RHESSI was a very valuable and ground-breaking mission. RHESSI first observed gamma rays from a solar eruption.

From Space Daily-

"High energies are always interesting in astronomy," University of Minnesota solar scientist Lindsay Glesener said. "They're the biggest explosions, the hottest plasma. But flares are going on at our Sun, which is right next to us and affects us in lots of ways. When I was a grad student, it took just one conversation with Robert Lin, the principal investigator from 2002 to 2012, to convince me flares are the most fascinating thing in the universe." (snip)

"RHESSI had several firsts," Dennis said. "No one had ever imaged X-rays at this high an energy level before, or imaged gamma rays at all. RHESSI made great strides by making energy measurements with higher resolution than had previously been possible."

Solar Flares Aren't Simple

Early RHESSI observations of a strong flare on April 15, 2002, showed X-rays coming from two different places at once: one high in the Sun's atmosphere and another lower down. Researchers interpreted this to mean a huge punch of energy occurred between the two spots.

After tracking the energy in the two-sided explosion, they realized part of the explosion's energy shot high into the Sun's atmosphere and burst into a cloud of hot plasma to become a coronal mass ejection, while the other part bore down towards the surface, exploding into a flare.

These explosions - the most powerful in the solar system - came to be known as solar eruptive events, in which the Sun's strongest flares and coronal mass ejections are linked, occurring at the same time.

RHESSI introduced solar researchers to entirely new questions on the nature of flares. During an intense October 2003 flare, scientists noticed X-rays and gamma rays coming from two different places.

Although electrons and ions have different masses, scientists expected them to originate from the same spot in the flare. Since each kind of emission reflects the presence of different kinds of particles, the unexpected disparity hinted at different mechanisms guiding the movements of each type of particle. Scientists still don't fully understand this process.

Much more here:
[link to www.spacedaily.com]

Movie clip of Jan 20, 2005 X-flare:

[link to www.scholarpedia.org]

RHESSI NASA Mission Homepage w/ links to archived data:

[link to hesperia.gsfc.nasa.gov (secure)]

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