An artist’s depiction of the washing machine-sized twin spacecraft (Ebb and Flow) that make up NASA’s Gravity Recovery And Interior Laboratory (GRAIL) mission, headed by Maria Zuber, a geoscientist at MIT.
The moon’s battered crust is riddled with deep fractures that may extend miles underground, according to the first findings from two NASA spacecraft orbiting Earth’s nearest neighbor.
The results of the mission, led by a Massachusetts Institute of Technology scientist, surprised researchers, who said it will provide new insight into the evolution of the early solar system, and even help inform the search for life on Mars.
Announced Wednesday, the discoveries are also a reminder that the familiar moon still holds secrets four decades after NASA ended its manned missions there.
“We have known that the moon’s crust and other planetary crusts have been bombarded by impacts, but none of us could have predicted just how cracked the lunar crust is,” said Maria Zuber, the MIT geoscientist who led the mission, called GRAIL.
The findings were announced at the meeting of the American Geophysical Union in San Francsico, and published online by the journal Science Express.
Two washing machine-sized spacecraft, called Ebb and Flow are circling the moon, now swooping within about four miles of its cratered landscape. They measure tiny fluctuations in its gravity, giving scientists a precise picture of the interior by keeping close track of their position relative to one another. If one of the spacecraft flies over an area with dense rock, for example, the gravity will change the distance between the two spacecraft.
The moon’s pulverized surface and interior are akin to a history book written in the language of geology—formations of craters, underground rock formations, fractures, and dikes. Decoding these through a highly detailed gravity map can provide information about what the rocky planets were going through right at the time life was arising on Earth. That record is no longer visible on Earth because of plate tectonics—the slow-motion shifting and collisions of slabs of rock. Understanding the moon, and how it formed, is more than a matter of history, however: the deep fractures found on the moon, Zuber thinks, might suggest one way early life could have taken refuge on other planets, if it existed.
“There isn’t a lot of water in the moon, but think about Mars,” said Zuber, who is the first woman to head a NASA planetary mission. “The Martian crust must be similarly fractured up, and Mars used to have an ocean on its surface. ... If there ever was life on Mars, and the climate on Mars changed drastically and early microbes need to find a place to live, they could’ve made their way into the deep surface and gone deep into the crust, where it would have been warmer and more hospitable.”
Zuber said that her team will continue to analyze the data from the mission for years, and that at some point when the mission is over, the spacecraft will crash onto the moon.
In three separate papers, the scientists, also reported that the moon’s crust is thinner than had previously been thought, and that bombardment by asteroids and comets had likely exposed parts of the moon’s interior near craters. To Zuber, that’s exciting, because it means scientists could analyze the makeup of rocks on the surface to get information about the interior, which could help explain how the moon and Earth system evolved.
The dominant explanation for how the moon evolved is the “giant impact theory,” which says that a Mars-sized projectile slammed into the early Earth, and the moon coalesced from the debris ejected from the collision. Data collected by Ebb and Flow allowed scientists to estimate the amount of aluminum in the moon’s crust, showing that it is the same as on the Earth—support for the giant impact theory. To make that calculation, scientists used the gravity measurements, which told them the density of the crust, along with data taken by other instruments that analyzed the composition of the crust.
Robin Canup, associate vice president of the Southwest Research Institute in Boulder, Colorado, who was not involved in the research, said she was particularly fascinated by one of the papers, which found evidence there was an early period when the moon was getting bigger. Understanding the early conditions of the moon, including how hot its core was, could help scientists understand how it formed, Canup wrote in an e-mail.
“Some of the lunar origin scenarios produce a fully molten Moon, while others may produce a cooler initial lunar interior that may be more consistent with prior thermal models and the new results,” Canup wrote.
The mission provides important new information for scientists, but is also a major accomplishment for Zuber, who has spent the past five years working on, and at times worrying about, the many aspects of the mission. She is the first woman to lead a major planetary NASA mission, an accomplishment that she is quick to deflect.
“For me, the most gratifying thing is just that it worked,” Zuber said. “We have the privilege of exploring space. .... To me this is a very sacred thing that we have the privilege of public support for science in this country, so I take that very seriously.”