On 19 July 2013, the marvelous Cassini spacecraft will pause in its complicated orbital dance with Saturn and his moons to take an image of Earth silhouetted through the rings with it’s most high resolution camera. Reminiscent of Voyager 1’s iconic 1990 image “Pale Blue Dot”, the picture will show a pixel-sized Earth in natural colour to give a realistic view of how our home planet looks from over 1.4 billion kilometers away.
Unusually, there doesn’t seem to be any specific science goal to this picture. Rather, the mission team seem to be doing this partly to create an image for fans of space exploration to hang up on their bedroom walls and partly because it’s a rare opportunity to do something incredibly cool.
“While Earth will be only about a pixel in size from Cassini’s vantage point 898 million (1.44 billion kilometers) away, the team is looking forward to giving the world a chance to see what their home looks like from Saturn,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif. “We hope you’ll join us in waving at Saturn from Earth, so we can commemorate this special opportunity.”
Cassini’s camera will begin photographing Earth at 21:27 UTC (11:27pm SAST), shortly before Saturn sets below the horizon for South African viewers, and the exposure will last 15 minutes. So if you see people standing outside in the dead of night, braving the winter’s chill to wave frantically at the western horizon, they’re probably just astronomers taking Dr Spilker up on her challenge!
Of course, expensive missions like Cassini can’t justify the delicate maneuvering and careful planning needed to do fun things like this without slipping in some real science at the same time. Earth is so close to the Sun from Saturn’s point of view that it’s normally not possible to point one of Cassini’s sensitive cameras at it without damaging the sensitive sensors, so to line up the shot they will be hiding in Saturn’s shadow.
This means that the Rings of Saturn will be strongly back-lit, revealing subtle features normally too faint to detect.
“Looking back towards the sun through the rings highlights the tiniest of ring particles, whose width is comparable to the thickness of hair and which are difficult to see from ground-based telescopes,” said Matt Hedman, a Cassini science team member based at Cornell University in Ithaca, N.Y., and a member of the rings working group. “We’re particularly interested in seeing the structures within Saturn’s dusty E ring, which is sculpted by the activity of the geysers on the moon Enceladus, Saturn’s magnetic field and even solar radiation pressure.”
In other words, the spectacular image we can expect to see in a little over a month will also reveal some quite spectacular science!