Cassini spacecraft set to capture "pale blue dot" of Earth

In this computer simulation, Earth can be seen where it will appear in a photo mosaic that will be shot by NASA's Cassini spacecraft as it flies behind Saturn on Friday. Earth, some 898 million miles away, will cover a single pixel in the photo.

NASA's Cassini spacecraft is poised to snap a dramatic portrait of Earth Friday, capturing a mosaic showing humanity's home in space as a pinprick of light just to one side of Saturn's spectacular rings.

Flying in Saturn's shadow as it loops behind the ringed world, Cassini's cameras will take a series of photos that will be assembled into a mosaic spanning the width of the gigantic ring system and, in the process, capturing distant Earth and its moon some 898 million miles away.

A similar mosaic was assembled in 2006, but the picture was set up for research and did not show the planet and its rings in natural color. This time around, Cassini will capture a view intended from the start for public consumption, one that will show Saturn and Earth as they would appear to an astronaut looking on from Saturn's far side.


The Voyager photo was taken at the request of Carl Sagan, who marveled at the "pale blue dot" that was Earth.


Most of the western hemisphere will be facing Saturn Friday afternoon when the Cassini spacecraft snaps a picture from the far side of Saturn.

She wants people to step outside and wave at Cassini and to "think about where we are, think about life on planet Earth, how incredibly marvelous it is, think about your own existence, just have a moment of cosmic self awareness."



"The moon, you know, is very much fainter than the Earth so probably we'll have to boost its brightness," Porco said. "But we should, in the narrow angle camera, be able to see both.

"I'm really hoping it's kind of a knock-your-socks-off picture with the diffuse rings in it, Saturn and so on," she said.



In this 2006 Cassini image, Earth is barely visible just to one side of Saturn's rings. The picture was intended for research purposes but Friday's shot of Earth and Saturn will be optimized to show the scene in natural color.





Porco never gave up hopes for a second opportunity. Three years ago, she and her staff began studying Cassini's planned trajectory to look for potential photo opportunities, occasions when the spacecraft would be in eclipse behind Saturn and out of the glare of direct sunlight.

A blow up of the 2006 image showing Earth as seen from Saturn.

As it turned out, July 19 was a good choice, one that did not interfere with normal science operations, and NASA began publicizing the encounter last month, launching a "Wave at Saturn" campaign on its web site.

"Maybe I'm too starry eyed about all this, but I know this -- when I went around giving talks about Cassini and I end my talk on that September 2006 picture, it's a picture that draws gasps from people," Porco said.

"Regardless of how cynical people are, they look at that and they see Saturn and its rings in a way they've never seen them before, and then they see Earth in the distance. It just gets people. So I was just trying to tap into that, that powerful recognition that moves people, only do it this time in advance."

A passionate advocate of space exploration, Porco set up two web competitions on her Diamond Sky Productions site, inviting the public to submit music and photos that capture the moment of the cosmic encounter. A second website, called "The Day the Earth Smiled," provides additional details.

She plans to digitize the winning entries and beam them into deep space through a radio telescope as "kind of a long-distance call to our fellow galactic citizens."



"What I'm intending to do with this is make it a serious message a la the previous Drake and Sagan efforts, instruct the recipients of this message how to even read it, and encode important information about us, our planet and so on," Porco said of her "Message to the Milky Way."

One contest, called Earth Beheld, asks the public to "contribute one image that best represents planet Earth and could be understandable to an extraterrestrial recipient.

The other contest -- A Musical Celebration -- asks for compositions capturing the "spirit and significance of The Day the Earth Smiled."



  • William Harwood
