Mercury may be shrinking 30% faster than earlier estimates, study finds

Capecanaveral,UPDATED: Sep 11, 2026 05:28 IST

A new study has found that Mercury may be shrinking faster than scientists had earlier believed, with the planet's diameter possibly reducing by as much as 14 miles, or 23 km. Researchers said the shrinkage could be about 30 per cent greater than previous estimates, a notable change for a planet that is barely 3,000 miles, or 4,900 km, across.

The findings, published in the journal Geophysical Research Letters, suggest Mercury's battered and uneven surface may have hidden the full extent of the loss. The study comes a week after the linked European and Japanese BepiColombo spacecraft shed their cruising platform and moved closer to Mercury ahead of entering orbit in November, when they are expected to split up for a more detailed survey.

Gaku Nishiyama, the study's lead author and a participant in the BepiColombo mission, said the spacecraft's laser instrument should help confirm how much Mercury is shrinking because of internal cooling. He added that the shrinkage could be even greater than what his team has estimated from measurements taken by NASA's Messenger spacecraft in the 2010s. Before Messenger, only one other spacecraft had visited Mercury: NASA's Mariner 10 in the 1970s.

Mercury, the smallest and innermost planet in the solar system, has been shrinking since it formed 4.5 billion years ago. Scientists said its large hot iron core cools and contracts, along with the mantle and crust, pulling the surface tighter as the planet slowly becomes smaller.

Nishiyama and his team compared maps showing faults and other geological signs of contraction with newer maps of surface roughness. They found that the roughest areas showed fewer shrinkage wrinkles, suggesting that some of the missing wrinkles may be buried under debris thrown up by impact craters. After taking these hidden regions into account, the researchers said their revised estimate of Mercury's shrinkage could also help improve understanding of other worlds that are contracting.

"We are quite excited," Nishiyama said in an email, adding that it feels like "we are approaching the reality of Mercury's evolution". The study says Mercury may have shrunk more than earlier thought, with fresh observations from BepiColombo expected to provide a clearer picture.

With PTI Inputs

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