orb
New member
- Joined
- Oct 30, 2009
- Messages
- 14,020
- Reaction score
- 4
- Points
- 0
It's been a mystery for more than half a century: why, in the short distance from the Sun's surface to its corona, or outer atmosphere, does the temperature leap from a few thousand to a few million degrees? Now scientists believe they have discovered a major source of hot gas that replenishes the corona: narrow jets of plasma, known as spicules, shooting up from just above the Sun’s surface. The finding addresses a fundamental question in astrophysics: how energy moves from the Sun’s interior to create its hot outer atmosphere.
Observations from NASA's Solar Dynamics Observatory (SDO) and the Japanese satellite Hinode show that some gas in the giant, fountain-like jets in the sun's atmosphere known as spicules can reach temperatures of millions of degrees. The finding offers a possible new framework for how the sun's high atmosphere gets so much hotter than the surface of the sun.
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.
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.
Now, De Pontieu's team -- which included researchers at Lockheed Martin, the High Altitude Observatory of the National Center for Atmospheric Research (NCAR) in Colorado and the University of Oslo, Norway -- was able to combine images from SDO and Hinode to produce a more complete picture of the gas inside these gigantic fountains.
Other solar physicists agree that the work of De Pontieu's group is a major development, but say that it is not the end of the corona mystery. James Klimchuk of NASA's Goddard Space Flight Center in Greenbelt, Maryland, says that he has performed preliminary calculations showing that the plasma jets actually account for only a small proportion of the coronal heating. "The new observations are very exciting, but the jury is still out on the importance of jets in the big scheme of things," he says.
Mike Wheatland at the Sydney Institute for Astronomy in Australia also thinks that the mechanism is less than clear-cut. "The estimate of the energy supplied by the observed events is of the order required, as the authors state, but the events are localized and occur low in the corona, and coronal heating is required essentially everywhere," he says.
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. IRIS will 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 mechanisms.
Links:
Observations from NASA's Solar Dynamics Observatory (SDO) and the Japanese satellite Hinode show that some gas in the giant, fountain-like jets in the sun's atmosphere known as spicules can reach temperatures of millions of degrees. The finding offers a possible new framework for how the sun's high atmosphere gets so much hotter than the surface of the sun.
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.
"It's always been quite a puzzle to figure out why the Sun's atmosphere is hotter than its surface," says Scott McIntosh, a solar physicist at the High Altitude Observatory of the National Center for Atmospheric Research (NCAR) in Boulder, Colo., who was involved in the study.
"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.
"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.
[table="head;width=500]{colsp=2}
|
{colsp=2}
{colsp=2}
Click on images to enlarge
|
Spicules on the sun, as observed by the Solar Dynamics Observatory. These bursts of gas jet off the surface of the sun at 150,000 miles per hour and contain gas that reaches temperatures over a million degrees. Credit: NASA Goddard/SDO/AIA
|Solar spicules as imaged by NASA's Solar Dynamics Observatory. Credit: NASA
{colsp=2}
{colsp=2}
Multiwavelength extreme ultraviolet image of the Sun taken by the Solar Dynamics Observatory's Atmospheric Imaging Assembly. Colours represent different gas temperatures: ~800,000 Kelvin (blue), ~1.3 million K (green), and ~2 million K (red). New observations reveal jets of hot plasma propelled upwards from the region immediately above the Sun's surface. Image: Bart De Pontieu)
[/table]Now, De Pontieu's team -- which included researchers at Lockheed Martin, the High Altitude Observatory of the National Center for Atmospheric Research (NCAR) in Colorado and the University of Oslo, Norway -- was able to combine images from SDO and Hinode to produce a more complete picture of the gas inside these gigantic fountains.
Other solar physicists agree that the work of De Pontieu's group is a major development, but say that it is not the end of the corona mystery. James Klimchuk of NASA's Goddard Space Flight Center in Greenbelt, Maryland, says that he has performed preliminary calculations showing that the plasma jets actually account for only a small proportion of the coronal heating. "The new observations are very exciting, but the jury is still out on the importance of jets in the big scheme of things," he says.
Mike Wheatland at the Sydney Institute for Astronomy in Australia also thinks that the mechanism is less than clear-cut. "The estimate of the energy supplied by the observed events is of the order required, as the authors state, but the events are localized and occur low in the corona, and coronal heating is required essentially everywhere," he says.
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. IRIS will 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 mechanisms.
Links:
- NASA:
- Science:
- NCAR & UCAR News Center: Plasma jets are prime suspect in solar mystery
- National Science Foundation: Longstanding Mystery of Sun's Hot Outer Atmosphere Solved
- SPACE.com: Sun's Super-Hot Shell Cooked by Plasma Jets
- SpaceRef: Plasma Jets Could Solve Mystery of Solar Heating
- Space Daily: Hotspots In Fountains On The Sun's Surface Help Explain Coronal Heating Mystery
- PhysicsWorld: Physicists find new clue in coronal heating mystery
- ScienceNews: Superhot solar mystery may be solved
- Discovery News: New Clue May Solve Solar Mystery
- Nature: Plasma jets key to enduring solar mystery
- Universe Today: Previously Unseen Super-Hot Plasma Jets Heat the Sun’s Corona
- Ars Technica: Plasma jets make Sun's corona so much hotter than the surface
- Scientific American: Plasma Jets Pump Heat into the Sun's Sizzling Corona
- e! Science News: Hotspots in fountains on the sun's surface help explain coronal heating mystery
- redOrbit: Fountain Hotspots Help Explain Coronal Heating Mystery
