29 December 2005

Chandra Turns Earthbound!

On February 15, 2004, Chandra observed X-rays produced by an aurora in the north-polar region of Earth. The X-rays, superimposed on a model of Earth, are seen as the violet-yellow-red arc stretching from northern Canada on the upper left to the Hudson Bay on the lower right. To obtain this data, Chandra was aimed at a fixed point in the sky, and the Earth's motion carried the auroral regions through the field of view. The shadowed area defines the day-night boundary at sea level. The X-ray activity is taking place at approximately 100 kilometers above the Earth. Scale: Distance from the North pole to the black circle is 3,340 km (2,075 miles)

Now this came as a welcome surprise to me. The Chandra X-Ray Observatory has been returning marvelous science for some time now, but I was unaware that direct terrestrial study was within its capabilities! This new press release contains some really neat tidbits:

Image Credits: NASA/MSFC/CXC/A.Bhardwaj & R.Elsner, et al.;
Earth model: NASA/GSFC/L.Perkins & G.Shirah

In an unusual observation, a team of scientists has scanned the northern polar region of Earth with NASA's Chandra X-ray Observatory. The results show that the aurora borealis, or "northern lights," also dance in X-ray light, creating changing bright arcs of X-ray energy above the Earth's surface.

While other satellite observations had previously detected high-energy X-rays from the Earth auroras, the latest Chandra observations reveal low-energy X-rays generated during auroral activity for the first time.

The researchers, led by Dr. Ron Elsner of NASA's Marshall Space Flight Center in Huntsville, Ala., used Chandra to observe the Earth 10 times over a four-month period in 2004. The images were created from approximately 20-minute scans during which Chandra was aimed at a fixed point in the sky and the Earth's motion carried the auroral regions through Chandra's field of view.

From the ground, the aurora are well known to change dramatically over time and this is the case in X-ray light as well. The X-rays in this sample of the Chandra observations, which have been superimposed on a simulated image of the Earth, are seen here at four different epochs.


Speaking of aurorae, Dr. Tony Phillips has just added a most impressive "mega-gallery" of aurora photographs, including every single image ever posted on Spaceweather.com. If you haven't surfed the aurora galleries there in the past, be sure to check it out -- I could kill untold hours there. For more, also visit this page devoted to aurorae courtesy of the Exploratorium.

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