Mercury is as cold as ice.

Indeed, Mercury, the closest planet to the Sun, possesses a lot of ice — 100 billion to one trillion tons — scientists working with NASA’s Messenger spacecraft reported on Thursday.

Sean C. Solomon, the principal investigator for Messenger, said there was enough ice there to encase Washington, D.C., in a frozen block two and a half miles deep.

That is a counterintuitive discovery for a place that also ranks among the hottest in the solar system. At noon at the equator on Mercury, the temperature can hit 800 degrees Fahrenheit.

But near Mercury’s poles, deep within craters where the Sun never shines, temperatures dip to as cold as minus 370.