Original Caption Released with Image:
On May 19th, 2005, NASA's Mars Exploration Rover Spirit captured this stunning
view as the Sun sank below the rim of Gusev crater on Mars. This Panoramic
Camera (Pancam) mosaic was taken around 6:07 in the evening of the rover's
489th martian day, or sol. Spirit was commanded to stay awake briefly after
sending that sol's data to the Mars Odyssey orbiter just before sunset. This
small panorama of the western sky was obtained using Pancam's 750-nanometer,
530-nanometer and 430-nanometer color filters. This filter combination allows
false color images to be generated that are similar to what a human would see,
but with the colors slightly exaggerated. In this image, the bluish glow in
the sky above the Sun would be visible to us if we were there, but an artifact
of the Pancam's infrared imaging capabilities is that with this filter
combination the redness of the sky farther from the sunset is exaggerated
compared to the daytime colors of the martian sky. Because Mars is farther
from the Sun than the Earth is, the Sun appears only about two-thirds the size
that it appears in a sunset seen from the Earth. The terrain in the foreground
is the rock outcrop "Jibsheet", a feature that Spirit has been investigating
for several weeks (rover tracks are dimly visible leading up to "Jibsheet").
The floor of Gusev crater is visible in the distance, and the Sun is setting
behind the wall of Gusev some 80 km (50 miles) in the distance.
This mosaic is yet another example from MER of a beautiful, sublime martian
scene that also captures some important scientific information. Specifically,
sunset and twilight images are occasionally acquired by the science team to
determine how high into the atmosphere the martian dust extends, and to look
for dust or ice clouds. Other images have shown that the twilight glow remains
visible, but increasingly fainter, for up to two hours before sunrise or after
sunset. The long martian twilight (compared to Earth's) is caused by sunlight
scattered around to the night side of the planet by abundant high altitude
dust. Similar long twilights or extra-colorful sunrises and sunsets sometimes
occur on Earth when tiny dust grains that are erupted from powerful volcanoes
scatter light high in the atmosphere.
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