Gravitational anomaly found under the Moon’s far side

 2000 miles wide gravitational anomaly under the Moon’s far side (June 2019)

 

This false-color graphic shows the topography of the far side of the Moon. The warmer colors indicate high topography and the bluer colors indicate low topography. The South Pole-Aitken (SPA) basin is shown by the shades of blue. The dashed circle shows the location of the mass anomaly under the basin. [NASA/Goddard Space Flight Center/University of Arizona]

The GRAIL paired spacecrafts are tuned to detect gravitational anomalies, and were in operation most of 2012 to map the moon G field ; they allowed us to discover a 2000 miles wide gravitational anomaly under the Moon’s far side, precisely buried several miles deep beneath the South Pole-Aitken basin.

Baylor University’s researchers just published their findings after a thorough study of the GRAIL/NASA data – NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission – in the journal Geophysical Research Letters.

The two GRAIL spacecrafts are set to fly one in front of the other to detect very small density fluctuations in the Moon’s gravitational field. The leading spacecraft (called “Ebb”), when flying over a region of higher gravitational density, will slightly accelerate just a moment before the trailing spacecraft (“Flow”) will get to register that higher density (and thus gets accelerated in its turn). In between those two events, the distance between the two spacecrafts has been increased. Thus, by minutely measuring the distance between the two GRAIL spacecrafts, scientists are able to map precisely the gravitational field of the surface above which they fly.

Peter B. James, lead author of the Baylor University’s study, compared the “unexpected mass” they found burried underground the basin to “a pile of metal five times larger than the Big Island of Hawaii.”

Ian O’Neill, in his article on astroengine.com (ref. below) agrees with Peter James et al that this mysterious mass could bring us the key to the mystery of the moon formation 4 billion years ago. He ponders :

“How did all that material end up buried inside the Moon’s mantle? The South Pole-Aitken basin was created four billion years ago in the wake of a massive asteroid impact. In fact, the basin is known to be one of the biggest impact craters in the solar system. If this crater was formed by an impact, it stands to reason that the gravitational anomaly is being caused by the dense metallic remains of the massive asteroid that met its demise when the Earth-Moon system was in the throes of formation.” In other words, “it’s likely the massive metallic corpse of an ancient asteroid.”

Peter James et al write: “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.” Another explanation, according to the authors, is that this burried mass could be an accumulation of “dense oxides associated with the last stage of lunar magma ocean solidification.”

O’Neill concludes : “It just so happens that we currently have a mission at the basin, exploring this strange and unexplored place. On Jan. 3, the Chinese Chang’e 3 mission achieved the first soft touchdown on the lunar far side, landing inside Von Kármán crater and releasing a robotic rover, Yutu-2, to explore the landscape. At time of writing, the mission is ongoing.”

Let’s stay tuned on this exciting discovery and what it will unveil about our moon!

--------------------------------------------------------  Refs --------------------------------------------------------------

·         There’s Something Massive Buried Under the Moon’s Far Side, by Ian O'Neill at https://astroengine.com/2019/06/11/theres-something-massive-buried-under-the-moons-far-side/

·         Peter B. James, et al. Deep Structure of the Lunar South Pole‐Aitken Basin. Geophysical Research Letter. First published: 05 April 2019. https://doi.org/10.1029/2019GL082252

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First image of a black hole and its event horizon in Messier 87 (April 10 2019)

 Breakthrough: FIRST IMAGE OF A BLACK HOLE AND ITS EVENT HORIZON (in Messier87, April 10 2019)

As scientists know, most “active” galaxies house “supermassive black holes” right in their centers, and thought to be their gravitational engines; but up to now black holes had only been detected indirectly, sometimes by the curving of the light of a galaxy (reaching us) when a black hole passes in front of it -- and creating an apparent ring or gravitational lensing --, or by the jets they emit, mostly gamma rays.

On April 10, 2019, was published the first image of a supermassive black hole surrounded by its event horizon, the one set at the center of Messier 87, a large elliptical galaxy in the constellation of Virgo (part of our neighboring Virgo Galaxy Cluster). The ring shape on this image is “the bright emissions from the hot gasses immediately surrounding the colossal maw of a supermassive black hole’s event horizon” explains the Perimeter article.*  

This supermassive black hole has a mass of 6.5 billion Suns, is ½ light-day across, and is 55-million light-years away. To give an idea of its gigantism, our own supermassive black hole in the center of our galaxy the Milky Way -- called Sagittarius A*, or Sgr A* for short – is 2.6 million solar masses, thus about 2500 times less massive.

(see image: Sagittarius A*, image taken with NASA's Chandra X-Ray Observatory. Ellipses indicate light echoes. Full-field is 12.5 arcmin across.)

It took almost two decades to create the EHT - the Event Horizon Telescope -  a network of radio telescopes around the world that creates an Earth-sized virtual telescope; EHT uses Interferometry to combine images taken from widely distant observatories distributed all over earth, to gain a higher resolution picture.

Avery Broderick (professor at the University of Waterloo, associate faculty member at Perimeter Institute for Theoretical Physics, Cambridge, UK), is one of the key scientists and theorists of the project. The University of Waterloo’s News release, said about these black holes, referring to him,  “This first image is undeniable proof of their existence and is a robust test of general relativity in the most extreme gravitational environment known, added Broderick. ‘A black hole is a gravitational feature that comes right out of Einstein’s theory of general relativity, first described over a century ago and implicated – but never proven – to exist. Until now.’” (https://uwaterloo.ca/news/news/first-image-black-hole-captured) Broderick disclosed that their next target was to be our own supermassive black hole, Sgr A*,  as well as tracking the dynamics of these two.

“We now have exceptionally strong evidence for the link between supermassive black holes and the centres of active galaxies – this is how black holes shape our universe on galactic scales,” said EHT project director Sheperd S. Doeleman.

* See https://insidetheperimeter.ca/black-hole-breakthrough-astronomers-release-landmark-image/

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