The measurements, made with NASA's Mercury-orbiting

The measurements, made with NASA's Mercury-orbiting MESSENGER spacecraft, match computer model predictions, which scientists use to determine the planet's
inner composition, chemistry and structure.

"An awful lot of a planet's processes are driven by its heat loss - that's a primary thing that drives a planet's evolution," Byrne said. "We didn't set out
to prove the models right, but it turns out this number is exactly what the models have been predicting for 40 years."

Previous maps of Mercury's surface map date back to the mid-1970s. NASA's Mariner 10 spacecraft made three flybys of the planet, imaging about 45 per cent of
its surface.

That data indicated Mercury had lost 1.9 to 4.8km  in diameter, a finding that clashed with scientists' heat dissipation models for the planet.In addition to
learning more about how Mercury evolved, the discovery has implications for assessing the compositions of planets beyond the solar system.

"It may be that Mercury is an archetypal example of what a planet does and how it behaves as it has cooled in time," Byrne said.

The research is published in the journal Nature Geoscience.

It won’t be nearly as much fun as eating candy bars, but a big study is being launched to see if pills containing the nutrients in dark chocolate can help
prevent heart attacks and strokes.