* Astronomy

A team of scientists has scanned the northern polar region of Earth with the Chandra X-ray Observatory. The results show that the aurora borealis, or "northern lights," also produce X-rays, and create changing bright arcs 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 (0.1 - 10 kilo electron volts) generated for the first time during auroral activity.


Expand (502kb, 792 x 612)

The researchers, led by Dr. Ron Elsner of NASA's Marshall Space Flight Centre in Huntsville, Alabama, observed 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, from about 120,000 km away, and the Earth's motion carried the auroral regions through Chandra's field of view.
From the ground, the auroras are known to change dramatically over time, and this is also the case in X-ray light. The X-rays in this sample of the Chandra observations, which have been superimposed on an approximate representation of the Earth, are seen here.
Auroras are produced by solar storms that eject clouds of energetic charged particles. These particles are deflected when they encounter the Earth's magnetic field, but in the process large electric voltages are created. Electrons trapped in the Earth's magnetic field are accelerated by these voltages and spiral along the magnetic field into the Polar Regions. There they collide with atoms high in the atmosphere and emit X-rays. Chandra has also observed dramatic auroral activity on Jupiter.

Dr. Anil Bhardwaj is the lead author on a paper describing these results in the Journal of Atmospheric and Solar-Terrestrial Physics. Dr. Bhardwaj was a co-investigator on this project and worked with Dr. Elsner at NASA's Marshall Space Flight Centre while this research was conducted.