Scientists believe they have found ice inside craters near Mercury's poles, a discovery they say could reveal more about the "building blocks" for life on other planets.
Though the small planet is closest to the sun, Mercury rotates nearly upright, meaning some areas on its poles never see sunlight.
Using evidence of reflectivity, surface temperatures and the presence of excess hydrogen gathered by NASA's Messenger spacecraft, the scientists have concluded there are deposits of ice and other organic material accumulated in dark areas of Mercury's surface.
Further study of the material could explain more about how life began on Earth, the scientists said at a NASA news conference broadcast online on Thursday.
The discovery comes after a wait of eight years since Messenger's 2004 launch.
"Messenger has revealed a very important chapter in the story of how water, ice and other volatile materials have been delivered to the inner planets, including Mercury," said Sean Solomon, a Columbia University scientist who is principal investigator of the Messenger mission.
"It's extraordinary that this chapter is so well-preserved on the planet closest to the sun."
The scientists published their research in three papers released on Thursday in the journal Science Express.
The scientists suspect the ice and organic material accumulated in the shadowed areas of craters after comets and asteroids delivered the material to Mercury's surface.
Despite the presence of ice, scientists don't expect to find water in liquid form - only as a solid or gas.
Still, James Green, director of NASA's planetary science division, said the finding "bodes well" for a continued search for water elsewhere in the solar system.
"No one is saying there is life on Mercury," Solomon said. "Mercury is becoming an object of astrobiological interest where it wasn't one before."