Both of NASA’s lunar probes successfully entered orbit around the moon over New Year's weekend as researchers prepare the craft to collect detailed gravitational data that will aid in gaining unprecedented understanding about the development of the moon and other planets in the solar system.

Probe GRAIL-A entered orbit by 6 p.m. on Saturday and GRAIL-B entered orbit on Sunday by 5 p.m. EST, NASA said. GRAIL stands for Gravity Recovery And Interior Laboratory. The first lunar probe, GRAIL-A, was in orbit by 6 p.m. EST in nearly 5,200 orbit that takes about 11.5 hours to complete, NASA said. The second probe entered at 5 p.m.

Each washing-machine-sized probe has an elliptical orbit with an orbital period of about 11.5 hours. After several days of engine burns, the spacecraft will accelerate to orbits just under two hours, NASA said.

The probes will eventually circle the moon in a nearly circular orbit about 34 miles above its surface and start collecting data in March.


The probes will transmit radio signals to each other, identifying the distance between them. The craft will fly over areas of greater and lesser gravity as they move past mountains, craters and masses hidden beneath the lunar surface, with the distance between the two probes changing slightly, NASA said.

That information will generate a high-resolution map of the moon’s gravitational field.

The data will provide information about what is below the moon’s surface and will increase knowledge about how it and other nearby planets in the solar system developed, according to NASA.

Each craft will get new names in January, after the conclusion of a middle-school student contest linked to an educational event associated with the probes that began in October, NASA said.

The mission is being managed from NASA’s Jet Propulsion Laboratory in Pasadena, Calif.