Mystery of Solar Corona being far hotter than the sun’s surface resolved

A new paper has just appeared in Science dated 7th Jan (wow, its still only 6th, have I just fallen into a time rift?).

Anyway, they appear to have unraveled a mystery. For quite some time it has been known that the solar corona is far hotter than the sun’s surface by millions of degrees, so how the heck is this possible, what mechanism might explain this? Well, we now appear to have an answer. Apparently jets of super hot plasma shoot up from the surface of the sun and replenishes the corona.

For decades scientists believed spicules could send heat into the corona. However, following observational research in the 1980s, it was found that spicule plasma did not reach coronal temperatures, and so the theory largely fell out of vogue.

Heating of spicules to millions of degrees has never been directly observed, so their role in coronal heating had been dismissed as unlikely,” says Bart De Pontieu, the lead researcher and a solar physicist at LMSAL.

In 2007, De Pontieu, McIntosh, and their colleagues identified a new class of spicules that moved much faster and were shorter-lived than the traditional spicules.

These “Type II” spicules shoot upward at high speeds, often in excess of 100 kilometers per second, before disappearing.

The rapid disappearance of these jets suggested that the plasma they carried might get very hot, but direct observational evidence of this process was missing.

The researchers used new observations from the Atmospheric Imaging Assembly on NASA’s recently launched Solar Dynamics Observatory and NASA’s Focal Plane Package for the Solar Optical Telescope (SOT) on the Japanese Hinode satellite to test their hypothesis.

“One of our biggest challenges is to understand what drives and heats the material in the spicules,” says De Pontieu.

A key step, according to De Pontieu, will be to better understand the interface region between the Sun’s visible surface, or photosphere, and its corona.

Another NASA mission, the Interface Region Imaging Spectrograph (IRIS), is scheduled for launch in 2012 to provide high-fidelity data on the complex processes and enormous contrasts of density, temperature and magnetic field between the photosphere and corona. Researchers hope this will reveal more about the spicule heating and launch mechanism.

The abstract for the paper in science can be found here, and the paper is titled, “The Origins of Hot Plasma in the Solar Corona”.

You can also read more about this discovery on Science Daily here.

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