Just in time for Christmas,scientists have confirmed a vast amount of ice at the north pole — on Mercury,the closest planet to the sun.
The findings are from NASA's Mercury-orbiting probe,Messenger, and the subject of three scientific papers released Thursday by thejournal Science.
The frozen water is located in regions of Mercury's northpole that always are in shadows, essentially impact craters. It's believed thesouth pole harbors ice as well, though there are no hard data to support it.Messenger orbits much closer to the north pole than the south.
"If you add it all up, you have on the order of 100billion to 1 trillion metric tons of ice," said David Lawrence of theApplied Physics Laboratory at Johns Hopkins University. "The uncertaintyon that number is just how deep it goes."
The ice is thought to be at least 1½ feet (0.3 meters) deep— and possibly as much as 65 feet (20 meters) deep.
There's enough polar ice at Mercury, in fact, to bury anarea the size of Washington, D.C., by two to 2½ miles (3.2 kilometers) deep,said Lawrence, the lead author of one of the papers.
"These are very exciting results," he added at anews conference.
For two decades, radar measurements taken from Earth havesuggested the presence of ice at Mercury's poles. Now scientists know for sure,thanks to Messenger, the first spacecraft to orbit Mercury.
The water almost certainly came from impacting comets, orpossibly asteroids. Ice is found at the surface, as well as buried under a darkmaterial.
Messenger was launched in 2004 and went into orbit 1½ yearsago around Mercury, where temperatures reach 800 degrees Fahrenheit (426Celsius). NASA hopes to continue observations well into next year.
Columbia University's Sean Solomon, principal scientist forMessenger, stressed that no one is suggesting that Mercury might hold evidenceof life, given the presence of water. But the latest findings may help explainhow water and other building blocks of life arrived elsewhere in the solarsystem, he said.
Mercury is becoming the subject of new interest "whereit wasn't much of one before," Solomon said.