Andrew Yee[_1_]
July 19th 07, 05:12 PM
Media Relations
Boston University
Contact:
Kira Jastive, 617-358-1240
For Release: July 18, 2007
BOSTON UNIVERSITY RESEARCHERS PRODUCE IMAGES OF GASES ESCAPING FROM
JUPITER'S MOON IO
Boston -- Boston University (BU) researchers published today the first clear
evidence of how gases from Jupiter's tiny moon's volcanoes can lead to the
largest visible gas cloud in the solar system. Jupiter, the largest planet
in the solar system, has a moon named Io that is just 100 km larger in
radius than Earth's Moon. According to lead researcher Michael Mendillo,
professor of electrical and computer engineering and astronomy at BU, there
are over 100 active volcanic sites on Io making it the most active place for
volcanic activity known anywhere.
"Of the various gases that come from Io's volcanoes, sodium atoms can be
detected using ground-based telescopes because the light they emit is in the
visible part of the spectrum -- the same familiar orange glow from sodium
street lights that are in most American cities," said Mendillo. "Therefore,
sodium atoms become a tracer of other elements that might be more abundant,
but less easy to see."
In 1990, BU scientists discovered a large gas cloud -- or nebula -- of
sodium atoms (Na) spanning great distances to either side of Jupiter.
"If this faint structure could be seen by the naked eye, it would be over
ten times the size of the full Moon, and thus the largest permanently
visible object in our solar system," Mendillo explained. "Computer models
suggested the types of escape processes needed to feed this giant nebula,
but actual pictures of those sources eluded observers for many years."
The research team from Boston University's College of Engineering and Center
for Space Physics (CSP) solved this problem by developing a novel way to
photograph these sources using a high-definition imaging (HDI) system that
combines several images into one clear picture.
The new images, published in the July 19th issue of the journal Nature,
reveal two distinct sources of sodium atoms escaping from Io. One is a
symmetrical cloud of escaping gas produced by collisions of the streaming
ions and electrons in Jupiter's so-called plasma torus. These plasma
particles are trapped in Jupiter's strong magnetic field and rotate with the
planet's 10-hour period, much faster than the 2-day orbital period of Io.
"So, there is a continuous plasma wind hitting Io, causing sodium atoms to
be sputtered from its atmosphere," Mendillo explained.
According to the scientists, this sputtering source is distinctly different
from a localized source of atoms produced chemically in the wake of the
streaming torus flow past Io. The images define the extent of the sputtering
and stream sources for the first time.
"Since the giant sodium nebula that they create varies over periods of
months to years, the source of the variability is probably not the
symmetrical sputtering cloud, but the streaming-wake source that waxes and
wanes with volcanic activity on Io," explained Jody Wilson, CSP senior
research associate and a study co-author.
The observations were made using a 4-meter telescope operated by the U.S.
Air Force on Maui, HI. To capture the faint signals from sodium atoms close
to Io, the observers had to find a way to cope with the bright sunlight
reflected from Io's surface, as well as from the even stronger light from
nearby Jupiter. In addition, ever-present turbulence in the Earth's
atmosphere causes the image of Io to jitter about randomly. Thus, any
attempt to capture the faint Na light by long time-exposures would result in
a highly blurred image.
"Our HDI system solved this problem in two ways. First, by taking very short
exposures -- 1/60th of a second -- the atmosphere might be steady for that
instant and thus occasional sharp images could be found; and second, by
dividing the full spectrum of light from Io into a narrow wavelength range,"
explained CSP senior research associate Jeffrey Baumgardner, the HDI
instrument designer and a co-author of the study. "That is, capturing only
the color needed to see sodium above the glare of full light and then using
most of the remaining light to simultaneously follow the fluctuating
positions of Io."
The goal was to then reposition Io to the same place in each frame and use
only the very clearest of those frames to make what Mendillo calls "the
ideal time exposure, one made with the target stationary, a good spectral
signal, and the best possible seeing."
The CSP observing team returned to Boston with 62,500 such images stored on
a computer and Mendillo wondering how the goal would be achieved. Study
co-author Sophie Laurent, a doctoral candidate at the time in Electrical and
Computer Engineering, assumed responsibility for the required signal
processing, with guidance from Professors Clem Karl and Janusz Konrad,
signal processing experts. Dr. Laurent devised automated ways to center all
of the images and then to find the highly-defined ones needed to make the
best possible images.
"These images provide specific spatial scales and relative strengths of
these sources that now can be put into computer models that attempt to
simulate how all types of gases escape from Io to populate the vast regions
of space surrounding Jupiter," Mendillo added.
This research was funded by the National Science Foundation (NSF) and the
Air Force Office of Scientific Research, and the HDI instrument by the
Office of Naval Research.
Founded in 1839, Boston University is an internationally recognized
institution of higher education and research. With more than 30,000
students, it is the fourth largest independent university in the United
States. It contains 17 colleges and schools along with a number of
multi-disciplinary centers and institutes which are central to the
university's research and teaching mission.
Boston University
Contact:
Kira Jastive, 617-358-1240
For Release: July 18, 2007
BOSTON UNIVERSITY RESEARCHERS PRODUCE IMAGES OF GASES ESCAPING FROM
JUPITER'S MOON IO
Boston -- Boston University (BU) researchers published today the first clear
evidence of how gases from Jupiter's tiny moon's volcanoes can lead to the
largest visible gas cloud in the solar system. Jupiter, the largest planet
in the solar system, has a moon named Io that is just 100 km larger in
radius than Earth's Moon. According to lead researcher Michael Mendillo,
professor of electrical and computer engineering and astronomy at BU, there
are over 100 active volcanic sites on Io making it the most active place for
volcanic activity known anywhere.
"Of the various gases that come from Io's volcanoes, sodium atoms can be
detected using ground-based telescopes because the light they emit is in the
visible part of the spectrum -- the same familiar orange glow from sodium
street lights that are in most American cities," said Mendillo. "Therefore,
sodium atoms become a tracer of other elements that might be more abundant,
but less easy to see."
In 1990, BU scientists discovered a large gas cloud -- or nebula -- of
sodium atoms (Na) spanning great distances to either side of Jupiter.
"If this faint structure could be seen by the naked eye, it would be over
ten times the size of the full Moon, and thus the largest permanently
visible object in our solar system," Mendillo explained. "Computer models
suggested the types of escape processes needed to feed this giant nebula,
but actual pictures of those sources eluded observers for many years."
The research team from Boston University's College of Engineering and Center
for Space Physics (CSP) solved this problem by developing a novel way to
photograph these sources using a high-definition imaging (HDI) system that
combines several images into one clear picture.
The new images, published in the July 19th issue of the journal Nature,
reveal two distinct sources of sodium atoms escaping from Io. One is a
symmetrical cloud of escaping gas produced by collisions of the streaming
ions and electrons in Jupiter's so-called plasma torus. These plasma
particles are trapped in Jupiter's strong magnetic field and rotate with the
planet's 10-hour period, much faster than the 2-day orbital period of Io.
"So, there is a continuous plasma wind hitting Io, causing sodium atoms to
be sputtered from its atmosphere," Mendillo explained.
According to the scientists, this sputtering source is distinctly different
from a localized source of atoms produced chemically in the wake of the
streaming torus flow past Io. The images define the extent of the sputtering
and stream sources for the first time.
"Since the giant sodium nebula that they create varies over periods of
months to years, the source of the variability is probably not the
symmetrical sputtering cloud, but the streaming-wake source that waxes and
wanes with volcanic activity on Io," explained Jody Wilson, CSP senior
research associate and a study co-author.
The observations were made using a 4-meter telescope operated by the U.S.
Air Force on Maui, HI. To capture the faint signals from sodium atoms close
to Io, the observers had to find a way to cope with the bright sunlight
reflected from Io's surface, as well as from the even stronger light from
nearby Jupiter. In addition, ever-present turbulence in the Earth's
atmosphere causes the image of Io to jitter about randomly. Thus, any
attempt to capture the faint Na light by long time-exposures would result in
a highly blurred image.
"Our HDI system solved this problem in two ways. First, by taking very short
exposures -- 1/60th of a second -- the atmosphere might be steady for that
instant and thus occasional sharp images could be found; and second, by
dividing the full spectrum of light from Io into a narrow wavelength range,"
explained CSP senior research associate Jeffrey Baumgardner, the HDI
instrument designer and a co-author of the study. "That is, capturing only
the color needed to see sodium above the glare of full light and then using
most of the remaining light to simultaneously follow the fluctuating
positions of Io."
The goal was to then reposition Io to the same place in each frame and use
only the very clearest of those frames to make what Mendillo calls "the
ideal time exposure, one made with the target stationary, a good spectral
signal, and the best possible seeing."
The CSP observing team returned to Boston with 62,500 such images stored on
a computer and Mendillo wondering how the goal would be achieved. Study
co-author Sophie Laurent, a doctoral candidate at the time in Electrical and
Computer Engineering, assumed responsibility for the required signal
processing, with guidance from Professors Clem Karl and Janusz Konrad,
signal processing experts. Dr. Laurent devised automated ways to center all
of the images and then to find the highly-defined ones needed to make the
best possible images.
"These images provide specific spatial scales and relative strengths of
these sources that now can be put into computer models that attempt to
simulate how all types of gases escape from Io to populate the vast regions
of space surrounding Jupiter," Mendillo added.
This research was funded by the National Science Foundation (NSF) and the
Air Force Office of Scientific Research, and the HDI instrument by the
Office of Naval Research.
Founded in 1839, Boston University is an internationally recognized
institution of higher education and research. With more than 30,000
students, it is the fourth largest independent university in the United
States. It contains 17 colleges and schools along with a number of
multi-disciplinary centers and institutes which are central to the
university's research and teaching mission.