Mercury May Be Shrinking Faster Than Thought, New Study Finds
A new study suggests Mercury's shrinkage may be 30% greater than previously believed, with BepiColombo expected to confirm the extent of the planet's contraction.
Mercury, the solar system's smallest and innermost planet, may be contracting more than scientists had estimated, according to a study published in the journal Geophysical Research Letters.
Researchers at the German Aerospace Center's Institute of Space Research reported that the planet's shrinkage could be about 30% greater than earlier calculations, amounting to a possible loss of up to 14 miles (23 kilometres) in diameter. The figure is notable for a world only about 3,000 miles (4,900 kilometres) across.
Mercury has been cooling and contracting since its formation roughly 4.5 billion years ago. Its unusually large iron core, along with the mantle and crust, has been shrinking as it loses heat, tightening the surface much like a girdle.
The study's lead author, Gaku Nishiyama, who is affiliated with Hokkaido University in Japan and is involved in an upcoming Mercury mission, said the team compared maps of faults and other geological signs of contraction with newer maps highlighting surface roughness. The roughest areas showed fewer shrinkage wrinkles, suggesting that impact debris thrown up from craters may have buried those features and obscured the true extent of the loss.
After accounting for these hidden regions, the researchers arrived at a revised estimate that could also inform the study of other contracting worlds. "We are quite excited," Nishiyama said in an email, adding that it felt like "we are approaching the reality of Mercury's evolution."
The findings rest on measurements from NASA's Messenger spacecraft, which studied Mercury in the 2010s. Only one other probe, NASA's Mariner 10 in the 1970s, has visited the planet.
The new estimate may soon be tested. The European-Japanese BepiColombo mission, a pair of linked spacecraft, shed its cruising platform last week and is advancing toward Mercury. The craft are expected to enter orbit around the planet in November before separating for a fuller survey. BepiColombo's laser instrument should help confirm how much Mercury is contracting as its interior cools, Nishiyama said.