Mercury Got Smaller Still

Cooling effect erased up to one mile of the planet's diameter By: Gabriel Gache, Science News Editor Mercury is the smallest planet in the solar system, but one thing is certain: it wasn't always this small. At least, that's what the data collected by NASA's MESSENGER spacecraft during the beginning of this year reveals. In the early history of the solar system, when Mercury was much warmer than it is today, it could have had a diameter bigger by at least 1.6 kilometers. Now, scientists say that the same cooling effect which is thought responsible for the shrinking of Mercury can account for its mysterious magnetic field. "Cooling of the planet's core not only fueled the magnetic dynamo, it also led to contraction of the entire planet. And the data from the flyby indicate that the total contraction is at least one-third... [read full story]