On Friday, July 19, Saturn won't be the only planet that will get photobombed by Earth; the MESSENGER spacecraft orbiting Mercury will also be taking pictures in our direction, capturing a few faint glimpses of our planet from 60 million miles away.
If you haven't heard, Cassini will be acquiring images of Saturn in eclipse on Friday, July 19. The geometry of the spacecraft's orientation will not only allow it to take some fantastic pictures of the ringed planet silhouetted against the sun, but also capture Earth in the shot as well - a tiny "pale blue dot" positioned just outside the rings.
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Although a similarly spectacular image has been made by Cassini before in 2006 (shown above, right), Friday will be the first time a photo of our planet will be taken from 900 million miles away with prior public notice... and thus the world has been cordially invited to "smile at Saturn" as Cassini begins acquiring images at 5:27 p.m. EDT (21:27 UTC) on July 19.
But if you're a little camera shy, don't worry - you'll have a chance to perfect your long-distance grin when MESSENGER starts shooting at 7:49, 8:38, and 9:41 a.m. EDT on the same day.
(Have prior engagements? It's OK - MESSENGER will also be capturing images on Saturday at the same times.)
Of course, MESSENGER isn't out there just to see what Earth looks like from .65 AU. It's on the hunt for natural satellites around Mercury, any possible moons present around the innermost planet that, for some reason, have not yet been detected.
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"We don't know why Mercury does not have a moon," said William Merline, of the Southwest Research Institute (SwRI) in Boulder, Colorado. "It may have been just unfortunate in not having the right history, in terms of collisions," Merline continued. "Or it may at one time have had a moon in an orbital trajectory that was disrupted by the strong gravitational pull of the Sun... but these possibilities are only speculations, based on theoretical ideas. To complete the picture, we must search for the existence of satellites to validate any of these suggestions."
MESSENGER's images - which, even if they don't show any moons, will at least include a distant world called Earth - will be released next week. They might not be as grand as what Cassini will be getting, with an enormous eclipsed Saturn hogging the lens, but they will be a look at our planet from well over halfway to the sun - and a reminder that we reside in quite a special place in the solar system between two very different worlds.
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"The Saturn system and the innermost planet are two very different outcomes of planetary formation and evolution, so these two sets of images also prompt a sustained appreciation of the special attributes of Earth," said MESSENGER Principal Investigator Sean Solomon of Columbia University. "There's no place like home."
Read more on the MESSENGER mission site here, and learn more about the Cassini mission here.
Image (top): Left: MESSENGER image of Earth and the moon captured in May 2010 (NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington). Right: Cassini image of the Earth captured in September 2006 (NASA/JPL/Space Science Institute)