Mercury

Why We Study Mercury

Mercury doesn't always receive a lot of attention. The innermost planet to the Sun is smaller than both Jupiter’s moon Ganymede and Saturn’s moon Titan. It has been overshadowed by worlds like Mars that may have once harbored life, and planets that are solar systems unto themselves like Jupiter and Saturn.

Mercury is a world of extremes. Its surface appears old, cratered, and undisturbed by recent geologic activity. Yet it has a magnetic field, which is normally caused by a molten core that should, in turn, cause surface changes. Thanks to the nearby Sun, Mercury’s surface temperatures reach 430 degrees Celsius (800 degrees Fahrenheit)—yet like our Moon, water ice exists inside permanently shadowed craters at the poles.

Mercury is particularly interesting to scientists who study exoplanets, planets that orbit other stars. Thousands of known exoplanets orbit extremely close to their stars. By studying Mercury right here in our backyard, we can better understand what these close-orbiting worlds might be like.

Mercury’s core makes up 85 percent of the planet’s volume—much more than Earth’s, which makes up just 15 percent. Scientists aren't sure why, and the answer may help us understand the possibilities for different types of planets and how our solar system evolved.