Tuesday, February 16, 2010

Carl Sagan's Voyager is 20 Years old


Image credit: NASA/JPL.
These six narrow-angle color images were made from the first ever 'portrait' of the solar system taken by Voyager 1, which was more than 4 billion miles from Earth and about 32 degrees above the ecliptic.

Twenty years ago on February 14, NASA's Voyager 1 spacecraft had sailed beyond the outermost planet in our solar system and turned its camera inward to snap a series of final images that would be its parting valentine to the string of planets it called home.

Mercury was too close to the sun to see, Mars showed only a thin crescent of sunlight, and Pluto was too dim, but Voyager was able to capture cameos of Neptune, Uranus, Saturn, Jupiter, Earth and Venus from its unique vantage point.

These images, later arranged in a large-scale mosaic, make up the only family portrait of our planets arrayed about the sun.

The Apollo missions in the 1960s and 70s had already altered our perspective of Earth by returning images of our home planet from the moon, but Voyager was providing a completely new perspective, said Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena.

"It captured the Earth as a speck of light in the vastness of the solar system, which is our local neighborhood in the Milky Way galaxy, in a universe replete with galaxies," Stone said.

In the years since the twin Voyager spacecraft were launched in 1977, they had already sent back breathtaking, groundbreaking pictures of the gas giants Jupiter, Saturn, Uranus and Neptune. It took Voyager 1 more than 12 years to reach the place where it took the group portrait, 6 billion kilometers (almost 4 billion miles) away from the sun.

The imaging team started snapping images of the outer planets first because they were worried that pointing the camera near the sun would blind it and prevent more picture-taking.

Candy Hansen, a planetary scientist based at NASA's Jet Propulsion Laboratory in Pasadena, Calif., who worked with the Voyager imaging team at the time, remembers combing through the images and finally finding the image of Earth. She had seen so many pictures over the years that she could distinguish dust on the lens from the black dots imprinted on the lens for geometric correction.

There was our planet, a bright speck sitting in a kind of spotlight of sunlight scattered by the camera. Hansen still gets chills thinking about it.

"I was struck by how special Earth was, as I saw it shining in a ray of sunlight," she said. "It also made me think about how vulnerable our tiny planet is."

This was the image that inspired Carl Sagan, the the Voyager imaging team member who had suggested taking this portrait, to call our home planet "a pale blue dot."

As he wrote in a book by that name, "That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. ... There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world."

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