Sun-watching satellite observes solar eruption in unprecedented detail

Washington, May 24 : A sun-watching satellite has observed a solar eruption in unprecedented detail, revealing new features that are predicted by computer models but difficult to see in practice.

Such eruptions, called coronal mass ejections (CME), occur when a giant bubble of hot plasma and magnetic field lines blasts outward from the sun at speeds of up to 1,500 miles per second.hey happen periodically and pose a potential threat to astronauts or satellites if aimed at Earth.

Astronomers study these explosions in hope of being able to predict them and provide "space weather" forecasts.

The latest CME was observed using the Smithsonian-developed X-ray Telescope (XRT) aboard the Hinode sun-watching satellite.

It occurred on the edge or limb of the Sun as viewed from Earth. As a result, the X-ray brightening (solar flare) usually associated with a CME was hidden from view, allowing the sun-watching spacecraft to take longer exposures and uncover fainter structures than usual.

Using the XRT, astronomers saw a spiral magnetic structure unwind as it left the Sun during the CME. Such unwinding can release energy as the magnetic field goes from a more twisted to a less twisted configuration, thereby helping to power the eruption.

"Observations like this are very rare," said Smithsonian astronomer Ed DeLuca.

Hours later, XRT revealed an inflow of material toward a feature that appears as a bright line-actually an object known as a current sheet seen edge-on.

A current sheet is a thin, electrified sheet of gas where oppositely directed magnetic field lines annihilate one another in a process known as magnetic reconnection.

The extended observations from XRT show that magnetic fields flow in toward the current sheet for many hours after the eruption, progressing first toward the sheet and then down to the sun's surface.

Computer models of CMEs predict such movements of magnetic field lines, but observing them has proven difficult.

But, the unique positioning of this CME on the sun's limb allowed astronomers to measure those motions.

They also determined that the temperature of the current sheet is between 5 and 18 million degrees Fahrenheit, which matches previous measurements higher up in the corona by the Ultraviolet Coronagraph Spectrometer on the SOHO spacecraft.

ANI