This astonishing photo taken by NASA’s Cassini space probe captures the fragility of our home planet Earth beneath the rings of giant Saturn.
Cassini’s cameras were turned to look back into the solar system and record our blue world with its partner in space, the Moon, on 19 July. It wasn’t the only probe to do so because Messenger took its own photo the same day as it orbited inner planet Mercury.
From a distance of 1.44 billion km (nearly 900 million miles) Cassini saw Earth as a tiny blob, evoking memories of what legendary cosmic populariser Carl Sagan described as the “Pale Blue Dot” when Voyager 1 took a similar image in 1990. It is only the third time our planet has been pictured from the outer solar system.
This latest picture was the first for which the world was given advance notice. The moment it was taken was celebrated with an event called The Day The Earth Smiled when space enthusiasts and others around the world turned to wave at Saturn in the sky.
In fact more than one image was taken. Our stunning main image was taken by Cassini’s wide-angle camera and is a composite of three pictures taken through colour filters. But another narrow-angle camera was able to zoom in on the Earth to show the Moon too.
In the wide-field image, Saturn appears mainly in silhouette as if faces the Sun, with just a bright fringe along its limb. The main rings with the gaps between them are quite distinct. And the blue-white blurry band towards the bottom of the image is another ring – the E ring – lying closer to the camera.
Cassini imagine lead scientist Dr Carolyn Porco, of the Space Science Institute, in Colorado, told this writer via Twitter: “The E ring!!! Caused by Enceladus’ geysers. Could be dead microbes in that thing…”
If that sounds dramatic, space scientists see it as a real possibility. The E ring is fed by sprays of salty water ice from within Saturn’s moon Enceladus. There appears to be a large ocean beneath its surface, kept warm by Saturn’s tidal forces, and scientists speculate that it could be home to simple life.
Of The Day The Earth Smiled, Dr Porco said: “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. The whole event underscores for me our ‘coming of age’ as planetary explorers.”
Linda Spilker, Cassini project scientist, based at NASA’s Jet Propulsion Laboratory, said: “Cassini’s picture reminds us how tiny our home planet is in the vastness of space, but also testifies to the ingenuity of the citizens of this tiny planet to be able to send a robotic spacecraft so far away from home to take a picture of Earth and study a distant world like Saturn.”
The Cassini–Huygens mission is a joint project with ESA and Italy’s ASI space agency.
Messenger, which is the first probe to orbit Mercury, took a black-and-white image of the Earth and Moon from a distance of 98 million km (61 million miles). Each body is less than a pixel in size, but appear very large and distorted in shape because they are overexposed.
Messenger’s Principal Investigator Sean Solomon, of Columbia University, New York, said: “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.
“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.”
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