Solar flare surprise

December 15, 2008,

The X9-class solar flare of Dec. 5, 2006, observed by the Solar X-Ray Imager aboard NOAA's GOES-13 satellite. Credit: NOAA's Space Weather Prediction Center
(PhysOrg.com) -- Solar flares are the most powerful explosions in the solar system. Packing a punch equal to a hundred million hydrogen bombs, they obliterate everything in their immediate vicinity. Not a single atom should remain intact. At least that's how it's supposed to work.

"We've detected a stream of perfectly intact hydrogen atoms shooting out of an X-class solar flare," says Richard Mewaldt of the California Institute of Technology. "What a surprise! If we can understand how these atoms were produced, we'll be that much closer to understanding solar flares."

The event occurred on Dec. 5, 2006. A large sunspot rounded the sun's eastern limb and with little warning it exploded. On the "Richter scale" of flares, which ranks X1 as a big event, the blast registered X9, making it one of the strongest flares of the past 30 years.

NASA managers braced themselves. Such a ferocious blast usually produces a blizzard of high-energy particles dangerous to both satellites and astronauts. An hour later they arrived, but they were not the particles researchers expected.

NASA's twin Solar TErrestrial RElations Observatory (STEREO) spacecraft made the discovery: "It was a burst of hydrogen atoms," says Mewaldt. "No other elements were present, not even helium (the sun's second most abundant atomic species). Pure hydrogen streamed past the spacecraft for a full 90 minutes."

Next came 30 minutes of quiet. The burst subsided and STEREO's particle counters returned to low levels. The event seemed to be over when a second wave of particles enveloped the spacecraft. These were the "broken atoms" flares are supposed to produce—protons and heavier ions such as helium, oxygen and iron. "Better late than never," he says.

At first, this unprecedented sequence of events baffled scientists, but now Mewaldt and colleagues believe they're getting to the bottom of the mystery.

First, how did the hydrogen atoms resist destruction?

"They didn't," says Mewaldt. "We believe they began their journey to Earth in pieces, as protons and electrons. Before they escaped the sun's atmosphere, however, some of the protons captured an electron, forming intact hydrogen atoms. The atoms left the sun in a fast, straight shot before they could be broken apart again." (For experts: The team believes the electrons were recaptured by some combination of radiative recombination and charge exchange.)

Second, what delayed the ions?

"Simple," says Mewaldt. "Ions are electrically charged and they feel the sun's magnetic field. Solar magnetism deflects ions and slows their progress to Earth. Hydrogen atoms, on the other hand, are electrically neutral. They can shoot straight out of the sun without magnetic interference."

Imagine two runners dashing for the finish line. One (the ion) is forced to run in a zig-zag pattern with zigs and zags as wide as the orbit of Mars. The other (the hydrogen atom) runs in a straight line. Who's going to win?

"The hydrogen atoms reached Earth almost two hours before the ions," says Mewaldt.

Mewaldt believes that all strong flares might emit hydrogen bursts, but they simply haven't been noticed before. He's looking forward to more X-flares now that the two STEREO spacecraft are widely separated on nearly opposite sides of the Sun. (In 2006 they were still together near Earth.) STEREO-A and –B may be able to triangulate future bursts and pinpoint the source of the hydrogen. This would allow the team to test their ideas about the surprising phenomenon.

"All we need now," he says, "is some solar activity."

For more information about this research, look for the article "STEREO Observations of Energetic Neutral Atoms during the 5 December 2006 Solar Flare" by R. A. Mewaldt et al., in a future issue of the Astrophysical Journal Letters.

For more information about STEREO, please visit: www.nasa.gov/stereo .

Provided by NASA's Goddard Space Flight Center

Explore further: Tiny satellites could be 'guide stars' for huge next-generation telescopes

Related Stories

Recommended for you

A fleeting moment in time

January 22, 2019

The faint, ephemeral glow emanating from the planetary nebula ESO 577-24 persists for only a short time—around 10,000 years, a blink of an eye in astronomical terms. ESO's Very Large Telescope captured this shell of glowing ...

Revealing the black hole at the heart of the galaxy

January 22, 2019

Including the powerful ALMA into an array of telescopes for the first time, astronomers have found that the emission from the supermassive black hole Sagittarius A* at the center of the galaxy comes from a smaller region ...

How hot are atoms in the shock wave of an exploding star?

January 21, 2019

A new method to measure the temperature of atoms during the explosive death of a star will help scientists understand the shock wave that occurs as a result of this supernova explosion. An international team of researchers, ...

New eclipsing cataclysmic variable discovered

January 21, 2019

Using the Mobile Astronomical System of Telescope-Robots (MASTER), an international team of astronomers has detected a new eclipsing cataclysmic variable. The newfound object, designated MASTER OT J061451.70–272535.5, is ...

The disintegrating exoplanet K2-22b

January 21, 2019

Exoplanet surveys have yielded many surprises over the years, and the discovery of "disintegrating" exoplanets was one of them. These are planets that produce asymmetric shapes in the dips of the light curves seen as they ...

Total lunar eclipse woos sky watchers

January 21, 2019

An unusual set of celestial circumstances came together over Sunday night and the wee hours of Monday for sky watchers in Europe, Africa and the Americas, where the moon was fully obscured before lighting up again with a ...

2 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

axemaster
5 / 5 (2) Dec 16, 2008
"(For experts: The team believes the electrons were recaptured by some combination of radiative recombination and charge exchange.)"

Thank you! Really! Thank you!

I'm glad they know we exist.
Thecis
not rated yet Dec 16, 2008
hahaha,
always nice to be recognised.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.