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Solar
flare satellite orbits into second month in space, gets new
name: RHESSI
28
March 2002
By Robert
Sanders, Media Relations
Video
of Feb. 20 solar flare
Berkeley
– Nearly two months after the Feb. 5 launch of NASA's solar
flare satellite, HESSI, the University of California, Berkeley,
scientists who designed and build it couldn't be happier. The
satellite is working flawlessly and has already captured numerous
explosive flares as well as X-ray and gamma ray flashes from
elsewhere in the cosmos.
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An
X-ray snapshot of a solar flare, colored to indicates the
energy of the X-rays. Blue is the most energetic and red
is the least energetic. Presumably, Lin said, the blue spots
indicate that the more energetic electrons are able to travel
deeper into the solar atmosphere, down to footpoints of
the magnetic loop, while the less energetic electrons, perhaps
a hot thermal source, may be trapped higher in the loop.
Photo, UC Berkeley & NASA Goddard |
"It's
absolutely beautiful," said Robert Lin, principal investigator
for the HESSI mission and professor of physics. "We have seen
some really neat stuff."
Lin also
is pleased that the satellite has been rechristened RHESSI –
the Reuven Ramaty High-Energy Solar Spectroscopic Imager –
in honor of the late NASA scientist who pioneered the fields
of solar-flare physics, gamma-ray astronomy and cosmic ray research.
Ramaty died last year of Lou Gehrig's disease after a long and
distinguished career in the Laboratory for High Energy Astrophysics
at the NASA Goddard Space Flight Center in Greenbelt, Md.
"He was
one of the people who pushed real hard to get HESSI funded,"
said Lin, who proposed to NASA that it change the satellite's
name to honor Ramaty. "He was really looking forward to HESSI's
launch, but he passed away before the spacecraft went up. It's
appropriate that we name it after him."
RHESSI
to date has imaged more than 50 small and medium X-ray flares,
though so far no large solar flares emitting gamma rays. Flares
are among the most powerful events on the Sun, and can occasionally
disrupt satellites, communication systems and power grids on
Earth. Scientists believe solar flares are powered by the violent
release of magnetic energy, but how this happens is a mystery.
"Their
behavior is really amazing, much more complicated than people
guessed beforehand," Lin said. "They will take a while to analyze."
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Video:
this movie records the X-ray and gamma radiation
released by a solar flare, energy equivalent to one million
megatons of TNT
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NASA
created a movie of one of the flares superimposed on solar images
from the SOHO satellite (Solar & Heliospheric Observatory)
and the ground-based Big Bear Solar Observatory in California.
This was an explosion Feb. 20 in the atmosphere on the southern
hemisphere of the Sun, in an active region designated AR 9830.
The blast was equal to one million megatons of TNT and gave
off powerful bursts of X-rays.
"We are
thrilled to be making the first high-resolution movies of flares
using their high-energy radiation," said Brian Dennis, the RHESSI
mission scientist at Goddard. "We want to understand how solar
flares can explosively release so much energy. RHESSI shows
us the high-energy radiation emitted by flares: their X-rays
and gamma rays. This radiation reveals the core of the flare
– the exact time and place where the energy is released."
RHESSI
also has seen several non-solar events, including a soft gamma
ray burster and X-rays that may be from the black hole binary
Cygnus X-1. These X-rays and gamma rays penetrated the sides
of the spacecraft and hit the detectors, so they couldn't be
turned into an image. But because RHESSI has the best energy
resolution for such high-energy radiation of any satellite,
Lin hopes the instruments can provide unique information on
these and other X-ray and gamma ray sources by searching for
emission and absorption lines and obtaining Doppler shifts indicative
of chemical composition and motions, respectively. RHESSI also
can study X-ray pulsars, which are stars that flash at regular
intervals.
The immediate
goal of the UC Berkeley RHESSI team, however, is to switch the
spacecraft over to automatic operation, so that the operations
team doesn't have to scramble every time the satellite passes
over Berkeley and downloads data, often in the middle of the
night. Lin is hopeful this will be achieved in early April.
During
its planned two-year mission, RHESSI will study the secrets
of how solar flares are produced in the Sun's atmosphere. RHESSI
is the first NASA Small Explorer mission managed in the "principal
investigator" mode, where Lin and his team are responsible for
most aspects of the mission, including the science instrument,
spacecraft integration and environmental testing, and spacecraft
operations and data analysis. The RHESSI
scientific payload is a collaborative effort among UC Berkeley;
Goddard, the Paul Scherrer Institut in Switzerland and the Lawrence
Berkeley National Laboratory. The mission also involves additional
scientific participation from France, Japan, The Netherlands,
Scotland and Switzerland. |
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