Top Story: December 10, 2012

Latest from GRAIL


NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission was launched in the fall of 2011, and began its scientific mission around the Moon in March of this year. GRAIL includes two washing machine-sized probes that measure the gravity of the lunar surface. The spacecraft, named Ebb and Flow by elementary students in Montana, orbit the Moon at a very low altitude, about 34 miles, gathering such precise data that scientists are not only confirming theories about the Moon's formation, but also learning surprising new things about its geological history.

Mapping gravity not only teaches scientists about the surface of a planet or moon, but also reveals information about the crust, internal structure, and composition. The gravity map the GRAIL mission has created of the Moon "is the best of any planet, including Earth," according to Maria Zuber, principal investigator for the mission. It reveals an abundance of features never before seen in detail, such as tectonic structures, volcanic landforms, basin rings, crater central peaks and numerous simple, bowl-shaped craters. Data also show the Moon's gravity field is unlike that of any terrestrial planet in our solar system.

These are the first scientific results from the prime phase of the mission, and they are published in three papers in the current issue of Science. They were also presented at last week's AGU meeting.

At the meeting, co-investigator Mark Wieczorek spoke about the crustal density of the Moon. Data from GRAIL find the average crustal thickness between 21 and 27 miles, quite a bit thinner than previously thought.  "With this crustal thickness, the bulk composition of the Moon is similar to that of Earth. This supports models where the Moon is derived from Earth materials that were ejected during a giant impact event early in solar system history."

The theory of the giant impact event purports that the Moon was created from debris after a large collision between Earth and another planetary body. In this case, then, the Moon should have very similar materials to Earth, just as Wieczorek found.

Another scientist, Jeff Andrews-Hanna, discovered new volcanic properties on the Moon, unseen in other missions. He found ancient dikes and believes that these structures likely formed in the first billion years of the Moon's history. As the debris following the giant impact formed to become the Moon, it probably warmed up and expanded, creating these magmatic structures. There are theories of this early warming on the Moon, and this could be the first physical evidence.

When GRAIL's first mission ended on May 29, there was enough fuel left to continue the gravity science. The second science mission will conclude on December 17. As the end of that mission nears, the spacecraft will operate at lower orbital altitudes above the Moon, providing very different data from what was collected in the spring.

Ebb and Flow are also providing other information to much younger scientists. A series of cameras on the spacecraft, called MoonKAM, is taking pictures as it flies over locations on the Moon. The cameras are directed by youth in schools all over the world as a part of the Sally Ride Science Institute in San Diego--the students provide NASA with targets of what they want to see. Sami Asmara, of NASA/JPL, explained the reason for this. "We want to get the next generation excited about lunar science." Maybe we'll see the result of these endeavors at an AGU meeting in the future?

Do you want to see images and models from the GRAIL mission? Follow this link.


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