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In Our Skies: Diamonds falling from the sky, Almahata Sitta

Alan Hale
Guest Columnist
Alan Hale

Last week’s edition of this feature discussed the very close flyby of Earth by the asteroid Apophis that will be taking place eleven years from now. We know about Apophis, and many other Earth-approaching asteroids, primarily as a result of comprehensive search programs for such objects that have been operating for the past two decades.

While the 2029 approach by Apophis is the closest by any somewhat-large asteroid that has happened or that will be happening during the intermediate-term future, there have been even closer approaches by very small asteroids.

Indeed, over the past few years there have been at least two incidences where a tiny asteroid was discovered while approaching Earth that later actually impacted our planet – although these particular objects were so small that impacted means that they disintegrated within the atmosphere.

The first and most celebrated such instance took place a little less than 10 years ago. The asteroid in question, a 13-foot-wide chunk of rock designated 2008 TC3, was discovered on Oct. 6, 2008, by astronomer Richard Kowalski with the Catalina Sky Survey program based near Tucson, Arizona. Calculations soon showed that Kowalski’s asteroid was headed directly towards Earth, and indeed, a little over 19 hours later it entered the atmosphere above northern Sudan.

The entire exercise provided a useful test of the procedures that have been put in place for a larger object that might be discovered on its way to an impact with Earth.

It exploded some 23 miles above the surface of a remote section of the Nubian Desert at a few minutes before 6 a.m. local time, and although this is a largely unpopulated area of Earth’s surface, the reports and images that were obtained indicated it was a spectacular sight.

While the asteroid itself exploded well above Earth’s surface, it nevertheless rained small meteorites onto the ground. Some 600 individual fragments, collectively weighing about 23 pounds, have now been recovered, and collectively they are referred to as the Almahata Sitta meteorite. One of the teams that located the fragments made sure to give one of them to Kowalski, thus far the only person on Earth who can claim to own a piece of “his own asteroid.”

The Almahata Sitta meteorite has turned out to be a member of a rather rare class of meteorites known as ureilites. Such meteorites are relatively rich in carbon and in carbon-containing substances; indeed, traces of as many as 19 different amino acids – which are sometimes considered as the building blocks of life – have been identified in Almahata Sitta. Nanodiamonds – small diamonds that are about the size of the thickness of a human hair – have also been found within Almahata Sitta.

A recent investigation of these nanodiamonds conducted by a team of scientists led by Farhang Nabiei of the Ecole Polytechnique Federale de Lausanne in Switzerland has revealed something very interesting about them. It appears that they formed under conditions of extreme pressure – the kind of pressure that would be found at the boundary between the core and the mantle of a Mars-sized planet.

There would seem to be no way that something that formed this deep inside, say, Mars or Mercury could somehow escape into interplanetary space. What we are seeing, then, is a relic from a Mars-sized world that no longer exists.

From our various studies of the process by which the planets in our solar system formed – studies that include both geological analysis of the worlds within the solar system as well as astronomical studies of the planet-forming sites around other stars – we’ve learned that a significant number, probably dozens, of such worlds inhabited the inner solar system during the first 10 million years or so of its existence.

This was a very violent time in our solar system, with these various worlds sometimes colliding with each other, but the eventual result was the four planets of the inner solar system that we have today, plus Earth’s moon.

The small asteroid that, billions of years later, would become known as 2008 TC3 and then as the Almahata Sitta meteorite, apparently began deep within the interior of one of these lost worlds. During a collision between that world and another similar object, that small chunk of rock was blasted free – along with many other such chunks, of course.

It roamed the inner solar system for over 4 billion years before eventually meeting up with our planet Earth.

In doing so, it has provided us with some tantalizing glimpses into a violent past that is radically different from our relatively sedate present. It has also provided us a small glimpse into the history of an entire world that has long since vanished down the corridors of time.

Alan Hale is a professional astronomer who resides in Cloudcroft. Hale is involved in various space-related research and educational activities throughout New Mexico and elsewhere.