Image of the Day: Phobos flyby

Last Sunday, the Mars Express orbiter made a ridiculously low flyby over the surface of Phobos, one of the moons of Mars. In astronomical terms, "ridiculously low" is just 28 miles. We're guessing that the only reason mission planners even allowed this little stunt was the Mars Express has been at Mars for over 10 years, which is a heck of a long time. And anyway, the poor thing is probably bored to tears just going in circles over and over.

What Mars Express was trying to figure out by doing the Phobos flyby is how massive, and how dense, the moon is. The spacecraft itself doesn't have any instruments that can measure this directly, but as it buzzes the moon, its orbit is going to be altered slightly by Phobos' gravity. Back on Earth, scientists can measure exactly what this alteration is, and from that, they can figure out what the mass of the moon is. Clever.

The bad news is that in order for this to work, Mars Express had to have its antenna pointed at Earth the whole time, which kept it from pointing its cameras at Phobos as it flew past. So, we're not going to get any ultra mega closeups, at least, not this time. But, earlier this week Mars Express made a 300 mile pass that it did have its instruments turned on for. The picture at the top of this article was taken from 4,200 miles away, so that should give you a sense of what we have to look forward to.

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ESA, via Discovery

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