The Procellarum volcanic soil region is a roughly circular, about 1,800 miles in diameter, almost as wide as the United States. One hypothesis that was formed by a massive impact, in which case it would have been the largest impact basin on the Moon. Subsequent collisions of asteroids sobreimpresionaron the region with smaller basins remained large ones though.
Now, researchers at MIT (Massachusetts Institute of Technology, Boston, USA), Colorado School of Mines, and other institutions, have created a high-resolution map of the Procellarum, and found that its edge is not circular but polygonal, consisting of sharp angles that could not have been created by a massive asteroid. Instead, the researchers believe that the angular outline was produced by giant cracks in the crust of the Moon produced on cooling the ground around a plume of hot material that emerged from deep inside the satellite.
Maria Zuber, a professor of geophysics and vice president of research at MIT, says the MIT News information that as cracks occurred, formed a “plumbing system” in the crust of the Moon whereby the magma may meander toward the surface.
The magma eventually filling the smaller basins in the region, creating what we see today as dark spots on the visible side of the Moon, characteristics that inspired the idea of ”man in the moon. ” Zuber and his colleagues report their findings this week in the journal Nature .
calculations
The team mapped the Procellarum region using data from -sondas Grail twins who orbited the moon in December 2012-January. The researchers measured the distance between the probes as they chased each other around the Moon.
When a probe passed over a region of lower density, slowed briefly captured by the gravitational attraction of the region. Probes thus moved accordion toward or away as the surface density.
Using the variable distance between the probes, Zuber and his team determined the force of gravity on the surface of the moon, creating a very detailed map, used to determine where the lunar crust thickens and thins.
From this mapping, the researchers found that the edge of the Procellarum region was composed of abutted edges at angles of 120 degrees. Since asteroid impacts tend to produce circular or elliptical craters, Zuber says the angular form of Procellarum could not have been caused by an impact.
Instead, the team explored an alternative scenario: Some time after the Moon was formed formed and cooled, a large plume of molten material rose from the interior of the Moon, near where today Procellarum region. The pronounced difference in temperature between the plume of magma and crust around it caused the surface to shrink over time, creating a pattern of fractures that served as a conduit for the molten material reached the surface.
To test the hypothesis, the researchers modeled the gravitational signal of the region in the event that any volcanic intrusions: magma seeping up just below the surface of the Moon and, eventually, cooled and crystallized . The resulting simulation matches the gravity signal recorded by Grail, supporting the idea that Procellarum was caused by a plume of magma, and not an asteroid.
“How such a plume rose remains a mystery,” says Zuber. “It could be due to the radioactive decay of elements that produce heat deep inside. Or possibly a big impact early caused the plume. But in the latter case, all evidence of such an impact have been completely erased. The people who thought everything volcanism was associated with a large impact should think a little more about it. ”
Ultimately, demonstrating that the moon could have housed an old plume may require a new lunar mission, involving a long-term geophysical network that tracks the seismic signals and heat from the deep interior, according to Clive Neal, a professor at the University of Notre Dame (Indiana, USA).
“It’s about trying to understand the nature of the interior, and how extensive was this concentration of heat producing elements which would have caused a column ascended to the surface,” says Neal, who was not involved research. “Grail has been a fantastic mission, and these data will be continually used and reinterpreted as we get more data from the Moon.”
Jeffrey C. Andrews-Hanna, Jonathan Besserer, James W. Head III, Carly JA Howett, Walter S. Kiefer, Paul J. Lucey, Patrick J. McGovern, H. Jay Melosh, Gregory A. Neumann, Roger J . Phillips, Paul M. Schenk, David E. Smith, Sean C. Solomon, Maria T. Zuber: Structure and evolution of the Lunar Procellarum region as revealed by GRAIL gravity data. Nature (2014). DOI: 10.1038 / nature13697
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