GRAIL Twins Enter Lunar Orbit — UPDATE

GRAIL Twins Enter Lunar Orbit — UPDATE

UPDATE: The two spacecraft entered lunar orbit as scheduled.

ORIGINAL STORY:  NASA’s twin GRAIL spacecraft will enter lunar orbit today and tomorrow, respectively.  The two identical spacecraft  — one following the other as they orbit the Moon — will map its gravity field and give scientists a better understanding of the Moon’s interior.

After decades of study, scientists still do not understand the origin of the Moon.   A new theory is that the Earth originally had two moons that “bumped” into each other, forming the Moon we have today.   The theory responds to observations of the near- and far-sides of the Moon, which are very different from each other.    Observations from GRAIL could help determine if the theory is correct.

The two spacecraft are currently dubbed GRAIL-A and GRAIL-B, but will receive new names once they enter orbit.   GRAIL-A is due to conduct its lunar orbit insertion burn beginning at 4:21 pm EST today, New Year’s Eve.  GRAIL-B will follow suit tomorrow, New Year’s Day, beginning at 5:05 pm EST.

Maria Zuber of MIT is the principal investigator on the GRAIL mission.

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