Voyager 2 is the second spacecraft to cross the shock, it is
scientifically exciting for a couple of reasons. The Voyager 2 spacecraft
has a working Plasma Science instrument that can directly measure the
velocity, density and temperature of the solar wind. This instrument is no
longer working on Voyager 1 and estimates of the solar wind speed had to be
made indirectly. Secondly, Voyager 1 may have had only a single shock
crossing and it happened during a data gap. But Voyager 2 had at least five
shock crossings over a couple of days (the shock sloshes back and forth
like surf on a beach, allowing multiple crossings) and three of them are
clearly in the data. They show us an unusual shock.
In a normal shock wave, fast-moving material slows down and forms a denser,
hotter region as it encounters an obstacle. However, Voyager 2 found a much
lower temperature beyond the shock than was predicted. This probably
indicates that the energy is being transferred to cosmic ray particles that
were accelerated to high speeds at the shock.
"The important new data describing the termination shock are still being
pondered, but it is clear that Voyager has once again surprised us," said
Dr. Eric Christian, Voyager Program Scientist at NASA Headquarters,
The two Voyager spacecraft will be the only source of local observations of
this distant but highly interesting region for years to come. But in the
summer of 2008, NASA will be launching a mission specifically designed to
globally image the termination shock and heliosheath remotely from Earth
orbit. The Interstellar Boundary Explorer (IBEX), led by Dr. David McComas
of the Southwest Research Institute in San Antonio, Texas, will use
energetic neutral atoms (ENAs) to create all-sky maps at various energies of
the interaction of the heliosphere with interstellar space. ENAs are formed
when energetic electrically-charged particles steal an electron from
another particle. Once neutral, they travel straight, unaffected by the
solar magnetic field. IBEX will detect some of the particles that happen to
be headed towards the Earth, and the number and energy of the particles
coming from all different directions will tell us much more about the
overall structure of the interaction between the heliosphere and
Results on the Voyager 2 shock crossing from the entire Voyager science team
are being presented at the Fall 2007 meeting of the American Geophysical
Union in San Francisco. The Voyagers were built by NASAs Jet Propulsion
Laboratory (JPL) in Pasadena, Calif., which continues to operate both
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