Despite searing daytime temperatures, Mercury, the planet closest to the sun, has ice and frozen organic materials inside permanently shadowed craters in its north pole, Nasa scientists say.
Earth-based telescopes have been compiling evidence of ice on Mercury for 20 years, but the finding of organics was a surprise, say researchers with Nasa's Messenger spacecraft, the first probe to orbit Mercury.
Both ice and organic materials, which are similar to tar or coal, were believed to have been delivered millions of years ago by comets and asteroids crashing into the planet.
"It's not something we expected to see, but then of course you realise it kind of makes sense because we see this in other places", such as icy bodies in the outer solar system and in the nuclei of comets, the planetary scientist David Paige of the University of California, Los Angeles, told Reuters.
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