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Diamonds of a Lost Planet

May 21, 2018

People like a good mystery, and that's why there have been so many detective shows on television. A moment's reflection tells us that TV detectives act like scientists, collecting and analyzing evidence and proposing theories to explain the facts. The shows are written such that the final exposure of the culprit of a crime often hinges on a seemingly obscure observation.

In the television series, Columbo, the detective played by Peter Falk has many personal attributes typically ascribed to the stereotypical absent-minded scientist, all of which belie his problem-solving skills. In one episode, the crucial piece of evidence was the fact that the quantity of cigarette ash in an ashtray was not representative of what was smoked. That's some fine detective work, Chief!

Sherlock Holmes examining evidence

"Watson, what's this? A four-leaf clover! Do you know what that means?

"That there's another clover there with just two leaves?"

Sherlock Holmes, the fictional private investigator of Arthur Conan Doyle, is the world's most famous detective. Holmes supposedly wrote a monograph on tobacco ashes, the likely inspiration for the Colombo episode mentioned above.

Basil Rathbone played Holmes in a series of films made between 1939 and 1946, with Nigel Bruce as Dr. Watson. Bruce played Watson as a confused and bumbling foil to Holmes.

(Illustration by Sidney Paget(1860-1908), via Wikimedia Commons


To increase their popularity, many television science shows are now written like detective shows. A "scientific mystery" is presented, evidence is collected and analyzed, scientists discuss theories that support the evidence, and a scientific consensus is stated. This detective-themed presentation captures viewer interest, which is also enhanced by scientific visualizations. These visualizations are a startling advance from the science films of my elementary school days, as parodied in many episodes of The Simpsons.[1-2]

Scientists, as well as detectives, are not just interested in the presence of something, but also its absence. In Doyle's 1862 The Adventure of Silver Blaze, Holmes was interested in "... the curious incident of the dog in the night-time," which was a non-barking dog. The absence of a bark indicated that the dog was familiar with the culprit. In astronomy, the problem of the "missing mass" of the universe has stimulated research since the 1970 paper by Vera Rubin (1928-2016) and Kent Ford (b. 1931) on the discrepancy between observed and theoretical galactic rotation rates.[3]

While the planets of our Solar System seem to orbit in regular, immutable paths, a concept known as the clockwork universe, this is merely an illusion that arises from limited observations. The Earth-Moon system was created by a collision of an early Mars-sized planet, Theia, with a proto-Earth object commonly called Gaia about 4.5 billion years ago.

Image of the fill Moon (Galileo spacecraft, December 7, 1992)

Earth's Moon, as imaged by NASA's Galileo spacecraft on December 7, 1992.

The Earth is the only planet in our Solar System to have a huge, solitary moon. As I discussed in some previous articles (Lunar Origin, November 28, 2016, and Synchronizing to the Moon, April 11, 2016), the presence of the Moon may have been important to the genesis and evolution of life on Earth.

(NASA image, via Wikimedia Commons)


Theia was just one of many protoplanets in the early Solar System whose fate was to either coalesce into a larger planet, or blasted apart into asteroids. Some of these protoplanets would have been as large as Mercury, and they may have existed for a considerable period, replicating many geological processes that exist on Earth. One such geological process would have been the formation of diamond under the high pressures existing at the protoplanetary cores.

A team of scientists from the École Polytechnique Fédérale de Lausanne (Lausanne, Switzerland), the Sorbonne Paris Cité (Paris, France), the Universität Bayreuth (Bayreuth, Germany), and the Université de Bretagne Occidentale (Plouzané, France) have now published evidence of the existence of at least one such protoplanet in the analysis of diamonds found in fragments from the 2008 in-fall of a large meteor in Sudan.[4-10] Their analysis is published as an open access article in Nature Communications.[4]

It's conjectured that tens of such protoplanets between the size of the Moon and Mars formed the terrestrial planets of today's Solar System by crashing into each other and coalescing into our present planets.[4,8] This process would have happened in the first ten million years of the existence of the Solar System.[8] A 2015 examination of the diamonds found in the fragments of the 2008 Sudan meteor indicated that they were too large to have been created by impact forces between asteroids, so they might have been created in the core of one of these lost protoplanets.[10] The present study adds credence to this conjecture.

The asteroid that deposited fragments in Sudan in 2008 is now known as 2008 TC3. It entered Earth's atmosphere on October 7, 2008, and exploded 37 kilometers above the Nubian Desert.[4] This asteroid was slightly larger than four meters in diameter, weighed about 80 metric tons, and it exploded into many fragments across the desert.[5,8] These fragments, 47 of which ranged in size from 1-10 centimeter and a total mass of 4.5 kilograms, were recovered as the Almahata Sitta meteorite.[5,8] What was unique about this meteorite is that its asteroid was tracked from discovery all the way to landfall using telescopes, the first time that an asteroid impact was predicted.[6,8]

Fragment of meteorite 2008-TC3, Almahata Sitta

Fragment of the Almahata Sitta meteorite.

This meteorite originated from the 80 metric ton asteroid 2008 TC3, which was 4.1 meters in diameter.

About 600 fragments of this meteorite with a total weight of 10.5 kilograms have been found in the Nubian Desert of Sudan.

(NASA image, via Wikimedia Commons)


The Almahata Sitta meteorite is a rare type known as an ureilite, a class of carbon-rich stony meteorites that often contain clusters of nanoscale diamonds and don't originate from the Moon or Mars.[5,8-9,10] The contained diamonds are up to 100 micrometers in size, which is at least 100 times larger than nanodiamonds that form by impact, thus the conjecture that they were produced in a protoplanetary core.[6]

The ureilite fragments consist of the minerals, olivine and pyroxene.[4] The research team found that the nanodiamonds were in clusters having almost identical crystallographic orientation, and they contained inclusions of chromite, phosphate, and (Fe,Ni)-sulfide, two things that could only happen if they were formed over an extended period under a pressure higher than 20 GPa, as inside a protoplanetary core.[4-5]

The analysis was done using transmission electron microscopy, electron energy-loss spectroscopy, and energy dispersive X-ray analysis.[4] The crystallographic orientation of the diamonds was by electron diffraction, and their morphology was studied using transmission electron microscopy.[4] Farhang Nabiei, a study author from the École Polytechnique Fédérale de Lausanne, is quoted in the National Geographic as saying, "Normally we talk about telescopes [to study space]. Here we are talking about the past, so it's different. Here we use the electron microscope... It is the first time that we found inclusions in extraterrestrial diamonds."[7]

Inclusions in Almahata Sitta meteorite nanodiamonds

Inclusions in Almahata Sitta meteorite nanoscale diamonds. The left shows an electron micrograph, and the right is an energy dispersive X-ray element map showing iron in blue and sulfur in red. Color choice in such element maps is arbitrary, but I would have selected red for iron and yellow for sulfur. (Portion of fig. 3 of ref. 4, published under the Creative Commons Attribution 4.0 International License.)[4]


While the nanoscale diamonds could have formed at the core of a protoplanet of the size of Mercury or larger, they might also have formed just outside the core of another of Mars-size protoplanet or larger.[6] There are 480 ureilite meteorites, so there's potential for other insights into the protoplanets and early evolution of the Solar System.[7,9]

References:

  1. The Simpsons - A World Without Zinc, YouTube Video by jasefest, October 5, 2011.
  2. Lisa's class watches movies "Sand" and "The Moon of Earth" from The Simpsons: S8 E25 - "The Secret War of Lisa Simpson," YouTube Video by mrant27, June 13, 2013.
  3. Vera C. Rubin and W. Kent Ford, Jr., "Rotation of the Andromeda Nebula from a Spectroscopic Survey of Emission Regions," Astrophysical Journal, vol. 159 (February, 1970), pp. 379ff., DOI: 10.1086/150317.
  4. Farhang Nabiei, James Badro, Teresa Dennenwaldt, Emad Oveisi, Marco Cantoni, Cécile Hébert, Ahmed El Goresy, Jean-Alix Barrat & Philippe Gillet, "A large planetary body inferred from diamond inclusions in a ureilite meteorite," Nature Communications, vol. 9, Article no. 1327 (April 17, 2018), doi:10.1038/s41467-018-03808-6. This is an open access article with a PDF file here.
  5. Meteorite diamonds tell of a lost planet, Ecole Polytechnique Fédérale de Lausanne Press Release, April 17, 2018.
  6. Sid Perkins, "Diamond-studded meteorites came from the collision of a lost planet," Science, April 17, 2018, doi:10.1126/science.aat9001.
  7. Sarah Gibbens, "Diamonds From Outer Space Formed Inside a Long-Lost Planet," National Geographic, April 17, 2018.
  8. Henry Bodkin, "Sudan diamonds evidence of early planet roaming the solar system," Telegraph (UK), April 17, 2018.
  9. Charles Choi, "Meteoric Diamonds Are Evidence of Long Lost Planets," Astronomy, April 17, 2018.
  10. Ian Sample, "Diamonds in Sudan meteorite 'are remnants of lost planet'," The Guardian (UK), April 17, 2018.

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