Mercury, the smallest planet in the solar system, may be shrinking at a faster rate than previously believed, according to new research. Measuring just over 1,516 miles (2,440 kilometers) in radius, Mercury formed approximately 4.5 billion years ago during the turbulent early days of the solar system. Over time, its metallic core has cooled and contracted, leading to observable surface changes such as ridges and valleys caused by the planet’s gradual shrinking.

Earlier estimates suggested that Mercury had contracted by only a few miles since its formation. However, a study published recently in Geophysical Research Letters indicates that the planet may have shrunk by as much as 14.5 miles (23.3 kilometers), which is nearly 1 percent of its current radius—around 10 to 30 percent faster than prior assessments. This revised figure provides new insights into the thermal and geological evolution of Mercury and other terrestrial planets.

The research was led by planetary scientist Gaku Nishiyama from the German Aerospace Center Institute of Space Research. His team analyzed surface features captured during NASA’s 2004 Messenger spacecraft flyby, as well as recent digital topographic models. By examining wrinkles on Mercury’s surface—structures such as ridges and valleys—they inferred the extent of the planet’s contraction.

One challenge the researchers faced was distinguishing these shrinkage-related features from other surface markings obscured by lava flows and impact debris. These complexities complicate the task of accurately interpreting Mercury’s surface from nearly 97 million miles away. Dr. Nishiyama noted that relying solely on visible topographies limits precise estimations, and future missions or additional data will be necessary to refine shrinkage measurements further.

This study also places Mercury’s contraction in context with other celestial bodies like the Moon and Mars, which are known to be shrinking as well. However, Mercury’s large metallic core allows for greater contraction compared to these bodies, making its case unique. The updated shrinkage rates contribute to a broader understanding of planetary formation and the long-term cooling and geological processes that shape rocky planets.