By Ron Cowen
Fountainlike jets of hot gas that shoot into the sun’s outer atmosphere may explain why this outlying region is millions of degrees hotter than the sun’s roiling surface — a puzzle that researchers have struggled to explain since they first took the solar corona’s temperature seven decades ago.
The newly discovered jets, too narrow and short-lived to have been seen with older instruments, were imaged in visible light by a high-resolution telescope aboard Japan’s Hinode craft, launched in 2006. Ultraviolet observations with NASA’s recently launched Solar Dynamics Observatory revealed that just seconds after the appearance of the jets in the sun’s chromosphere — the region just above the visible surface — the outer atmosphere, or corona, briefly brightened at temperatures ranging from 100,000 to as high as 2 million kelvins.
Although only a small fraction of the jets may carry hot gas, calculations show that the jets can transport enough high-temperature material to keep the corona heated to several million kelvins, says Bart De Pontieu of the Lockheed Martin Solar and Astrophysics Laboratory in Palo Alto, Calif. He and his colleagues describe their findings in the Jan. 7 Science.
“This is an important and startling breakthrough in understanding how the solar corona may be heated, and I am certainly convinced by it,” comments solar researcher Eric Priest of the University of St. Andrews in Scotland.