Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft

Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft

Courtesy of NASA

Solar flares happen on an 11-year cycle. They are giant explosions that take place on the Sun and have disruptive consequences on Earth and for vehicles traveling in space. Solar flares can release as much energy as a billion one-megaton nuclear bombs. Solar flares cannot be predicted and are not well understood because emissions happen at wavelengths that human eyes cannot detect. The equipment onboard RHESSI, a small explorer spacecraft orbiting above Earth’s atmosphere, is designed to make X-ray and spectroscopic images that humans can see. An additional benefit of studying solar flares is that they model high-energy explosions and particle acceleration happening at more distant places in the universe, which are not accessible.

February 2, 2002

February 2, 2002 (Earth orbit)

End of Mission
Still operating

RHESSI’s primary goal is to investigate the physics of particle acceleration and energy release in solar flares. To do this it will observe the processes that take place in the magnetized plasmas of the solar atmosphere during a flare: impulsive energy release, particle acceleration, and particle and energy transport.

RHESSI performed hard X-ray imaging spectroscopy and high-resolution spectroscopy of gamma-ray lines in solar flares. It obtained observations of at least a hundred X-ray flares and ten gamma-ray flares. However, it appears that some of these flares might have shuffled antimatter around, producing it in one location and destroying it in another. These observations provided insights into solar flares, which are the most powerful explosions in the solar system. RHESSI made the most detailed analysis to date of the gamma rays emitted when antimatter destroys ordinary matter in the solar atmosphere.

RHESSI was the first satellite to image solar gamma rays from a solar flare. RHESSI was the first satellite to accurately measure terrestrial gamma-ray flashes that come from thunder storms, and RHESSI found that such flashes occur more often than thought and the gamma rays have a higher frequency on average than the average for cosmic sources.