A NASA Discovery mission to conduct the first orbital study of the innermost planet
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Before the Mariner 10 mission in 1974, Mercury’s surface features were little more than a blur to Earth-bound observers. Mariner 10 made the first flyby of Mercury on March 29, 1974 at a distance of about 700 kilometers. Its high-resolution photographs of about 50% of Mercury’s surface allowed scientists to view the planet close-up. On its surface, Mercury closely resembles our Moon. Impact craters cover the majority of the planet but unlike the Moon, Mercury’s cratered upland regions are covered with large areas of smooth plains. The most distinguishing features on Mercury’s surface are scarps, or long cliffs. These wind across Mercury’s surface for tens to hundreds of kilometers and range from 100 meters to over 1.5 kilometers in height. What makes these cliffs so unique is that no other planet or moon features such a vast number of them. They are thought to be thrust faults created when the planet, as it cooled, shrunk by up to 4 km in diameter.

The largest surface feature photographed by the Mariner 10 mission is the Caloris basin. This is a multi-ringed (resembling a bull’s-eye) impact basin 1,340 km across - almost 1⁄4 of the full diameter of the planet. The basin includes a series of circular mountain ranges up to 3 km in height - the tallest mountains on Mercury. Caloris is thought to have been produced when a very large asteroid collided with the planet about 4 billion years ago. The massive impact sent seismic waves echoing through the planet. Coming to a focus on the opposite side of Mercury, these intense waves created there a region of hilly and broken terrain.

Explore Mercury’s Surface and learn about scarps, the coloris basin and more [HERE] by selecting the Surface Interactive.

Learn about the Atmosphere of Mercury