HESSI
SPACECRAFT TO STEAL SECRETS OF SOLAR EXPLOSIONS WITH X-RAY VISION A
new NASA spacecraft will soon be studying gigantic explosions in the atmosphere
of the Sun with a unique kind of X-ray vision, producing the first high-fidelity
color movies of solar flares in their highest energy emissions. "The
Sun has a trick that nobody totally understands," said Dr. Richard Fisher,
Chief of the Laboratory for Astronomy and Solar Physics at NASA's Goddard Space
Flight Center, Greenbelt, MD. "It can take magnetic energy and turn it into
a stunningly powerful blast of heat, light and radiation. NASAs High Energy
Solar Spectroscopic Imager (HESSI) will finally unlock the secrets of the initiation
and onset of flares." Within
the gigantic flare explosions, magnetic fields twist, snap and recombine, blasting
particles to almost the speed of light and firing solar gas to tens of millions
of degrees. This action causes the solar atmosphere to sizzle with high-energy
X-rays and gamma rays and accelerates proton and electron particles into the solar
system. Radiation and particles from solar flares sometimes affect spacecraft,
interfering with communications, and astronaut activities. In
order to understand what triggers a solar flare and how it explosively releases
energy, scientists must identify the different kinds of particles being accelerated,
locate the regions where the acceleration occurs and determine when the particles
get accelerated. The most direct tracer of these accelerated particles is the
X-ray and gamma ray radiation they produce as they travel through the solar atmosphere. To
understand the physical processes and conditions inside flares, HESSI will create
images in gamma rays and the highest energy X-rays emitted by the flare. These
images will be the first to simultaneously measure the location and energy content
of radiation from the flare material. This kind of data is expected to improve
predictability of flare occurrence at the Sun and the subsequent consequences
we experience here on Earth. Using the Sun as a laboratory, where such high-energy
events take place, will provide scientists insight into interpreting similar high-energy
activity that originates elsewhere in the universe. Because
HESSI has the finest angular and spectral resolution of any hard X-ray or gamma
ray instrument ever flown in space, it will enable researchers for the first time
to look at the development of high-energy reactions in flares. Powerful X-rays
and gamma rays penetrate all materials to some extent, and cannot be easily focused,
so researchers are using another technique to form images. HESSIs sole instrument
an imaging spectrometer will construct a flare image from patterns
of light and shadows produced by high-energy radiation that passes through the
telescopes grids while the spacecraft rotates. Using this new method, HESSI
is expected to gather data on thousands of flares during its two-to-three-year
mission. Working
together with other solar spacecraft Yohkoh, the Solar and Heliospheric
Observatory (SOHO), Geostationary Operational Environmental Satellites (GOES),
and the Transitional Regional and Coronal Explorer (TRACE) for flare radiation,
and Wind, the Advanced Composition Explorer (ACE), Ulysses, and Voyager for particle
detection HESSI will provide vital insight into the impulsive energy release
and particle acceleration processes at the Sun. The
HESSI mission cost about $85 million, which includes the spacecraft, launch vehicle,
mission operations and data analysis. NASAs Office of Space Science in Washington,
DC oversees HESSI, and the Explorers Program Office at Goddard provides management
and technical oversight for the mission.
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