The MESSENGER spacecraft was launched in 2004 and spent seven years getting to Mercury; it's not all that easy dropping a probe down into the inner solar system. It swung by Mercury twice (not to mention the Earth once and Venus twice!) before finally settling into orbit in March 2011, and then beginning its scientific mission of analyzing the overheated world. Among the first pictures it took was this one, showing the crater named Debussy (after the composer). The crater is 80 km (50 miles) wide, but reaching much farther are those streaks called rays; collapsed plumes of ejected material when whatever hit Mercury hit Mercury. Many craters on the Moon show rays, and in some cases pictures of the two objects look very similar.

Since March, MESSENGER has taken huge amounts of data of the planet, increasing our knowledge of what makes it tick - and it's returned not just images but also laser altimetry data, spectroscopy, and mineralogical maps. Mercury isn't much like Earth at all, but sometimes it's the contrasts that aid our understanding. The planets in the solar system are a diverse lot, and it's only by studying all of them that we can come to understand the one we live on.

Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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