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Plasma 'bombs' and tornadoes detected on the Sun

Violent Sun The first detailed view of a poorly understood region of the Sun reveals plasma 'bombs', powerful tornadoes, and supersonic jets that may be the start of the solar wind.

These observations, reported in five papers in the journal Science, will help scientists determine how massive amounts of energy generated by the Sun are transported from its surface to its outer atmosphere.

The features were detected by NASA's new IRIS space telescope, which studies the mysterious interface region that sits between the Sun's surface (photosphere) and the outer atmosphere (corona).

"IRIS's findings tell us the interface region of the Sun is far more complicated than we imagined," says Dr Hui Tian of the Harvard-Smithsonian Centre for Astrophysics, who is an author on four of the papers.

The interface region is composed of the chromosphere and a transition layer between the chromospheres and corona.

"It's not the thin static layer predicted in solar atmospheric models. There's a sharp temperature change from the 6000-degree photosphere to the corona where temperatures reach over a million degrees, and the interface region is where this change occurs," says Tian.

The region emits mostly ultraviolet light, which can be best studied in high resolution detail from space.

Using imaging and spectrometry, IRIS traces temperature differences within the chromosphere, as well as the speed, density and turbulence of dynamic plasma particles.

Tian and colleagues used IRIS to observe activity inside coronal holes where they discovered high-speed jets that may contribute plasma to the solar wind, the stream of particles constantly flowing from the Sun, which generates space weather on Earth.

"This unprecedented high resolution lets us examine various types of previously unseen features such as very small scale intermittent high speed jet-like structures in the interface region," says Tian.

"This region is believed to be where the solar wind originates, and these jets are the most prominent dynamic features in this region. The most natural question is: are they the initial stage of the solar wind?

"If they are, then our solar wind models will need to be updated."

Plasma bombs and tornadoes

The authors also discovered pockets of hot 100,000-degree plasma embedded in the surrounding relatively cool 6000-degree photosphere.

"The temperature contrast creates 'bombs of hot plasma', which had never been seen before, and which were totally unexpected," says Tian.

Tian and colleagues believe the plasma bombs are generated by magnetic reconnection, a process that occurs when magnetic field lines connect and disconnect explosively, transferring energy.

Another surprise for researchers was the discovery of twisting tornado- like structures in the chromosphere.

"A lot of fine-scale structures in the chromosphere are rotating, which was not what we expected," says Tian.

"These rotation motions can transfer mass and energy from the lower to the higher layers of atmosphere, none had never been seen before, and that's very exciting."

The authors also studied the creation of long magnetic loops in the Sun's active regions which accelerate particles to very high energies, and they confirmed the existence of short magnetic loops, which had been an issue of debate for many years.

IRIS, which was launched last year, will continue observing the Sun for the next decade

"We are only just starting to analyse the IRIS data," says Tian.

"In the next few years more exciting things will be discovered."