Mercury has shrunk by 'more than a mile'

London, July 7 : Studies by the Messenger spacecraft have shown that Mercury, which is the smallest planet in the solar system, has contracted by more than one mile (1.5km) in diameter over its history.

According to a report by BBC News, this new information was derived from a flyby of Mercury in January 2008 by the Messenger.

Scientists have suggested that the shrinkage is due to the planet's core slowly cooling.

Earlier studies 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," he added.

According to Dr Thomas Zurbuchen of the University of Michigan, "The Mercury magnetosphere is full of many ionic species, both atomic and molecular."

This magnetosphere is created by the planet's core, which accounts for 60% of the planet's mass.

As well as influencing the space around the planet, the core has had an immense influence on surface features.

"The dominant tectonic landforms on Mercury, including areas imaged for the first time by Messenger, are features called lobate scarps, huge cliffs that mark the tops of crustal faults that formed during the contraction of the surrounding area," explained Dr Solomon.

"They tell us how important the cooling core has been to the evolution of the surface," he added.

The Messenger (Mercury Surface, Space Environment, Geochemistry and Ranging) spacecraft passed within 200km (125 miles) of Mercury earlier this year.

It was the first time the planet had been viewed up close since Mariner 10's third and final fly-by in March 1975.

The flyby was one of three to be made by the craft as it prepares to enter into orbit around the solar system's smallest planet in 2011.

ANI