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Imagine the Universe News - 12 February 2002

Coming to a Theater Near You -- The Stormy Sun

12 February 2002

artist concept of HESSI

An artists conception of HESSI observing
the Sun from Earth orbit.

Lights, camera, action! With the launch of NASA's High Energy Solar Spectroscopic Imager, or HESSI, scientists will capture high-fidelity color movies of the most powerful events in the Solar System -- solar flares.

HESSI lifted off on February 5 from Cape Canaveral Air Force Station, Fla., tucked inside a Pegasus XL rocket and attached to the underbelly of the Orbital Stargazer L-1011 aircraft. The plane deployed the rocket at approximately 4:00 p.m. EST, and HESSI was soon on its way into space. During its planned two-year mission, HESSI will study the secrets of how solar flares are produced in the Sun's atmosphere.

Solar flares are violent eruptions on the surface of the Sun that occur when pent-up magnetic energy in the solar atmosphere is suddenly released. Intense radiation is emitted across virtually the entire electromagnetic spectrum, from radio waves through optical emission to x-rays and gamma rays. The amount of energy released is the equivalent of millions of 100-megaton hydrogen bombs exploding at the same time.

HESSI will study the X-ray and gamma-ray part of the solar flare. The satellite will determine the frequency, location, and evolution of impulsive energy release in the corona, or solar atmosphere. Imagine watching an explosion in slow motion. That's what HESSI will enable scientists to do. Even Hollywood can't come close to capturing such a fantastic event.

Specifically, HESSI will study the acceleration of electrons, protons, and heavier ions in flares; study the heating of plasma to tens of millions of degrees and determine its relationship to particle acceleration; study the propagation and evolution of energetic particles in flares; and determine the relative abundances of accelerated and ambient ions in flares.

Why study solar flares? They have a very direct connection to Earth. With each flare aimed towards our planet comes an influx of electrons and other particles. This can disrupt radio and cell phone communication on Earth, as well as cause damage to satellites. Because the light from a solar flare takes about 8 minutes to reach the Earth, though, we can get a head start in protecting sensitive electron equipment. Astronauts on the International Space Station also must seek temporary protection with each passing flare. (Particles travel more slowly than light, so electrons can arrive a day after a flare.)

Solar flares are interesting in a broader, scientific sense as well. Similar energy releases take place in other cosmic events, such as pulsars, black holes, and quasars. These events occur on objects that are too far away to study in the detail that solar flares can be studied on the Sun. So, scrutinizing "local" solar flares provides for a deeper understanding of these distant, exotic events.

Also, solar flares provide an opportunity to study physical processes in nature that are similar to those that occur in laboratory devices designed for the purpose of achieving controlled thermonuclear fusion.

HESSI scientists hope to capture hundreds of X-ray and gamma ray flares. Science operations should begin by March, after the germanium detectors inside the X-ray/gamma-ray imaging spectrometer are cooled to their operating temperature of -320 degrees Fahrenheit, turned on, and checked out.

In addition to observing the Sun, HESSI will also use its X-ray and gamma-ray instruments to observe pulsars, gamma-ray bursts, and X-ray binaries. During the summer, HESSI will also image the Crab Nebula at energies higher than those observed by Chandra.

HESSI is the first NASA Small Explorer mission managed in the "principal investigator" mode. Prof. Robert Lin of the University of California, Berkeley, is responsible for many aspects of the mission, including the science instrument, spacecraft integration and environmental testing, and spacecraft operations and data analysis.

The HESSI scientific payload is a collaborative effort between the University of California, Berkeley, NASA's Goddard Space Flight Center, the Paul Scherrer Institut in Switzerland, and the Lawrence Berkeley National Laboratory in Berkeley. The mission also involves scientific participation from France, Japan, The Netherlands, Scotland, and Switzerland.


A service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA/GSFC

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