THEMIS Weighs In On The Northern Lights (Forwarded)

Communications Department
Lawrence Berkeley National Laboratory

Contact:
Paul Preuss, (510) 486-6249

March 14, 2007

THEMIS Weighs In On The Northern Lights

Berkeley Lab Detectors Gather Data on Earth's Auroras, Radiation Belts, and
the Solar Wind

BERKELEY, CA -- Instruments known as solid-state telescopes (SSTs), built
with detectors fabricated at Lawrence Berkeley National Laboratory and
carried aboard the recently launched THEMIS mission, have delivered their
first data on how charged particles in the solar wind interact with Earth's
magnetic field to shape the planet's magnetosphere.

THEMIS's principal investigator is Vassilis Angelopoulos of the University
of California at Berkeley's Space Sciences Laboratory (SSL), which is
leading the mission for NASA and which designed and built the instruments in
collaboration with agencies in Germany, France, and Austria.

The first NASA mission comprised of five different coordinated spacecraft,
all five THEMIS spacecraft were launched from Cape Canaveral together aboard
a single rocket on February 17, 2007. Eventually the five will study the
mysterious eruptions in Earth's Northern and Southern Lights known as
"substorms," but first they must achieve widely separated orbits, a process
that will take several months.

An acronym for Time History of Events and Macroscopic Interactions during
Substorms, THEMIS will obtain the evidence needed to solve what principal
investigator Angelopoulos calls "a nagging question that the field has to
resolve" -- namely, competing theories about where auroral substorms
originate in the magnetosphere.

As one of several instrument systems carried aboard the five THEMIS
spacecraft, the solid-state telescopes will gather some of the most
important evidence. The SST's job is to measure the energy distribution of
electrons and ions (charged atoms and atomic nuclei) arriving at each
spacecraft from different parts of the sky. To do this, the SSTs use
custom-built silicon diode detectors made in Berkeley Lab's Microsystems
Laboratory by Craig Tindall, Steve Holland, and Nick Palaio of the
Engineering Division.

These large-area detectors have very thin contacts, only a few hundred
angstroms thick. This allows them to detect electrons and ions with energies
much lower than those that can be detected with standard silicon detectors,
giving the SSTs the ability to cover a wide energy range, from high to low.
But because the contacts are so thin, making a sufficient quantity of the
large detectors posed a significant challenge.

Says Tindall, "Berkeley Lab's Microsystems Laboratory provided advanced
equipment and processes in an ultraclean environment, enabling the
fabrication of these detectors with high yield."

Using the finished detectors, UC Berkeley's Davin Larson directed assembly
of the solid-state telescopes at SSL. Each SST is based on four detectors;
two SSTs mounted side by side and pointing in opposite directions form a
unit, and two units are mounted on each spacecraft, for a total of 80
silicon diode detectors flown aboard the five spacecraft.

Berkeley Lab has a long history of creating and fabricating innovative
detectors, beginning with detectors for high-energy particle experiments in
accelerators and recently including detectors for space missions like
STEREO, NASA's twin Solar Terrestrial Relations Observatories, launched in
2006; the Spitzer Space Telescope, launched in 2004; and RHESSI, the Ramaty
High Energy Solar Spectroscopic Imager, launched in 2002.

Tindall and Palaio made detectors for the IMPACT instrument suite aboard
STEREO using the same process as the THEMIS detectors; these are currently
returning data on energetic solar particles.

THEMIS is managed by NASA's Goddard Spaceflight Center Explorers office. For
more information about auroras, the magnetosphere, and the scientific and
technical aspects of THEMIS, visit SSL's site at
http://themis.ssl.berkeley.edu/
and NASA's site at
http://www.nasa.gov/mission_pages/th...ain/index.html

Berkeley Lab is a U.S. Department of Energy national laboratory located in
Berkeley, California. It conducts unclassified scientific research and is
managed by the University of California. Visit our website at
http://www.lbl.gov

IMAGE CAPTIONS:

[Image 1:
http://www.lbl.gov/Science-Articles/...EMIS_fleet.jpg
(30KB)]
THEMIS consists of five spacecraft, studying the conditions in Earth's
magnetosphere that spark disturbances in the auroras.

[Image 2:
http://www.lbl.gov/Science-Articles/...spacecraft.jpg
(30KB)]
One of the five THEMIS spacecraft prior to launch. Its two solid-state
telescope units, each with two opposite-facing SSTs incorporating four
silicon detectors each, are mounted on the near edge.