Shrinking planet Mercury is still getting smaller, new research finds

Planetary scientists have long known that Mercury has been shrinking for billions of years. The first evidence of Mercury's shrinkage came in 1974 when the Mariner 10 mission transmitted pictures of kilometres-high scarps snaking their way for hundreds of kilometres across the terrain. To accumulate the 2-3km of total shortening that can be measured across a typical scarp on Mercury would take hundreds of magnitude 9 "earthquakes", or more likely millions of smaller events, which could have been spread out over billions of years. Its lobate scarps are considerably smaller and less spectacular than those on Mercury, but on the Moon we know for sure that as well as being geologically recent, some are active today. Much smaller in scale than Mercury's grabens, similar logic applies to these boulder tracks: they would become erased from visibility after only a few million years, so they must be young.