Signs of volcanic activity on Mercury

WASHINGTON: The US space probe MESSENGER's second fly-by of the planet Mercury in October 2008 revealed the solar system's smallest planet to be far more active than previously thought, four studies said on Thursday.

The MESSENGER (MErcury Surface, Space ENvironment, GEochemistry and Ranging) probe's cameras took more than 1,200 images of the surface, including details of a mammoth well-preserved 692-kilometer impact basin that shows signs of a volcanic past.

The so-called Rembrandt basin is the first such geological feature observed on Mercury where the ground is well exposed and not covered by a thick layer of volcanic ash, like most of the planet's other features.