Giving off a Faint X-Ray Glow. (Martian Radiation)

Article excerpt

X rays from the Red Planet! That may sound like the title of a low-budget sci-fi flick, but it could actually be the label for a documentary. Using an Earth-orbiting telescope to record what Mars would look like if our eyes were sensitive to high-energy radiation, researchers have for the first time detected X-ray emissions from the planet.

Mars requires a partner to generate these rays. X rays from the sun induce the emissions when they interact with atoms in Mars' upper atmosphere. The atoms absorb the radiation and reemit it at a lower X-ray energy, a process known as fluorescent scattering.

The X rays come primarily from a region 90 to 160 kilometers above the Martian surface, reports Konrad Dennerl of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany. He reports the findings in a mid-November issue of Astronomy & Astrophysics.

"With X rays, we have direct observational access to the upper Martian atmosphere, which is difficult to study by other means," he notes. Because each type of atmospheric atom fluoresces at a different X-ray wavelength, Dennerl says, "the Martian X rays contain information about the chemical composition of its upper atmosphere"

Merely detecting the planet's faint X-ray glow is an accomplishment, he notes. During the 9 hours that the Chandra X-ray Observatory stared at Mars in Dennerl's study, the satellite recorded only about 300 X-ray photons. These Martian X rays show features similar to those that Chandra recorded from Venus' atmosphere (SN: 12/8/01, p. …