Understanding Mercury

Scientists analyzing data sent back from the MESSENGER spacecraft's flyby of Mercury last year are developing a new picture of the tiny planet.

Historically, astronomers have seen Mercury as a dead world, akin to Earth's Moon. The emerging picture, however, is putting Mercury closer to Mars. Volcanism has played a substantial role in shaping the surfaces of both worlds-- a surprise in Mercury's case. Astronomers had assumed impacts would be a dominant factor.

That's not to say there haven't been impacts. MESSENGER, indeed, found a 430 mile wide crater-- that on a world having well less than half the diameter of Earth. Interestingly, at the same time scientists acknowledged volcanism has played a major role on Mercury, they also said the floor of the roughly 3.9 billion year old crater, named Rembrandt, seems to be relatively untouched by volcanism. Clearly, we still have much to learn.