Scientists have long known that the moon and other rocky bodies in the inner solar system were pounded by impacts early in their history billions of years ago, but new evidence shows that the intensity of the impacts was greater that previously thought.
Space.com reports that NASA's twin Gravity Recovery and Interior Laboratory (GRAIL) probes have created an accurate gravity map of the moon which shows that the moon's crust was subjected to intensively pulverizing impact early in its history.
The evidence from GRAIL suggests that the Earth, Mercury, Venus and Mars must have endured similar massive pounding more intense that ever suspected billions of years ago. The evidence pointing to the intense repeated bombardment of the lunar surface by asteroids and comets in their early comes as a surprise to scientists.
Space.com reports that GRAIL principal investigator Maria Zuber of MIT, during a press conference at the annual fall meeting of the American Geophysical Union, said the discovery "really opens a window to this early stage of just what a violent place the surfaces of all terrestrial planets were early in their history."
NASA reports Zuber said "It was known that planets were battered by impacts, but nobody had envisioned that the (Moon's) crust was so beaten up. This is a really big surprise, and is going to cause a lot of people to think about what this means for planetary evolution."
The new measurements were used to create a new lunar gravity map described as the highest resolution map ever obtained for any body.
The new data reveals that the lunar crust is extremely porous, suggesting the moon was literally pulverized by repeated and intensive impacts. Scientists estimate that around 98 percent of the crust is deeply fragmented, porous material caused by early massive impacts.
According to NASA, the moon’s highly fragmented surface preserves the evidence of its past history because unlike the Earth, the moon's crust is not geologically active, that it, it does not exhibit plate tectonics which involves movement of massive slabs of the rocky crust that reshapes and remolds the structure of the crust continually.
According to NASA, GRAIL scientist Mark Wieczorek, said the probes also found that the crust of the moon is thinner than previously thought—about 21 to 27 miles (34 to 43 kilometers), compared to earlier estimates of 30 to 40 miles (48 to 64 km).
"This image depicting the porosity of the lunar highland crust was derived using bulk density data from NASA's GRAIL mission and independent grain density measurements from NASA's Apollo moon mission samples as well as orbital remote-sensing data.
Ebb and Flow also discovered several extensive subsurface "dikes" that run up to 300 miles (480 km). The "dikes" provide scientists with evidence in support of the Giant Impact hypothesis of the moon's formation. According to the scientists the subsurface dikes can only be explained if it is assumed that the moon's crust was expanding early in its history as the moon's interior heated up and expanded.
According to the Giant impact hypothesis, a body about the size of Mars collided with the Earth about 4.5 billion years ago. The moon was formed from a piece or pieces of the Earth broken off and blasted into space at the impact. The Daily Mail reports a paper published last year that suggested the Earth once had two lunar satellites that coalesced to form the moon we see today. But Zuber said high-resolution mapping by the spacecraft did not find evidence for the controversial hypothesis.
NASA reports that GRAIL guest scientist Jeff Andrews-Hanna of the Colorado School of Mines, said: "The process of building a moon out of that debris should result in a situation where the moon is cooler on the inside and warmer on the outside. And then what naturally happens is that the interior will warm up and expand during that first billion years."
He added: "This had been predicted theoretically a long time ago, but there was no direct observational evidence to support this period of early lunar expansion until this GRAIL data."
Life on MarsNASA's GRAIL data not only provides new insight into how the moon was formed, it also yields new clues about where on Mars life may be found, if ever there was life on the planet.
Now scientists know that the uppers crusts of the terrestrial or rocky planets in the inner core of the solar system must be very highly and deeply fractured. These cracks could provide channels for liquid matter on the surface of a rocky planet. Scientists now postulate that the ocean that many experts believe existed on the surface of Mars earlier in its history may have sunk underground through the fissures created by impacts.
Zuber puts the hypothesis simply: "That ocean could well be underground."
The implication is that if we are looking for evidence of life on Mars, we may have to look underground. Space.com reports Zuber said that microbes "could have gone very deep within the crust of Mars."
According to NASA, the twin probes, named Ebb and Flow, were launched in September 2011 to map the moon's gravity field with higher standard of precision than previously achieved. As the twin spacecraft fly in a formation around the moon, their sensors detect very small changes in the distance between them caused by the undulating terrain of lunar mountains, craters and other subsurface formations.
The data now available pertains to the primary mission of the twin probes that ended in May. The two probes are now on an extended mission that will end in mid-December after which they will be crashed onto the lunar surface.