Astronomers Detect a Huge, Unexplained Mass
Under a Giant Crater on The Moon
11 JUN 2019
" The Moon is home to one of the largest known impact craters in the Solar System. At 2,500 kilometres (1,550 miles) across, the South Pole-Aitken Basin on the Moon's far side covers nearly a quarter of the lunar surface - and there's something massive buried beneath it.
We can't see it from here on Earth, but detailed readings made using lunar orbiters indicate there is something huge enough under that crater to be causing a significant gravitational anomaly.
"Imagine taking a pile of metal five times larger than the Big Island of Hawaii and burying it underground," said geophysicist Peter James of Baylor University.
"That's roughly how much unexpected mass we detected."
The anomaly was discovered in two sets of data. The first was from NASA's GRAIL mission, a pair of orbiting spacecraft that mapped the Moon's gravitational field in 2011 and 2012 to try to shed some light on its interior structure.
This data had already indicated a gravitational anomaly, and that the basin had higher-than-average density compared to the rest of the lunar surface; the team attributed this to its iron-rich surface composition.
But when the team compared these findings with the lunar topography data collected by NASA's Lunar Reconnaissance Orbiter, the results showed something else: a mass of about 2.18 quintillion kilograms (that's a number with 18 zeroes), extending more than 300 kilometres (184 miles) below the surface.
This mass, the researchers believe, is weighing the floor of the basin downward by more than 800 metres, around 10 percent of its total depth, explaining a depression in the bottom of the basin previously attributed to contraction.
"One of the explanations of this extra mass," James said, "is that the metal from the asteroid that formed this crater is still embedded in the Moon's mantle."
According to computer simulations, if conditions are just right, the iron-nickel core of an impacting asteroid can be dispersed into the upper mantle, between the Moon's crust and core. "
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Edited by Atossa, 11 June 2019 - 05:55 PM.