In October 2008, a meteorite exploded above the Sudan, scattering fragments of diamond-encrusted rock across the Nubian Desert; pieces that scientists now believe came from a “lost planet” in the early solar system.
Analysis of the meteorite revealed compounds similar to those found on Earth diamonds, including chromite, phosphate and iron-nickel sulfides. This is the first time such compounds have been found in an extraterrestrial body, and it suggests the meteorite was formed under intense pressure – deep beneath a surface of a long-destroyed planet.
“We are doing archaeology, looking into the past, and trying to decipher the story of the solar system,” said Philippe Gillet, a senior author on the study, published by Nature Communications.
The researchers say the planet would have been between Mercury and Mars in size. It has long been thought the early solar system contained a number of “embryonic” planets, which would have been repeatedly broken and reformed over a period of 10 million years before the planets we know and love today came into being. Up to now, however, no remnants of these “lost” planets have never been identified.
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The meteorite is known as “Almahata Sitta”, which is Arabic for “Station Six” and the name of a train station close to where the rock scattered between Wadi Halfa and Khartoum. Telescopes tracked it as it approached Earth, where it exploded in the planet’s atmosphere above the Nubian Desert. A recovery effort by the University of Khartoum found 480 pieces of the mysterious material.
The first hint of the meteorite’s exotic origin came after it was discovered to be made of a rare stony compound called ureilite. Unlike other meteorites, this material isn’t tied to a known ‘parent body’, such as the moon or Mars. Further evidence came when the researchers examined the diamonds in the meteorite, and found they are much larger than those associated with collisions between other space rocks. Some measure 100 micrometres in length, which are large enough to suggest they may have been formed under intense pressures far beneath a planet’s surface.
A team of Swiss and Japanese researchers argued in 2015 that these relatively large diamonds were evidence of the meteorite’s planetary origin. Now, they’ve bolstered this theory with further evidence pointing to traces of an iron-sulphur compound that requires pressures of greater than 20 gigapascals to form.
“This level of internal pressure can only be explained if the planetary parent body was a Mercury- to Mars-sized planetary ’embryo,’ depending on the layer in which the diamonds were formed,” the researchers said in a statement.
As the first potential evidence of a “lost planet”, the fragments of rock could offer a crucial insight into the early days of our solar system, a tempestuous swirl of nascent planets. Given that there are still mysteries about our current solar system – including the potential existence of ‘Planet Nine’ – it could help us to better understand how our planetary neighbours formed.
Image credit: 2018 EPFL / Hillary Sanctuary
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