An article published in the journal “Nature Communications” describes a study of microscopic diamonds discovered inside the Almahata Sitta meteorite, a fragment of a larger meteorite exploded in the Earth’s atmosphere on October 7, 2008. A team of researchers analyzed those diamonds concluding that they contain compounds that can only form within a planet, so they must be the remnants of a lost planet with a size between that of Mercury and Mars.
On October 7, 2008, the meteorite cataloged as 2008 TC3, with a mass estimated at about 80 metric-tons and a diameter of just over 4 meters, exploded in the Earth’s atmosphere at a height of about 37 kilometers (about 23 miles) above the Nubian desert, in Sudan. I was spotted the day before by Richard Kowalski of the Catalina Sky Survey, who consequently was able to provide the information necessary to observe it and predict its impact’s timeline.
Many fragments were recovered even if their total mass is just over 10 kg (about 23 lbs) and analyzed by various institutions including NASA. This allowed to quickly understand that its nature was unusual given that it was an ureilite, with a composition quite different from that of other rocky meteorites. One of its characteristics is a percentage of carbon around 3%, much higher than normal, which can be in the form of graphite but also of microscopic diamonds.
The crystallization of carbon that generates diamonds is due to very high temperature and pressure conditions. In the case of the nanodiamonds present in the ureilites in general the explanation is in shock waves caused by violent collisions of the ureilite with other asteroids. However, they’re called nanodiamonds exactly because their size is a few millionths of a millimeter while the ones found in the Almahata Sitta meteorite reach 100 micrometers in length, many thousands of times greater than normal.
Already in 2015 a first analysis of those microscopic diamonds made a team of researchers suspect that their origins could be in a lost planet but they needed evidence. After more time and other analyzes, the researchers found that the diamonds in the Almahata Sitta meteorite contain fragments of an iron-sulfur compound that gets formed only at pressures above 20 GigaPascals. The conclusion is that they must have formed within a planet with a size between that of Mercury and Mars.
The top high-angle annular dark-field (HAADF) electron microscope image (Nature Communications / Farhang Nabiei et. al.) shows diamond segments with a similar crystallographic orientation. The dashed yellow lines show the boundaries between diamonds and graphite. The right image corresponds to the green square on the left image. The orange line shows the iron-sulfur compound’s inclusion trails.
If the conclusions of the researchers are correct, they still have to understand where’s the planet from which the Almahata Sitta meteorite originated. According to the solar system’s formation models, originally there were several planetoids and perhaps small planets that were later destroyed in collisions or absorbed by other planets. A small planet may have hit the primordial Earth, causing the formation of the Moon.
Philippe Gillet, a planetary scientist at the Federal Institute of Lausanne, Switzerland, one of the authors of the study, stated that the Almahata Sitta meteorite could be one of the remnants of the first generation of planets in the solar system. Gillet has already been involved in meteorite studies and simulations of ancient impacts in the past.
According to Farhang Nabiei, the first author of the article and also of the Federal Institute of Lausanne, all the ureilites come from the same planet or protoplanet, which may have lasted only a few million years. For this reason, he intends to search and analyze other similar meteorites to look for other clues to their origins.