Ice? ... Mercury's north pole.

Ice? ... Mercury's north polar region may hold frozen water. Photo: NASA

Scientists believe they have found ice inside craters near Mercury's poles, a discovery they say could reveal more about the "building blocks" of 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 that 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. The discovery comes after a wait of eight years since Messenger's 2004 launch, and over the past year as the spacecraft circled Mercury.

A mosaic of Messenger's images of Mercury's north polar region.

A mosaic of Messenger's images of Mercury's north polar region. Photo: NASA

"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 C. 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."

Much of the research was based at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, and the NASA Goddard Space Flight Centre in Greenbelt, Maryland. The scientists published their research in three papers released on Thursday in the journal Science Express.

Instruments aboard Messenger discovered deep deposits rich in hydrogen using spectroscopy, which views radiative energy outside of the visible spectrum. Scientists then used a laser altimeter to make detailed maps of Mercury's topography, much like ships use sonar to detect variation in the ocean floor, which corroborated evidence of irregular deposits.

The scientists said the evidence came together to support their hypothesis of ice deposits.

"They're difficult, challenging results, and to have them all come together in this way is kind of like a key — you get the right key and turn the lock, and the door opens," said David J. Lawrence of the Hopkins lab, who was a participating scientist in the Messenger mission. "All of the results are pointing to the same place."

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.

But despite the presence of ice, scientists don't expect to find water in liquid form — only as a solid or gas. Still, James L. 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."

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