Skygazing from Mars: Earth and Jupiter Align
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The Mars Orbiter Camera aboard the Mars Global Surveyor spacecraft usually looks down, capturing some of the most detailed images ever seen of the Red Planet's surface. On May 8, at 13:00 UT, camera operators at Malin Space Science Systems in San Diego turned the instrument the other way and looked homeward. At that time, martian sky watchers would have seen Earth and Jupiter in close alignment in the evening sky. Scientists took advantage of the opportunity to make portraits of both planets, the first planetary conjunction viewed from another world.
Enlarged view of the crescent Earth and moon as seen from Mars. |
Other spacecraft have given us images of the Earth and moon together. The Galileo and Near Earth Asteroid Rendezvous spacecraft each captured Earth and moon during fly-by maneuvers in 1990 and 1998, respectively. Voyager 1 looked back as it left for Jupiter, imaging both disks from 11 million kilometers in 1979.
In 1973, the Mercury-bound Mariner 10 spacecraft recorded hundreds of images of Earth and moon in the first few days after launch. Mariner 10 was the first spacecraft capable of returning high-resolution digital color image data. In fact, scientists at Malin Space Science Systems used Mariner 10 images of Earth as a guide for adding artificial color to the black-and-white data returned by their camera.
 Mariner 10 mosaics of Earth and moon were combined to show the relative sizes of our home planet and its satellite. |
The result is the first image of Earth ever taken from another world that actually shows our home as a planetary disk. Because Earth and the moon are closer to the sun than Mars, they exhibit phases, just as the moon, Venus, and Mercury do when viewed from Earth.
Because our planet is far brighter than the moon, the image required special processing to allow both Earth and moon to be visible together. At the time the image was taken, Earth was of magnitude -2.5 in the martian sky -- that's almost as bright as Mars will be in our own sky in August -- but the moon shone at just +0.9 magnitude. The bright area at the top of the Earth image is cloud cover over central and eastern North America. Below that, a darker area includes Central America and the Gulf of Mexico. The bright feature near the center-right of the crescent Earth consists of clouds over northern South America. Earth and Mars were 139 million kilometers apart when the image was taken.
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Jupiter and (from left to right) its moons Callisto, Ganymede and Europa, as seen by the Mars Orbiter Camera May 8. NASA/JPL/Malin Space Science Systems. |
At nearly a billion kilometers away, the giant planet Jupiter was over five times more distant. Yet the Mars Orbiter Camera could see detail in Jupiter's cloud bands and capture three of its four largest satellites. Callisto and Ganymede (left), are roughly the size of the planet Mercury. Europa (right) and Io (not seen), are approximately the size of Earth's moon. Jupiter had an apparent brightness of -1.8 magnitude at the time the image was taken. Colors added to Jupiter were based on Cassini spacecraft images.
