According to a new study led by Prof Maria Zuber of MIT, Oceanus Procellarum – a vast mare on the western edge of the Moon’s near side – likely arose from a large plume of magma deep within the Moon’s interior, not from a massive asteroid impact as previously thought.
Top: the full Moon as seen from the Earth, with the Procellarum border structures superimposed in red. Image credit: Kopernik Observatory / NASA / Colorado School of Mines / MIT / JPL / Goddard Space Flight Center. Bottom: global maps of lunar properties – topography and gravity gradient. Image credit: Jeffrey C. Andrews-Hanna et al.
Oceanus Procellarum (Latin for ‘Ocean of Storms’) – a roughly circular, volcanic terrain some 3,200 km in diameter – has long been a source of mystery for scientists.
Some have suggested that the region is part of a giant basin formed by a massive asteroid strike early in the lunar history.
But the new study challenges the impact hypothesis.
Prof Zuber and her colleagues using data from NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission have produced a new high-resolution map of Oceanus Procellarum, and identified a series of linear gravitational anomalies forming a large rectangle, nearly 2,575 km across, running beneath the region.
“As asteroid impacts tend to produce circular or elliptical craters, the Procellarum’s angular shape could not have been caused by an impact,” said Prof Zuber, who is the senior author of a paper published in the journal Nature.
The scientists believe that this shape was produced by giant tension cracks in the Moon’s crust as it cooled around an upwelling plume of hot material from the deep interior.
“As cracks occurred, they formed a ‘plumbing system’ in the Moon’s crust through which magma could meander to the surface,” Prof Zuber explained.
“Magma eventually filled the Oceanus Procellarum‘s smaller basins, creating what we see today as dark spots – features that have inspired the popular notion of a man in the Moon.”
To test their hypothesis, the scientists modeled the Procellarum’s gravitational signal if it were to contain volcanic intrusions – magma that seeped up to just beneath the moon’s surface and, over time, cooled and crystallized.
The resulting simulation matched the gravity signal recorded by NASA’s GRAIL, supporting the idea that the region was caused by a magma plume, and not an asteroid.
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Jeffrey C. Andrews-Hanna et al. 2014. Structure and evolution of the lunar Procellarum region as revealed by GRAIL gravity data. Nature 514, 68–71; doi: 10.1038/nature13697
