From: LARRY KLAES (ljk4_at_msn.com)
Date: Wed Jan 01 2003 - 20:12:56 PST
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From: Ron Baalke
Sent: Wednesday, January 01, 2003 10:22 PM
To: ljk4_at_msn.com
Subject: Volcanoes On Jovian Moon Io Spew Salt Into Atmosphere
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Johns Hopkins University
Contact: Michael Purdy
mcp_at_jhu.edu
410-516-7160
Volcanoes on Jovian moon spew salt into atmosphere
Discovery explains 1970s observation of sodium above Io
January 1, 2003
Astronomers at The Johns Hopkins University, the Observatoire de Paris, and
other institutions have solved a nearly 30-year-old mystery surrounding
Jupiter's moon Io, showing that volcanoes there appear to be shooting
gaseous salt into the moon's thin atmosphere.
"This gives nice closure to the discovery Bob Brown made in 1974 of sodium
in neutral clouds of gas around Io, " said Darrell Strobel, a professor of
earth and planetary sciences in the Krieger School of Arts and Sciences at
Johns Hopkins and an author of a paper on the new results in the Jan. 2
issue of "Nature."
Further analysis of the results, including modeling how the salt is broken
down into sodium and chlorine atoms, could help planetary scientists move
closer to determining what kinds of meteoritic materials originally came
together to form Io, according to Strobel.
Strobel said Brown, who later became a project scientist at the Space
Telescope Science Institute, found the sodium around Io while testing out a
spectrograph he had built.
"He told me some years afterwards, 'This discovery of mine is so simple. I
was amazed somebody hadn't done it 30 to 40 years earlier,'" Strobel said.
"Nobody was looking for it; nobody would have guessed it was there."
Astronomers winnowed the list of theoretical suspects for the source of
sodium for years before determining the most likely suspect was salt, or
sodium chloride. That conclusion was reached after the detection two years
ago of chlorine in a doughnut-shaped, electrically charged cloud of gas
around Io known as the plasma torus. Based on the new chlorine finding and
the theoretical work, astronomers decided to conduct the exacting studies
necessary to look for salt.
"The bottom line is that there seems to be enough salt in Io's volcanic
atmosphere to supply both the amount of sodium that one sees in the neutral
clouds and the chlorine in the plasma torus," said Strobel, who is also a
professor of physics and astronomy at Johns Hopkins.
A slightly eccentric orbit around Jupiter and the gravitational fields of
two nearby large moons, Europa and Ganymede, subject Io to a great deal of
stress, flexing the moon's crust and heating its core. As a result, Io is
hands-down the most volcanically active planetary body in the solar system.
Roughly comparable in size to Earth's moon, Io's frequently active volcanoes
would make it a hell for anyone who might want to visit, but it's a heaven
for scientists eager to watch a planetary body regularly belch up tons of
its innards.
"Roughly two tons of volcanic material are tossed into Io's magnetosphere
every second, and then when this material is ionized [electrically charged],
the inner magnetosphere starts to resemble a miniature pulsar," Strobel
said.
Interactions between the clouds of electrically charged gas around Io and
electrically charged particles in Jupiter's polar atmosphere speed up the
rotation of the charged particles around Io but also apply an infinitesmal
drag to the rotation of Jupiter, gradually slowing the speed at which the
giant planet spins.
"It's a remarkable, unique system of interaction," Strobel said. "We've
learned quite a bit since the days when Voyager 1 first swept by the moon in
1979 and revealed eight active volcanoes, but we don't understand it
completely."
Strobel said the lead author of the new "Nature" paper, Emmanuel Lellouch of
the Observatoire de Paris, had looked previously for salt in Io's atmosphere
and failed to find signs of it. Co-author Nicholas Snyder of the University
of Colorado at Boulder, one of the researchers who discovered chlorine in
Io's plasma torus, suggested using millimeter-wavelength radio telescope at
the Institut de Radio-Astronomie Millimetrique in Granada, Spain, to perform
a definitive search for salt.
Observations with a millimeter-wavelength radio telescope force astronomers
to focus on very tiny regions of the spectrum, making it necessary to
carefully choose the frequencies they want to observe. But when the team
conducted its studies in January 2002, they found the characteristic
spectroscopic lines they were looking for. An examination of potential
sources for the salt in the atmosphere pointed to the volcanoes as the most
likely point of origin for the salt.
###
Other authors on the paper were Gabriel Paubert of the Institut de
Radio-Astronomie Millimetrique; and Julianne Moses of NASA's Lunar and
Planetary Institute. This research was supported by the NASA Planetary
Atmospheres Program.
Related Web sites:
Darrell Strobel: http://www.jhu.edu/~eps/faculty/strobel/index.html
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