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A Martian moon slips by Jupiter

ESA / DLR / FU Berlin (G. Neukum)

Three frames from the series of 104 taken by Mars Express during the Phobos–Jupiter conjunction on 1 June 2011.

Alignments of planets, moons and stars as seen from Earth always get us excited. This close-up view of the Martian moon Phobos lined up with Jupiter ups the ante – it was seen by a spacecraft orbiting Mars.


Phobos is only 23 kilometers wide, whereas Jupiter is 142,000 kilometers across, but at the moment of the alignment on June 1, the European Space Agency's Mars Express orbiter was only 11,389 kilometers away from the lumpy moon. Jupiter was a further 529 million kilometers away.

The High Resolution Stereo Camera on Mars Express was kept fixed on Jupiter for the conjunction, ensuring that the planet remained static in the frame. The operation returned a total of 104 images over a period of 68 seconds, all of them taken using the camera’s super-resolution channel.

These images have been stitched together as a movie, seen below.

On June 1 2001, Mars express watched as Phobos (the inner and larger of Mars' two moons) slipped past distant Jupiter.

Beyond the cool factor of the chance alignment, the observations are helping astronomers refine their knowledge about the orbit of Phobos, which varies with time because of its small mass and extreme proximity to Mars, the Planetary Society's Emily Lakdawalla explains.

Mars Express is studying Phobos to help out the planned Russian Phobos-Grunt mission to land a spacecraft on the moon and snag a sample for return to Earth, which is due for launch in November.

More on Phobos:


John Roach is a contributing writer for msnbc.com. Connect with the Cosmic Log community by hitting the "like" button on the Cosmic Log Facebook page or following msnbc.com's science editor, Alan Boyle, on Twitter (@b0yle).