First scientists trace the fastest solar particles to their roots on the Sun.

First, scientists track the fastest solar particles to their roots in the sun

A solar flare from AR 11944 was emitted on January 7, 2014 seen in several different wavelengths of light from NASA’s Solar Dynamics Observatory. From right to left, the artificial color images show plasma at about 1 million degrees Celsius, 4.5 million degrees Celsius (2.5 million degrees Celsius), and 12.7 million degrees Celsius (7.1 million degrees Celsius). Credits: NASA / SDO

Zipping through space close to the speed of light, Solar Energy Eros, or SEP, is one of the main challenges for the future of human space travel. Clouds from these tiny solar projectiles can reach Earth – 93 million miles of travel – in less than an hour. They can fry sensitive spacecraft electronics and pose serious risks to human astronauts. But their appearance is extraordinarily difficult to predict, in part because we still don’t know exactly where they come from from the Sun.

A new study tracking three SEP explosions to the Sun gave the first answer.

“We were able to indicate for the first time the specific sources of these energy particles,” said Stephanie Yardley, a cosmic physicist at University College London and co-author of the journal. “Understanding the source regions and physical processes that produce SEPs could lead to an improved prediction of these events.” Study authors David Brooks, a space physicist at George Mason University in Washington, DC, and Yardley published their findings in Scientific Advances on March 3, 2021.

SEPs can shoot from the Sun in any direction; capturing one in the vastness of space is not small. NASA’s Heliophysical System Observatory – a growing fleet of spacecraft studying the Sun, strategically located across the solar system – was designed in part to increase the chances of those lucky encounters.

Scientists have divided SEP events into two main types: impulsive and gradual. Impulsive SEP events usually occur after solar flares, the bright flashes on the Sun produced by abrupt magnetic eruptions.

“It’s this very sharp sting, and then an exponential decay over time,” said Lynn Wilson, a project scientist for the Wind spacecraft at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

Gradually SEP lasts longer, sometimes for days. They come in large swarms, making the explosions a greater risk for astronauts and satellites. Gradually SEPs are propelled from behind by corona massive ejections, or CME-sized feathers of solar material that swell through space like a wave. The SEPs act like surfers, trapped by that wave and driven at incredible speeds.

The biggest mystery about gradual SEPs is not what speeds them up, but where they first come from. For reasons not yet fully understood, SEP contains a different mixture of particles than the other solar material flowing from the Sun in the solar wind – for example less carbon, sulfur and phosphorus ions. Some scientists suspect that they are cut from a completely different cloth, forming in a different feature or layer of the Sun than the rest of the solar wind.

First, scientists track the fastest solar particles to their roots in the sun

A close-up view of one of the AR 11944 flares emitted on 7 January 2014. This flare may be how the SEPs detected by Wind were released from the Sun. Credits: NASA / SDO

To find out where SEP comes from, Brooks and Yardley tracked gradual SEP events from January 2014 to their origin at the Sun.

They started with NASA’s Wind spacecraft, which orbits at the L1 Lagrange point about 1 million miles closer to the Sun than us. One of Wind’s eight instruments is the Energy Particles: Acceleration, Composition, and Transport, or an EPACT instrument that specializes in detecting SEPs. EPACT captured three strong SEP explosions on 4, 6 and 8 January.

Wind’s data showed that these SEP events actually had a specific “fingerprint” – a different mix of particles than is usually found in the solar wind.

“There is often less sulfur in SEP compared to the solar wind, sometimes much less,” said Brooks, the newspaper’s lead author. “This is a unique fingerprint of SEPs that allows us to look for places in the Solar atmosphere where sulfur is also lacking.”

They turned to Sun-staring JAXA / NASA’s Hinode spacecraft, an observatory in which Brooks plays a critical functional role for NASA of Japan. Hinode looked at Active Region 11944, a bright area of ​​strong magnetic field with a large dark sunspot visible from Earth. AR 11944 produced several large flares and CME in early January, which released and accelerated the SEP Wind observed.

Hinode’s Extreme Ultraviolet Imaging Spectrometer, or EIS instrument, scanned the active region, breaking the light into spectral lines used to identify specific elements. They searched for locations in the active region with a compatible fingerprint, where the specific mix of elements matched what they saw in the Wind data.

“This kind of research is exactly what Hinode aimed to continue,” said Sabrina Savage, the U.S. project scientist at Hinode. “Complex system science cannot be done in a bubble with just one mission.”

Hinode’s data revealed the source of the SEP events – but that was not expected of Brooks or Yardley.

Usually the solar wind can escape more easily by finding open magnetic field lines – field lines anchored to the Sun at one end but flowing into space on the other.

First, scientists trace the fastest solar particles to their roots in the sun

Closed magnetic field lines connect back to the Sun, surrounded by open field lines that extend into space, as illustrated in this illustration. Credits: NASA’s Goddard Space Flight Center / Lisa Poje / Genna Duberstein

“I really thought we’d find it at the edges of the active region where the magnetic field is already open and material can escape directly,” Brooks said. “But the fingerprint matched only in regions where the magnetic field is still closed.”

The SEP was somehow freed from strong magnetic loops connected to the Sun at both ends. These loops trap material near the top of the chromosphere, one layer below, where solar flames erupt and corona massive ejections.

“People have already been thinking of ways it could get out of a closed field – especially in the context of the solar wind,” Brooks said. “But I think the fact that the material was found in the core of the region where the magnetic fields are very strong makes it difficult for those processes to function.”

The surprising result raises new questions about how SEPs escape from the Sun, questions ripe for future work. However, indicating the source of one event is a big step forward.

“Usually you have to conclude such things – you’d say,‘ look, we’ve seen SEP and solar flare, and the SEP probably came from the solar flare, ”said Wilson, who was not involved in the study. “But this is direct proof linking these two phenomena together.”

Brooks and Yardley also show one way to use NASA’s growing Heliophysical Systems Observatory, combining multi-spacecraft observations to make science previously impossible.

“It’s a way to think about all the flying spaceships you can use to do one study,” Wilson said. “It’s like having a lot of weather stations – you get a much better picture of what the weather is doing on a larger scale, and you can actively try to predict it.”

“These authors have done a remarkable job combining the right data sets and applying them to the right questions,” Savage said. “The search for the origins of potentially harmful energy particles has been critically diminished thanks to this effort.”

A source of dangerous high-energy particles located in the Sun.

Additional information:
David H. Brooks et al. The source of the most important solar particles of overactive region 11944, Scientific Advances (2021). DOI: 10.1126 / sciadv.abf0068

Provided by NASA’s Space Flight Center

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