Mercury's polar ice deposits, one of astronomy's strangest puzzles, may have formed in a single catastrophic event billions of years ago, according to new research. The planet closest to the sun hosts thick layers of frozen water at both poles, a counterintuitive discovery that has puzzled scientists since its detection in the 1990s.

A team of researchers modeled how a massive comet or asteroid impact could have delivered Mercury's water in one violent collision. The impact would have released enough energy to temporarily alter the planet's rotational dynamics and surface conditions, creating an environment where water could accumulate and freeze at the poles despite Mercury's proximity to solar radiation.

Mercury rotates extremely slowly, completing one rotation every 59 Earth days. This leisurely spin means the poles experience extended periods of darkness, allowing ice to persist in permanently shadowed craters despite surface temperatures elsewhere reaching 430 degrees Celsius. The new model suggests that a single impact event delivered most or all of the water now locked in these polar deposits.

The research challenges earlier theories proposing gradual water accumulation through multiple comet strikes over Mercury's history. Instead, the single-impact scenario explains the concentration and distribution of ice observed at Mercury's poles with greater efficiency.

Understanding Mercury's water has broader implications for planetary science. It reveals how rocky planets close to stars can retain volatile compounds and provides insights into the early solar system's dynamics. The findings also inform searches for habitability on exoplanets orbiting close to their host stars.

The study builds on decades of observations from NASA's Messenger spacecraft and Japan's BepiColombo mission, which continue mapping Mercury's surface composition. The researchers used computational models to simulate impact scenarios and their consequences for the planet's thermal and rotational properties.

While compelling, the single-impact hypothesis remains one possibility among several competing explanations. Future observations from BepiColombo may provide additional evidence supporting