Venusian Half Shell
Credit & Copyright: K.Dennerl (MPE) et al.,
CXC,
NASA
Explanation:
Venus,
second planet from the Sun, appears above imaged for
the first time ever in x-rays (left) by the
orbiting
Chandra Observatory.
Chandra's smoothed, false-color, x-ray
view is compared to
an optical image (right) from a small earthbound telescope.
Both show Venus illuminated by the Sun from the right, with
only half the sunward hemisphere visible, but at least one
striking difference is apparent.
While the optical image in
reflected sunlight is filled and
bright at the center, Venus in x-rays is bright around the edge.
Venus' x-rays are produced
by
fluorescence rather than reflection.
About 120 kilometers or so above the surface,
incoming
solar x-rays
excite atoms in the
Venusian atmosphere
to unstable energy levels.
As
the atoms
rapidly decay back to their stable ground states they emit
a "fluorescence" x-ray, creating a glowing x-ray
half-shell above the sunlit hemisphere.
More
x-ray emitting
material can be seen looking at the edge
of the shell, so the edge appears brighter in the x-ray image.
Authors & editors:
Robert Nemiroff
(MTU) &
Jerry Bonnell
(USRA)
NASA Web Site Statements, Warnings,
and Disclaimers
NASA Official: Jay Norris.
Specific
rights apply.
A service of:
LHEA at
NASA /
GSFC
& Michigan Tech. U.
