Of all the planets in our solar system, Mercury might be the most underrated. It doesn’t have fancy swirling clouds or rings or plumes. It doesn’t even have an atmosphere. This little rocky body does have a history of volcanism, though, and even has water ice in its craters. Mercury is also locked into a special resonance with Jupiter (think of it like a billion year old dance partner), and there’s a chance many millions of years from now, that Mercury will lose its balance and get flung out of the solar system and maybe take Mars out on its way.

Just this week, our innermost planet got its moment of glory, when it executed a rare transit, passing in front of the sun in just the right alignment so people on Earth could view it. It won’t transit again until 2032. Only two spacecraft have ever visited l’il Mercury: Mariner 10 in 1974 and 1975 and NASA’s Messenger mission which orbited Mercury from 2011 to 2015 when it was deorbited and crashed into the surface. This week we’re going to get a bit more familiar with the solar system’s innermost world.

If you take a look at the bottom left corner of this image of our sun, you’ll see a tiny black dot. Say hello to Mercury! On Monday, November 11, it began to cross between earth and the sun for the first time in several years. (Sure it looks especially small here but everything looks tiny next to the sun.)Photograph: Bill Ingalls/NASA
When NASA’s MESSENGER mission was in orbit around Mercury, it took photos of the planet in unprecedented detail, including this photo of the rim of the Rembrant basin. At 445 miles across, Rembrant is the largest basin on the surface, and that long seam running down the center of the image is a feature of plate tectonics.NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
The bright crater at the top of the image is called Dominici crater. Whatever struck the surface hit it hard enough to send ejecta material out across the planet, revealing the volcanic remnants and lighter material below. This entire basin has been filled in by lava from volcanoes, so meteorite strikes like these that stir up dirt and rocks can help scientists get some clues about what sorts of materials are below the surface.NASA Goddard
This false color image of the Caloris basin shows old lava in orange and material that has been stirred up by meteorite strikes in deeper purples. Scientists on the MESSENGER team planned this photo for when the sun and the spacecraft were directly overhead. Talk about using a natural light source to get your shot: The brightness of the sun meant that the instruments and camera on MESSENGER were able to collect clear, detailed data.NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
This is MESSENGER, our spacecraft du jour. The planet Mercury is named after the Greek messenger god, but NASA rarely does anything that is not also an acronym. MESSENGER stands for MErcury Surface, Space ENvironment, GEochemistry and Ranging. During its four years in orbit around Mercury not only did MESSENGER discover evidence of ancient volcanism on Mercury, but it found water ice in the craters as well.KSC

While you wait for the next Mercury transit, take a look at the rest of the collection of space photos here.

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