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Mercury Shrinking Faster Than Expected, New Study Suggests
Confirmed
In Short: Mercury is contracting at a faster rate than previously thought, according to a new study.
Mercury, the smallest and innermost planet in our solar system, is shrinking at a faster rate than scientists initially believed. According to a new study, the planet's diameter may have shrunk by up to 23 kilometers, or about 14 miles, since its formation 4.5 billion years ago. This finding, reported in the journal Geophysical Research Letters, suggests that Mercury may be losing more of its volume than previously estimated.
Planetary scientists have long known that Mercury's interior was cooling and contracting, but the new analysis indicates that the actual rate of this process has been underestimated. "This result suggests that Mercury has less light elements in the core, a larger inner core, and a higher initial temperature," explained Gaku Nishiyama, the study's lead author, in an interview with IFLScience.
The BepiColombo mission, a joint European and Japanese endeavor, is expected to provide more reliable information on Mercury's contraction features and surface roughness. The mission, which consists of two orbiters—the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO, or 'Mio')—is scheduled to enter orbit around Mercury in November 2026. Once in orbit, the BepiColombo Laser Altimeter (BELA) will capture Mercury's topography with greater resolution, potentially corroborating the findings and refining the estimates.
The new findings could have implications for understanding the evolution of other contracting worlds in our solar system and beyond. "If all the planets are roughly the same age, why is Mercury so wrinkly?" Nishiyama pondered. The answers to this question may help scientists better understand the processes that shape planets over time.
The BepiColombo mission, which began its journey to Mercury in 2018, is set to shed new light on the planet's geological history. After accounting for the obscured regions on Mercury's surface, the researchers provided a fresh take on the planet's shrinkage. "Only one other spacecraft has ever visited Mercury, NASA’s Mariner 10 in the 1970s," noted Nishiyama. With BepiColombo, scientists hope to gain a more comprehensive understanding of Mercury's past and present.
What's confirmed
- Mercury, the smallest and innermost planet in our solar system, is shrinking at a faster rate than scientists initially believed. According to a new study, the planet's diameter may have shrunk by up to 23 kilometers, or about 14 miles, since its formation 4.5 billion years ago. This finding, reported in the journal Geophysical Research Letters, suggests that Mercury may be losing more of its volume than previously estimated.
- Planetary scientists have long known that Mercury's interior was cooling and contracting, but the new analysis indicates that the actual rate of this process has been underestimated. "This result suggests that Mercury has less light elements in the core, a larger inner core, and a higher initial temperature," explained Gaku Nishiyama, the study's lead author, in an interview with IFLScience.
- The BepiColombo mission, a joint European and Japanese endeavor, is expected to provide more reliable information on Mercury's contraction features and surface roughness. The mission, which consists of two orbiters—the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO, or 'Mio')—is scheduled to enter orbit around Mercury in November 2026. Once in orbit, the BepiColombo Laser Altimeter (BELA) will capture Mercury's topography with greater resolution, potentially corroborating the findings and refining the estimates.
- The new findings could have implications for understanding the evolution of other contracting worlds in our solar system and beyond. "If all the planets are roughly the same age, why is Mercury so wrinkly?" Nishiyama pondered. The answers to this question may help scientists better understand the processes that shape planets over time.
- The BepiColombo mission, which began its journey to Mercury in 2018, is set to shed new light on the planet's geological history. After accounting for the obscured regions on Mercury's surface, the researchers provided a fresh take on the planet's shrinkage. "Only one other spacecraft has ever visited Mercury, NASA’s Mariner 10 in the 1970s," noted Nishiyama. With BepiColombo, scientists hope to gain a more comprehensive understanding of Mercury's past and present.
What's still developing
- The process is ongoing, and it might be happening faster than we thought.
- BepiColombo pictured zooming away from Mercury a few years back.
- With the transfer module gone, MPO and Mio orbiters are now headed toward orbit insertion at Mercury, with MPO powering the joined spacecraft until the two orbiters separate from each other.
- Professor Colombo was the first to see that an unsuspected resonance is responsible for Mercury’s habit of rotating on its axis three times for every two revolutions it makes around the Sun.
- He also suggested to NASA how to use a gravity-assist swing-by of Venus to place the Mariner 10 spacecraft in a solar orbit that would allow it to fly by Mercury three times in 1974-5.
- On September 3, 2026, mission controllers confirmed that the spacecraft’s Mercury Transfer Module (MTM) successfully separated from the rest of the stack, kicking off the mission’s ‘arrival phase.’ Confirmation came via two of ESA’s deep-space tracking antennas in Spain and Argentina, which picked up signals validating the separation.
- On Mercury, these signs of aging look like hills and ridges, called shortening structures, across its surface.
- Mercury’s rough surface, continually reshaped by debris hurled from impact craters, may have hidden the true extent of the loss, according to the researchers whose findings appear in the journal Geophysical Research Letters.