Beyond the Dark Side of the Moon

Helen Hill | EAPS News
Wednesday, November 23, 2011

In October 1959 the Soviet Luna 3 satellite beamed back the first ever images of the dark side of the moon. Fifty-two years later a NASA satellite mission, launched on September 10th, 2011, aims to provide scientists with the first comprehensive images of the inside of the moon.

The Gravity Recovery And Interior Laboratory or GRAIL mission, directed by principal investigator Maria Zuber (the MIT Earle A. Griswold Professor of Geophysics and Planetary Science), marks the first time a woman has led a planetary spacecraft mission. The carefully choreographed venture uses twin spacecraft to precisely map the moon's gravitational field. It will answer longstanding questions about the moon's composition, internal structure and evolution. It will also shed light on how Earth and other rocky planets of the inner solar system formed.

Named one of "America's Best Leaders" by U.S. News and World Report in 2008, the Head of MIT's Earth, Atmospheric and Planetary Sciences Department's leading role in GRAIL provides her students not just with an unsurpassed foundation in planetary geophysics research but also with an exemplary model of world-class science leadership. As one of her students explained, "Maria Zuber is the reason I came [to MIT]. She's just so amazing at doing exactly the sorts of things I want to do in the future, combining engineering and science to really further our knowledge of the Solar System... of our Universe. I'm lucky to work with her."

The measurement technique GRAIL uses was pioneered by the joint U.S.-German Earth observing Gravity Recovery And Climate Experiment, or GRACE, mission launched in 2002. Unlike GRACE's satellites (which measure gravity changes related to the movement of mass within Earth, such as the melting of ice at the poles and changes in ocean circulation) GRAIL's satellites have been designed to measure differences in gravity caused by differences in the structure of the moon's constituent rock itself. As the satellite pair flies in a common orbit over areas of greater and lesser gravity (caused both by visible features such as mountains and craters but also by masses concealed beneath the lunar surface) they will move slightly toward and away from each other. On-board laser interferometry will precisely monitor the changes in their relative velocity; these variations can then be translated into a high-resolution map of the Moon's gravitational field, a map that can then be used to unlock remaining mysteries of how the moon formed.

At the time of writing, GRAIL's spacecraft are mid-way through their four-month journey, each spacecraft flying a similar but separate trajectory towards their destination. GRAIL-A is scheduled to enter lunar orbit December 31st with GRAIL-B joining it the following day. The pair will then spend about two months reshaping and merging their orbits until one spacecraft is following the other in the same low-altitude (~50km), near-circular, near-polar orbit, at which time formation-flying can begin. GRAIL’s 90-day scientific mapping mission will begin in March 2012 with data available for analysis from mid-2012.

Of the mission, Zuber says, “Technologically, it is blazing the trail for other planetary missions. Using dual spacecraft in tight-formation flight, doing precise timing and gravity measurement, you could envision future planetary missions to Europa [one of Jupiter’s moons] to map currents in its subsurface ocean; to Venus to map the circulation of its atmosphere; and to Mars to observe the seasonal carbon dioxide cycle between its atmosphere and its surface.”

Zuber's Group are an engaging bunch. Besides their obvious passion for planetary science, they clearly all have enormous respect and admiration for their mentor. They especially appreciate the value-added benefits of sharing a close relationship with the principal research scientist on a mission like GRAIL. At the post-launch party the students presented Maria with a cup engraved with the words "Let knowledge be plentiful, yet never quench our thirst". We look forward to that cup being filled with questions as well as answers as GRAIL-A and GRAIL-B begin reporting back to us.

Read more about the GRAIL mission in this MIT news story.


Zuber Group

The Gravity Recovery and Interior Laboratory, GRAIL

Twice the challenge? Getting the two spacecraft where they need to be, when they need to be there, requires an extremely challenging set of maneuvers never before carried out in solar system exploration missions - Image: NASA.

Zuber and her group. Maria with students at the GRAIL launch. From left to right: Michael Sori, Frank Centinello, Alexander Evans, Maria Zuber, ZhenLiang Tian, Matthieu Talpe, Anton Ermakov, Yodit Tewelde. Missing from photo: Peter James - Image: Dr. Sami Asmar, Jet Propulsion Laboratory and GRAIL Science Team member.

Meet Mike Sori | Interview with third year, Zuber Group, graduate student, Michael Sori - Video: Helen Hill.