This work has identified jetsemerging from beneath the surface of the sun passing upward and then fallingback but leaving super heated remnants behind in the corona. It is mechanical but a clear path to causinga hotter corona than can be modeled otherwise.
And when you can see ithappening, it is a good bet to go with.
The visible surface layer is comparativelycool, so some mechanism was needed to deliver heat to the corona and it was ariddle.
Jets implicated in solar riddle
7 January 2011 Last updated at 05:58 ET
This extreme ultraviolet image of the Sun shows different gastemperatures: 800,000 Celcius (blue), 1.3 million C (green), and 2 million C(red)
Scientists say they are closer to understanding why the Sun's outeratmosphere is hotter than its surface.
The corona, as it is known, is millions of degrees hotter than thestar's visible surface layer, or photosphere.
Two satellites have now identified jets of super-heated gas, calledspicules, shooting up from just above the Sun's surface into the outeratmosphere.
Researchers tell the journalScience that this process could be what maintains the temperaturedifference.
"It's always been quite a puzzle to figure out why the Sun'satmosphere is hotter than its surface," said Scott McIntosh, from the
US for AtmosphericResearch (NCAR), a co-author on the Science study. National Center
"By identifying that these jets insert heated plasma into theSun's outer atmosphere, we gain a greater knowledge of the corona and possiblyimprove our understanding of the Sun's subtle influence on Earth's upperatmosphere."
Spicules have long been thought to play a role in coronal heating butprevious observations have never had the resolution to study their behaviour insufficient detail.
The step change has come from new satellites in orbit. This researchcombined the observational power of
's Hinode spacecraft and theAmerican Solar Dynamics Observatory, which was launched just last year. Japan
These platforms watched as the spicules shot up through the lower solaratmosphere in remarkable volume and at tremendous speed.
The amount of material being sent up into the corona is about 100 timesas much as streams away from the Sun in the solar wind towards the edges of theSolar System, say the scientists. And the jets are moving at about 300,000km/h,they add.
The research found that a large fraction of the gas is heated to ahundred thousand degrees, while a small fraction is heated to millions ofdegrees.
Time-lapsed images show that while much of the material which spewsupwards comes straight back down, a small fraction of the gas that is heated tomillions of degrees does not immediately return to the surface.
Given the large number of spicules on the Sun, and the amount ofmaterial in the spicules, the scientists believe that if even some of thatsuper-hot plasma stays aloft it would make a contribution to coronal heating.
"Our challenge now is to understand what drives and heats thematerial in the spicules," said Dr Bart De Pontieu from the Solar andAstrophysics Laboratory of the Lockheed Martin, which made SDO for the US spaceagency (Nasa).