GRAIL Spacecraft: Celebrating New Year's From the Moon

Although workers on NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission may not be attending New Year's Eve parties this weekend, they aren't too disappointed.

A quarter of a million miles away, the mission's two small spacecraft will enter the moon's orbit to begin what promises to be one of the most detailed studies of its surface and gravity.

"Our team may not get to partake in a traditional New Year's celebration, but I expect seeing our two spacecraft safely in lunar orbit should give us all the excitement and feeling of euphoria anyone in this line of work would ever need," David Lehman, project manager for GRAIL at NASA's Jet Propulsion Laboratory in Pasadena, Calif., said in a statement.

The first of the two spacecraft is scheduled to arrive at the moon at 4:21 p.m. EST on Saturday, with the second arriving at 5:05 p.m. EST on Sunday. Both were launched in early September on the same United Launch Alliance Delta II rocket from Cape Canaveral, Fla.

By precisely measuring how the moon's gravity affects the distance between the two spacecraft as they orbit during the 82-day mission, researchers expect to better understand the origins of the moon, where humans may someday spend more than a few passing hours at a time. They also hope the $350 million mission will provide some insight into how the Earth and other rocky planets formed.

"I predict we are going to find something ... that is really, really going to surprise us and turn our understanding of how the Earth and other terrestrial planets formed on its ear," said Maria Zuber, the principal investigator with the mission, in an August news briefing.