In a paper published today in the journal Science, researchers -- from the Solar and Astrophysics Laboratory (LMSAL) of the Lockheed Martin Advanced Technology Center (ATC), along with colleagues at the High Altitude Observatory (HAO) of the National Center for Atmospheric Research (NCAR) in Colorado and the University of Oslo, Norway -- have discovered a major source of hot gas that replenishes the Sun's outer atmosphere, or corona. 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 -- both designed and built at the ATC.
The visible surface of the Sun, called the photosphere, is relatively cool, at 6,000 degrees C, but is enveloped by the much hotter gas of the corona. One of the most enduring mysteries in solar physics is why the Sun's corona is millions of degrees hotter than its surface. During the past few decades, a wide variety of theoretical models to explain this enigma have been proposed, but the lack of detailed observations of the fundamental heating process has significantly hampered progress.
Spicules are phenomena that have held particular promise as discrete coronal heating events for decades. "Heating of spicules to millions of degrees has never been observed, so their role in coronal heating had been dismissed as unlikely," said Dr. Bart De Pontieu, a solar physicist at LMSAL who led the investigation. Waving from side to side like a field of wheat in a gentle breeze, spicules are fountains in which relatively cool gas or plasma is propelled upwards from the surface into the outer atmosphere at supersonic speeds. Moving at about 300,000 km per hour, a spicule would travel the distance between San Francisco and London in just a few minutes.
"Our observations reveal, for the first time, that a substantial portion of the cool spicule gas is actually heated to millions of degrees, supplying hot plasma to the corona," said Dr. Scott McIntosh, a solar physicist at HAO who coordinated the joint observations between the two solar space telescopes that the team used. The high spatial and temporal resolution of AIA and SOT were crucial in revealing this previously hidden coronal mass supply. The team found that the heated spicules likely occur often enough to continuously replenish the corona.
These findings provide a significant challenge to existing theories of coronal heating. "Our challenge now is to understand what drives and heats the material in the spicules," said Dr. De Pontieu. The surprising results highlight the importance of the poorly understood interface region between the photosphere and the corona, for a better understanding of the whole outer solar atmosphere. NASA's next Small Explorer mission, the Interface Region Imaging Spectrograph scheduled for launch in 2012, will provide high fidelity data on the complex processes and enormous contrasts of density, temperature and magnetic field within this region.
Note to Editors
The following links point to movies that illustrate points made in the Science paper:
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The Solar and Astrophysics Laboratory at the ATC conducts basic research into understanding and predicting space weather and the behavior of our Sun including its impacts on Earth and climate. It has a 47-year-long heritage of spaceborne solar instruments including the Soft X-ray Telescope on the Japanese Yohkoh satellite, the Michelson Doppler Imager on the ESA/NASA Solar and Heliospheric Observatory, the solar telescope on NASA's Transition Region and Coronal Explorer, the Focal Plane Package on the Japanese Hinode satellite, the Solar X-ray Imagers on GOES-N, -O and -P, the Extreme Ultraviolet Imager instruments on NASA's twin STEREO spacecraft, and the Heliospheric and Magnetic Imager and the Atmospheric Imaging Assembly on NASA's Solar Dynamics Observatory.
The ATC is the research and development organization of Lockheed Martin Space Systems Company (LMSSC). LMSSC, a major operating unit of Lockheed Martin Corporation, designs and develops, tests, manufactures and operates a full spectrum of advanced-technology systems for national security and military, civil government and commercial customers. Chief products include human space flight systems; a full range of remote sensing, navigation, meteorological and communications satellites and instruments; space observatories and interplanetary spacecraft; laser radar; ballistic missiles; missile defense systems; and nanotechnology research and development.
Headquartered in Bethesda, Md., Lockheed Martin is a global security company that employs about 133,000 people worldwide and is principally engaged in the research, design, development, manufacture, integration and sustainment of advanced technology systems, products and services. The Corporation's 2009 sales from continuing operations were $44.0 billion.