NASA's New Year's Resolution: Have 2 Gravity Probes Orbit the Moon

An artist's depiction of NASA's Grail-A spacecraft arriving in lunar orbit on Dec. 31, 2011.
An artist's depiction of NASA's Grail-A spacecraft arriving in lunar orbit on Dec. 31, 2011. (Image credit: NASA/JPL-Caltech)

A NASA spacecraft is circling the moon, with another closing in today (Jan. 1) in back-to-back lunar arrivals to ring in the New Year at Earth's nearest neighbor.

The two washing machine-sized spacecraft began their tag-team lunar arrival on Saturday afternoon (Dec. 31) with the New Year's Eve approach by one of the probes. If all goes well, the second probe will fire its rocket engine today at 5:05 p.m. EST (2205 GMT) in a 39-minute maneuver to enter lunar orbit.

The twin Gravity Recovery And Interior Laboratory (Grail) spacecraft, known as Grail-A and Grail-B, are designed to map the lunar gravity field in unprecedented detail in order to glean clues about the moon's interior structure, composition and formation. The $496 million moon mission is expected to begin in earnest in March and last about 82 days.

"My resolution for the new year is to unlock lunar mysteries and understand how the moon, Earth and other rocky planets evolved," said Grail principal investigator Maria Zuber, of the Massachusetts Institute of Technology in Cambridge, in a statement. "Now, with Grail-A successfully placed in orbit around the moon, we are one step closer to achieving that goal."

Currently, the Grail-A probe is circling the moon in an 11 1/2-hour orbit that approaches within 56 miles (90 kilometers) of the lunar surface at its closest point and extends out to 5,167 miles (8,363 km) at the farthest point, NASA officials said.

As of Saturday afternoon, the Grail-B spacecraft was about 30,018 miles (48,309 km) from the moon and closing at a rate of 896 mph (1,442 kph), according to a mission update. A team of 40 scientists will be watching over the probe's lunar orbital arrival to make sure everything goes as planned.

"With Grail-A in lunar orbit we are halfway home," Grail project manager David Lehman, of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., said in a statement Saturday. "Tomorrow may be New Year's everywhere else, but it's another work day around the moon and here at JPL for the Grail team."

NASA launched the Grail spacecraft on Sept. 10 and the probes took a circuitous route to the moon, traveling nearly 2.5 million miles (4 million km) — about 30 times the actual Earth-moon distance. The meandering path allowed NASA to spend extra time testing the Grail probes' health, mission managers have said.

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Tariq Malik

Tariq is the Editor-in-Chief of and joined the team in 2001, first as an intern and staff writer, and later as an editor. He covers human spaceflight, exploration and space science, as well as skywatching and entertainment. He became's Managing Editor in 2009 and Editor-in-Chief in 2019. Before joining, Tariq was a staff reporter for The Los Angeles Times covering education and city beats in La Habra, Fullerton and Huntington Beach. In October 2022, Tariq received the Harry Kolcum Award for excellence in space reporting from the National Space Club Florida Committee. He is also an Eagle Scout (yes, he has the Space Exploration merit badge) and went to Space Camp four times as a kid and a fifth time as an adult. He has journalism degrees from the University of Southern California and New York University. You can find Tariq at and as the co-host to the This Week In Space podcast with space historian Rod Pyle on the TWiT network. To see his latest project, you can follow Tariq on Twitter @tariqjmalik.