Three days after the Mars Reconnaissance Orbiter's Aug. 12, 2005, launch,
the spacecraft was pointed toward Earth and the Mars Color Imager camera
was powered up to acquire a suite of images of Earth and the Moon. When it
gets to Mars, the Mars Color Imager's main objective will be to obtain
daily global color and ultraviolet images of the planet to observe martian
meteorology by documenting the occurrence of dust storms, clouds, and
ozone. This camera will also observe how the martian surface changes over
time, including changes in frost patterns and surface brightness caused by
dust storms and dust devils.
The purpose of acquiring an image of Earth and the Moon just three days
after launch was to help the Mars Color Imager science team obtain a
measure, in space, of the instrument's sensitivity, as well as to check
that no contamination occurred on the camera during launch. Prior to
launch, the team determined that, three days out from Earth, the planet
would only be about 4.77 pixels across, and the Moon would be less than
one pixel in size, as seen from the Mars Color Imager's wide-angle
perspective. If the team waited any longer than three days to test the
camera's performance in space, Earth would be too small to obtain
meaningful results.
The Earth and Moon images were acquired by turning Mars Reconnaissance
Orbiter toward Earth, then slewing the spacecraft so that the Earth and
Moon would pass before each of the five color and two ultraviolet filters
of the Mars Color Imager. The distance to the Moon was about 1,440,000
kilometers (about 895,000 miles); the range to Earth was about 1,170,000
kilometers (about 727,000 miles).
This view combines a sequence of frames showing the passage of Earth and
the Moon across the field of view of a single color band of the Mars
Color Imager. As the spacecraft slewed to view the two objects, they
passed through the camera's field of view. Earth has been saturated white
in this image so that both Earth and the Moon can be seen in the same
frame. The Sun was coming from the left, so Earth and the Moon are seen
in a quarter phase. Earth is on the left. The Moon appears briefly on the
right. The Moon fades in and out; the Moon is only one pixel in size, and
its fading is an artifact of the size and configuration of the
light-sensitive pixels of the camera's charge-coupled device (CCD)
detector.