Scientists can't explain mysterious large mass discovered on Moon

James Marshall
June 11, 2019

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.

James and his colleagues discovered the blob while comparing maps of lunar topography with data collected by NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission - a 2011 experiment wherein two satellites orbited the moon in tandem, mapping the precise strength of its gravitational pull at various locations.

"Imagine taking a pile of metal five times larger than the Big Island of Hawaii and burying it underground", Peter B. James, a geoscientist at Baylor University, said in a press release.

The South Pole-Aitken basin on the far side of the moon is said to be the largest crater in the solar system and extends several miles deep.

'One of the explanations of this extra mass is that the metal from the asteroid that formed this crater is still embedded in the moon's mantle'.

The research is described in a paper published April 5 in the journal Geophysical Research Letters.

This false-color graphic shows the topography of the far side of the Moon.

The dense mass - "whatever it is, wherever it came from" - is weighing the basin floor downward by more than half a mile, he said. This, according to researchers, is an anomaly that exists on the surface because of metallic remnants dislodged from the core of the massive impact that formed the South Pole-Aitken (SPA) basin.

The researchers' simulations imply the material could be an asteroid's iron-nickel core, which, if dispersed into the upper mantle, could be weighing down the basin.

Another possibility is that the large mass might be a concentration of dense oxides associated with the last stage of lunar magma ocean solidification. This magma ocean, which is thought to have existed 70 million years after the solar system was formed, gradually crystallized to the solid, grainy rock that resembles the Moon today over the next 200 million years.

An impact basin is an impact crater with a rim diameter of more than 186 miles and there are 40 such impact basins on the moon, explains Lunar Science and Exploration.

For these reasons, geologists are eager to explore the basin to glean clues about the moon's formation and composition.

When it comes to the South Pole-Aitken basin, the topography is particularly striking. When the scientists combined the two types of data, they saw a mismatch between the surface topography and the gravitational tug of the moon.

In addition to the number of "cold traps" of ice-water confirmed by the Chandrayaan-1 mission and studied by robotic probes in the Moon's South Pole, there are also regions that have a magnetized crust.

"Stratigraphic relationships show that SPA is the oldest impact basin on the moon, but scientists are intensely interested in just how old it is".

Whatever formed the basin almost 4 billion years ago remains a mystery, but the blow was so strong that it likely punched all the way through the moon's crust and tossed part of the lunar mantle - a deeper geologic layer - onto the surface.

Other reports by Click Lancashire

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