Artist concept of GRAIL mission. Grail will fly twin spacecraft in tandem orbits around the moon for several months to measure its gravity field in unprecedented detail.?[Photo/Xinhua]

BEIJING - A NASA team will keep on monitoring its twin spacecraft orbiting the moon to find answers to what is inside the Earth’s companion and how it was formed, acording to media reports on Friday.

The USspace agency announced on Wednesday that the twin spacecraft to study the moon from crust to core are nearing their New Year's Eve and New Year's Day main-engine burns to be place in the lunar orbit.

Named Gravity Recovery and Interior Laboratory (GRAIL), the spacecraft are scheduled to be placed in orbit beginning at 4:21 p. m. EST (21:21 GMT) for GRAIL-A on Dec. 31, and 5:05 p.m. EST (22:05 GMT) on Jan. 1 for GRAIL-B.

The distance from the Earth to the moon is approximately 250,000 miles (402,336 kilometers), which took NASA's Apollo crews about three days to travel. Launched from Cape Canaveral Air Force Station Sept. 10, the GRAIL spacecraft are taking about 30 times that long and covering more than 2.5 million miles (4 million kilometers) to get there.

"This mission will rewrite the textbooks on the evolution of the moon," said Maria Zuber, GRAIL principal investigator from the Massachusetts Institute of Technology. "Our two spacecraft are operating so well during their journey that we have performed a full test of our science instrument and confirmed the performance required to meet our science objectives."

For the project, scientists will also focus on finding answers to whether the moon has the wracked body of a lost sibling body.

Base on evidence of the crash, if a sibling body wrack occurred, should be buried inside the moon, in the form of remnant radioactive materials, such as uranium and thorium, which would have been heated in the smash-up.

(Agencies)