Does Mercury Have Ice on It?

Does Mercury Have Ice?

Yes — Mercury has confirmed water ice right now, sitting inside permanently shadowed craters near its north pole, where temperatures drop to around –280°F (–173°C), even as the sunlit ground outside reaches 800°F (427°C).

How Is Ice Possible on the Closest Planet to the Sun?

It sounds impossible. Mercury orbits just 36 million miles from the Sun — closer than any other planet — and its daytime surface is hot enough to melt lead. Yet NASA’s MESSENGER spacecraft confirmed beyond doubt that water ice exists there, locked inside polar craters that have never once seen sunlight.

The key is Mercury’s axial tilt: a fraction of a single degree, the smallest of any planet in the solar system. Because Mercury is essentially perfectly upright relative to its orbit, the Sun’s rays never reach the floors of craters near the poles. Those floors sit in permanent, eternal shadow. No sunlight in billions of years. No warmth. Just a cold so extreme that water ice deposited long ago has simply… stayed.

Prokofiev and Kandinsky: The Ice-Hosting Craters

The two craters most associated with Mercury’s ice are Prokofiev and Kandinsky, both located near the planet’s north pole.

Prokofiev crater is the largest confirmed ice-hosting crater on Mercury, stretching roughly 70 miles (112 km) across. Its floor has been perpetually shielded from the Sun. Kandinsky crater similarly sits in permanent shadow, its interior floor preserving ice that likely arrived billions of years ago.

These are not small features. They are vast, ancient scars — the result of massive impacts — whose geometry accidentally created some of the coldest, most stable real estate in the inner solar system.

How Did MESSENGER Confirm the Ice?

Ground-based radar observations had hinted at something unusual at Mercury’s poles as far back as the early 1990s — bright radar reflections that looked suspiciously like water ice. But confirmation required getting up close.

NASA’s MESSENGER spacecraft (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) orbited Mercury from 2011 to 2015, the first spacecraft ever to do so. Using neutron spectrometry, it detected the hydrogen signatures consistent with water ice concentrated in the permanently shadowed polar craters. The evidence was unambiguous. Scientists confirmed what radar had suggested for decades.

Where Did Mercury’s Ice Come From?

The leading explanation is cometary and asteroid delivery. Comets and water-rich asteroids have been bombarding the inner solar system for billions of years. When one strikes Mercury, it can deposit water molecules on the surface. On most of Mercury, that water is immediately vaporized by the Sun. But molecules that migrate toward the poles — through a process called cold trapping — can fall into permanently shadowed craters and freeze permanently.

The same catastrophic collisions that cratered and scarred Mercury’s surface may have also seeded it with water ice.

The Most Extreme Temperature Swing in the Solar System

Mercury holds a remarkable record: an ~1,100°F (600°C) temperature swing between its sunlit and shadowed regions — the most extreme of any world in the solar system. No other planet experiences such a violent contrast in such close proximity.

A crater rim baking at 800°F. A crater floor, just a short distance away in geological terms, preserving ancient ice at –280°F. Same planet. Same moment. It is one of the most dramatic demonstrations of how geometry — the angle of a crater wall, the tilt of a planet’s axis — can determine whether water survives or vanishes entirely.

Why It Matters

Water ice is considered one of the fundamental ingredients associated with life as we know it. Its confirmed presence on Mercury — the solar system’s most punishing world — is a reminder that water finds ways to persist in unexpected places. It also strengthens the scientific case that comets and asteroids have been distributing water across the solar system for billions of years, including, perhaps, to early Earth.