Studies by the Messenger spacecraft have shown that Mercury, the smallest planet in the Solar System, is shrinking. Scientists say the planet has contracted by about 1.5 kilometers in diameter over its history and believe the shrinkage is caused by the planet's cooling core.
Scientists believe the shrinkage is due to the planet's core slowly cooling.
Studies published in the journal Science show the same process also powers the planet's magnetic field, a topic long debated by scientists.
"Cooling of the planet's core not only fuelled the magnetic dynamo, it also led to contraction of the entire planet," said Principal Investigator Sean Solomon of the Carnegie Institution of Washington, US.
"And the data from the flyby indicate that the total contraction is at least one-third greater than we previously thought.