Solar flares erupting on the Sun's surface are the most massive explosions in our Solar System, which makes them hot beyond all reason. But a young NASA observatory trained on the Earth's parent star found the flares even hotter than researchers originally thought, and should bolster their understanding of the stellar phenomenon. It could one day even help scientists predict when solar flares occur.

"This is a years-long effort, but the potential is there," said solar physicist Gordon Emslie, who led the recent solar flare study. "It's our ability to interpret the data that will tell."

Emslie, of the University of Alabama in Huntsville (UAH), used the young Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) to study a single solar flare with unprecedented detail.

Solar physicists have long known that flares were a hot topic. The largest ones can explode with a force equivalent to about 10 million megatons, where one megaton is about the destructive power of a hydrogen bomb.

But Emslie's team found that the solar eruptions can reach up to 80 million degrees Fahrenheit (almost 45 million degrees Celsius), a jump of up about 10 million degrees from previous estimates, researchers said.

The satellite was renamed RHESSI after the late NASA scientist Reuven Ramaty, who pioneered the fields of solar-flare physics, gamma-ray astronomy and cosmic ray research. Ramaty, died in 2001 of Lou Gehrig's disease after a long, distinguished career in the Laboratory for High Energy Astrophysics at the NASA Goddard Space Flight Center in Greenbelt, Md.

RHESSI recorded images of a solar flare that erupted on July 23, 2002. The observations show a bright blob of illumination within the hot flare itself, suggesting even higher temperatures from high-energy particles.

"About one-fifth of the entire heat emission came from this one blob," Emslie told SPACE.com.

RHESSI scientists said the July 2002 flare is probably not going to be the hottest one ever detected, but it does indicate that solar flares can be dissected to find specific areas of higher energy release. "That's important because if we can understand the environment of a solar flare then we're one step closer to understanding why they occur," Emslie explained.

A better grasp of solar flares is useful because they play a large part in space weather, which can adversely effect global communications should a flare erupt on an Earth-facing portion of the Sun. More than that, flares can sometimes be associated with coronal mass ejections, where bubbles the Sun's gases shoot out of the star over a period of hours.

"We have seen these coronal mass ejections occur close to large solar flares," said Robert Lin of UC Berkeley. Lin is the principal investigator for RHESSI. "But we still don't understand how all this energy is released."

Lin told SPACE.com that much of a solar flare's energy stems from its high-energy particles, which it pushes like a natural particle accelerator. As the particles stream away from the Sun they slam into the star's atmosphere, producing the X-rays and gamma rays RHESSI sees. By observing how these particles act as they leave the Sun, researchers can determine the physical processes accelerating them into space and formulate better ideas about the roots of solar flares.

"One of the applications we're clearly aiming towards is try and understand flares well enough that we can predict them," said Lin, conceding that the goal was a long way off. "We're at about as far with flare prediction as scientists were with in predicting the weather around World War II."

RHESSI researchers said it could also be possible to adopt what they learn about the Sun's natural particle accelerator processes to the movements of particles near black holes, active galactic nuclei and even manmade atom smashers on Earth.

"The great thing is we don't have to look too hard for particle acceleration around a black hole when the Sun is next door," Emslie said. "From an astrophysical standpoint, the Sun is our laboratory."

But the RHESSI team has some time. Since its launch last year, RHEESI has continuously watched the Sun for signs of solar flares and it seems like the best may be yet to come.

The Sun's solar activity runs on an 11-year cycle that moves from minimum to maximum and back again over the course. RHEESI launched about a year too late to catch the bulk of solar maximum, a period where flares, coronal mass ejections and sunspots are at their peak.

"The main limitation is the Sun itself, which is nearing the end of its solar maximum [period]," said Emslie. "But the good news is that the largest flares tend to occur during this time."