The innermost planet, our little sibling Mercury might be very similar to other terrestrial planets in the solar family, but as Nasa’s Messenger probe finds, it has many secrets of its own.
Its heavily cratered surface is dotted with irregularly shaped depressions, many of which have bright blue interiors and halos. These landforms seem exclusive to Mercury’s geology, unheard of on earth; similar features observed on Mars are attributed to the evaporating carbon dioxide ice, which is alien to Mercury.
“The science team adopted the term ‘hollows’ for these features to distinguish them from other types of pits that are found on Mercury,” said David T. Blewett, planetary scientist working on the images captured by Messenger.
In one of the seven Mercury themed papers published in the journal Science, Blewett and his team explain how these hollows seem to be growing as they cover more ground, suggesting that Mercury is geologically active.
A traditional view of Mercury was derived from its clear high density compared to other planets, which was assumed to be a result of its exposure to very high heat in its early days. Data from Messenger’s spectrometer identifies abundance of sulphur and potassium, both of which vaporise easily, thus negating previous assumptions.
“Theorists need to go back to the drawing board on Mercury’s formation,” remarked the lead author of one of the papers, Carnegie’s Larry Nittler. “Most previous ideas about Mercury’s chemistry are inconsistent with what we have actually measured on the planet’s surface.”