Andrew Yee[_1_]
July 3rd 08, 02:16 AM
Media Relations
University of California-Berkeley
Media Contacts:
Robert Sanders
(510) 643-6998, (510) 642-3734
2 July 2008
First images of solar system's invisible frontier
By Robert Sanders, Media Relations
BERKELEY -- NASA's sun-focused STEREO spacecraft unexpectedly detected
particles from the edge of the solar system last year, allowing University
of California, Berkeley, scientists to map for the first time the energized
particles in the region where the hot solar wind slams into the cold
interstellar medium.
Mapping the region by means of neutral, or uncharged, atoms instead of light
"heralds a new kind of astronomy using neutral atoms," said Robert Lin, UC
Berkeley professor of physics and lead for the suprathermal electron sensor
aboard STEREO. "You can't get a global picture of this region, one of the
last unexplored regions of the heliosphere, any other way because it is too
tenuous to be seen by normal optical telescopes."
The heliosphere is a volume over which the effects of the solar wind extend,
stretching from the sun to more than twice the distance of Pluto. Beyond its
edge, called the heliopause, lies the relative quiet of interstellar space,
at about 100 astronomical units (AU) -- 100 times the Earth-sun distance.
The results, reported in the July 3 issue of the journal Nature, clear up a
discrepancy in the amount of energy dumped into space by the decelerating
solar wind that was discovered last year when Voyager 2 crossed the solar
system's termination shock and entered the surrounding heliosheath. The
termination shock is the region of the heliosphere where the supersonic
solar wind slows to subsonic speed as it merges with the interstellar
medium. The heliosheath is the region of roiled plasma between the shock
front and the interstellar medium.
The newly discovered population of ions in the heliosheath contains about 70
percent of the energy dissipated in the termination shock, exactly the
amount unaccounted for by Voyager 2's instruments, the UC Berkeley
physicists concluded. The Voyager 2 results are reported in the same issue
of Nature.
The twin STEREO spacecraft were launched in 2006 into Earth's orbit about
the sun to obtain stereo pictures of the sun's surface and to measure
magnetic fields and ion fluxes associated with solar explosions.
Between June and October 2007, however, the suprathermal electron sensor in
the IMPACT (In-situ Measurements of Particles and CME Transients) suite of
instruments on board each STEREO spacecraft detected neutral atoms
originating from the same spot in the sky: the shock front and the
heliosheath beyond, where the sun plunges through the interstellar medium.
"The suprathermal electron sensors were designed to detect charged
electrons, which fluctuate in intensity depending on the magnetic field,"
said lead author Linghua Wang, a graduate student in UC Berkeley's
Department of Physics. "We were surprised that these particle intensities
didn't depend on the magnetic field, which meant they must be neutral
atoms."
UC Berkeley physicists concluded that these energetic neutral atoms were
originally ions heated up in the termination that lost their charge to cold
atoms in the interstellar medium and, no longer hindered by magnetic fields,
flowed back toward the sun and into the suprathermal electron sensors on
STEREO.
"This is the first mapping of energetic neutral particles from beyond the
heliosphere," Lin said. "These neutral atoms tell us about the hot ions in
the heliosheath. The ions heated in the termination shock exchange charge
with the cold, neutral atoms in the interstellar medium to become neutral,
and then flow back in."
According to Lin, the neutral atoms are probably hydrogen, since most of the
particles in the local interstellar medium are hydrogen.
The charge exchange between hot ions and neutral atoms to generate energetic
neutral atoms is well known around the sun and planets, including Earth and
Jupiter, and has been used by spacecraft such as IMAGE and Cassini as a
means of remotely measuring the energy in ion plasmas, since neutral atoms
travel much farther than ions. A new NASA mission, the Interstellar Boundary
Explorer (IBEX), is planned for launch later this year to map more
thoroughly the lower-energy energetic ions in the heliosheath by means of
energetic neutral atoms to discover the structure of the termination shock
and how hydrogen ions are accelerated there.
Lin and Wang's coauthors are IMPACT principal investigator Janet G. Luhmann
and researcher Davin E. Larson. All are affiliated with UC Berkeley's Space
Sciences Laboratory, which Lin directs.
IMAGE CAPTION:
[http://www.berkeley.edu/news/media/releases/2008/07/images/helio.png (9KB)]
STEREO detected energetic neutral atoms (ENAs) from the edge of the solar
system, where the solar wind meets the interstellar medium. These ENAs were
traced back to hot ions in the heliosheath -- the region between the
termination shock and heliopause -- which are more intense (indicated by
color code) around the nose of the heliosphere, with an asymmetric double
peak. The twin STEREO A and B spacecraft are shown in the sun-centered orbit
they share with Earth. Last year, the Voyager 2 spacecraft passed into the
heliosheath, joining Voyager 1. There, these interstellar explorers continue
their journey into the farthest reaches of the heliosphere. (Linghua Wang/UC
Berkeley)
University of California-Berkeley
Media Contacts:
Robert Sanders
(510) 643-6998, (510) 642-3734
2 July 2008
First images of solar system's invisible frontier
By Robert Sanders, Media Relations
BERKELEY -- NASA's sun-focused STEREO spacecraft unexpectedly detected
particles from the edge of the solar system last year, allowing University
of California, Berkeley, scientists to map for the first time the energized
particles in the region where the hot solar wind slams into the cold
interstellar medium.
Mapping the region by means of neutral, or uncharged, atoms instead of light
"heralds a new kind of astronomy using neutral atoms," said Robert Lin, UC
Berkeley professor of physics and lead for the suprathermal electron sensor
aboard STEREO. "You can't get a global picture of this region, one of the
last unexplored regions of the heliosphere, any other way because it is too
tenuous to be seen by normal optical telescopes."
The heliosphere is a volume over which the effects of the solar wind extend,
stretching from the sun to more than twice the distance of Pluto. Beyond its
edge, called the heliopause, lies the relative quiet of interstellar space,
at about 100 astronomical units (AU) -- 100 times the Earth-sun distance.
The results, reported in the July 3 issue of the journal Nature, clear up a
discrepancy in the amount of energy dumped into space by the decelerating
solar wind that was discovered last year when Voyager 2 crossed the solar
system's termination shock and entered the surrounding heliosheath. The
termination shock is the region of the heliosphere where the supersonic
solar wind slows to subsonic speed as it merges with the interstellar
medium. The heliosheath is the region of roiled plasma between the shock
front and the interstellar medium.
The newly discovered population of ions in the heliosheath contains about 70
percent of the energy dissipated in the termination shock, exactly the
amount unaccounted for by Voyager 2's instruments, the UC Berkeley
physicists concluded. The Voyager 2 results are reported in the same issue
of Nature.
The twin STEREO spacecraft were launched in 2006 into Earth's orbit about
the sun to obtain stereo pictures of the sun's surface and to measure
magnetic fields and ion fluxes associated with solar explosions.
Between June and October 2007, however, the suprathermal electron sensor in
the IMPACT (In-situ Measurements of Particles and CME Transients) suite of
instruments on board each STEREO spacecraft detected neutral atoms
originating from the same spot in the sky: the shock front and the
heliosheath beyond, where the sun plunges through the interstellar medium.
"The suprathermal electron sensors were designed to detect charged
electrons, which fluctuate in intensity depending on the magnetic field,"
said lead author Linghua Wang, a graduate student in UC Berkeley's
Department of Physics. "We were surprised that these particle intensities
didn't depend on the magnetic field, which meant they must be neutral
atoms."
UC Berkeley physicists concluded that these energetic neutral atoms were
originally ions heated up in the termination that lost their charge to cold
atoms in the interstellar medium and, no longer hindered by magnetic fields,
flowed back toward the sun and into the suprathermal electron sensors on
STEREO.
"This is the first mapping of energetic neutral particles from beyond the
heliosphere," Lin said. "These neutral atoms tell us about the hot ions in
the heliosheath. The ions heated in the termination shock exchange charge
with the cold, neutral atoms in the interstellar medium to become neutral,
and then flow back in."
According to Lin, the neutral atoms are probably hydrogen, since most of the
particles in the local interstellar medium are hydrogen.
The charge exchange between hot ions and neutral atoms to generate energetic
neutral atoms is well known around the sun and planets, including Earth and
Jupiter, and has been used by spacecraft such as IMAGE and Cassini as a
means of remotely measuring the energy in ion plasmas, since neutral atoms
travel much farther than ions. A new NASA mission, the Interstellar Boundary
Explorer (IBEX), is planned for launch later this year to map more
thoroughly the lower-energy energetic ions in the heliosheath by means of
energetic neutral atoms to discover the structure of the termination shock
and how hydrogen ions are accelerated there.
Lin and Wang's coauthors are IMPACT principal investigator Janet G. Luhmann
and researcher Davin E. Larson. All are affiliated with UC Berkeley's Space
Sciences Laboratory, which Lin directs.
IMAGE CAPTION:
[http://www.berkeley.edu/news/media/releases/2008/07/images/helio.png (9KB)]
STEREO detected energetic neutral atoms (ENAs) from the edge of the solar
system, where the solar wind meets the interstellar medium. These ENAs were
traced back to hot ions in the heliosheath -- the region between the
termination shock and heliopause -- which are more intense (indicated by
color code) around the nose of the heliosphere, with an asymmetric double
peak. The twin STEREO A and B spacecraft are shown in the sun-centered orbit
they share with Earth. Last year, the Voyager 2 spacecraft passed into the
heliosheath, joining Voyager 1. There, these interstellar explorers continue
their journey into the farthest reaches of the heliosphere. (Linghua Wang/UC
Berkeley)