The planet Mercury is seven kilometres smaller now than it was when it first formed four billion years ago.
The closest planet to the sun has cooled over time with its surface cracking and wrinkling, a phenomenon first noted when the Mariner 10 probe passed the planet in the 1970s.
But images from NASA's Messenger probe have allowed researchers to offer up more accurate estimates for the rate of contraction, and they now report it is shrinking more than previously believed.
The Mariner probe photographed about 45 per cent of Mercury's surface when it flew past in 1974 and 1975.
Those pictures showed long scars in the surface where rock had been forced upwards by the shrinking body of the planet.
From these pictures, which show the ridges running for hundreds of kilometres and separating terrains that are at times thousands of feet apart in height, experts calculated that Mercury had shrunk by between one and three kilometres over the course of its existence.
But those results were at odds with studies suggesting a cooling object like Mercury should have contracted much more.
Since entering the planet's orbit in 2011 Messenger has photographed 100 per cent of Mercury's surface and allowed far more detailed examination of the rocky features, known as lobate scarps, leading to a change in the estimated reduction in radius to seven kilometres.
Dr Paul Byrne, the lead author of the new paper, said, "Some of these lobate scarps are enormous.
There's a structure called Enterprise Rupes in the southern hemisphere that is a single scarp system.
It's 1,000 kilometres long and in places has three kilometres of relief. Imagine standing in front of it.
It's Mercury's version of a mountain belt. It utterly dominates the topography and it is astounding given the diminutive size of Mercury."
WENN.com
source: newshub archive
