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How complicated can solar system sightseeing get? Check this out: NASA's Curiosity rover looks up from Mars, takes a picture of the planet Mercury moving across the sun, and then sends it back to Earth.
Mercury is just a fuzzy spot on the series of solar views, captured on June 3 by the telephoto camera that's part of Curiosity's Mastcam instrument. Nevertheless, it marks a couple of firsts: the first planetary transit of the sun observed from any planet other than Earth, and the first image of Mercury captured from Mars.
"This is a nod to the relevance of planetary transits to the history of astronomy on Earth," Texas A&M's Mark Lemmon, a member of the Mastcam science team, said in a NASA news release. "Observations of Venus transits were used to measure the size of the solar system, and Mercury transits were used to measure the size of the sun."
Two sunspots can also be seen in Curiosity's snapshots.
Curiosity and its six-wheeled predecessors have spotted marvelous things in Martian skies — including transits of the sun by Martian moons, some hot moon-on-moon action and sightings of Earth and its moon. Back in 2011, the European Space Agency's Mars Express orbiter watched the Martian moon Phobos cross in front of Jupiter.
There's more to come: Mars probes are being primed to watch for Comet Siding Spring zoom past the Red Planet in October. And in the year 2084, Mars will provide a vantage point for witnessing a rare Earth transit of the sun. Will any humans be there to see it, or will we still have to depend on robots to watch the transit for us? That sounds like a good topic for the comment section or the NBC News Science Facebook page.