Cassini images Earth
beneath Saturn’s rings
NASA’s Cassini spacecraft captured color images of Earth and the
moon from its perch in the Saturn system nearly 900 million miles (1.5 billion
kilometers) away on July 19. Meanwhile, MESSENGER, the first probe to
orbit Mercury, took a black-and-white image from a distance of 61 million
miles (98 million kilometers) as part of a campaign to search for natural
satellites of the planet.
In the Cassini images Earth and the moon appear as mere dots -- Earth
a pale blue and the moon a stark white, visible between Saturn’s rings. It
was the first time Cassini’s highest-resolution camera captured Earth and
its moon as two distinct objects.
“We can’t see individual continents or people in this portrait of Earth,
but this pale blue dot is a succinct summary of who we were on July
19,” said Linda Spilker, Cassini project scientist, at NASA’s Jet Propulsion
Laboratory in Pasadena, Calif. “Cassini’s picture reminds us how tiny our
home planet is in the vastness of space, and also testifies to the ingenuity
of the citizens of this tiny planet to send a robotic spacecraft so far away
from home to study Saturn and take a look-back photo of Earth.”
Pictures of Earth from the outer solar system are rare because from
that distance, Earth appears very close to our sun. A camera’s sensitive
detectors can be damaged by looking directly at the sun, just as a human
being can damage his or her retina by doing the same. Cassini was able
to take this image because the sun had temporarily moved behind Saturn
from the spacecraft’s point of view and most of the light was blocked.
“It thrills me to no end that people all over the world took a break from
their normal activities to go outside and celebrate the interplanetary
salute between robot and maker that these images represent,” said
Carolyn Porco, Cassini imaging team lead at the Space Science Institute
in Boulder, Colo. “The whole event underscores for me our ‘coming of
age’ as planetary explorers.”
In the MESSENGER image, Earth and the moon are less than a pixel, but
appear very large because they are overexposed. Long exposures are
required to capture as much light as possible from potentially dim objects.
Consequently, bright objects in the field of view become saturated and
appear artificially large.
“That images of our planet have been acquired on a single day from
two distant solar system outposts reminds us of this nation’s stunning
technical accomplishments in planetary exploration,” said MESSENGER
Principal Investigator Sean Solomon of Columbia University’s LamontDoherty Earth Observatory in Palisades, N.Y. “And because Mercury and
Saturn are such different outcomes of planetary formation and evolution,
these two images also highlight what is special about Earth. There’s no
place like home.”
The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. JPL designed,
developed and assembled the Cassini orbiter and its two onboard
cameras. The Johns Hopkins University Applied Physics Laboratory in
Laurel, Md., designed and built MESSENGER under NASA’s Discovery
Program. NASA’s Marshall Space Flight Center in Huntsville, Ala., manages
the program for the agency’s Science Mission Directorate in Washington.
JPL and APL manage their respective missions for NASA. The California
Institute of Technology in Pasadena manages JPL for NASA.
To view the MESSENGER images, visit: http://go.nasa.gov/16Vnt5G.
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