Hypatia: A stone older than the solar system

Popular Mechanics takes a long look at what, at first glance, might easily be dismissed as another Egyptian desert pebble – but is, in fact, a meteorite fragment older than our planet, or even our solar system:

Named for Hypatia of Alexandria, the first prominent Western woman astronomer and mathematician, the colorful rock was found in 1996 in western Egypt by Aly Barakat, a geologist working for the Egyptian Geological Survey. Barakat was studying Libyan desert glass, which appears to be similar to sea glass from the ocean, except geologists believe it might have formed roughly 28 million years ago in a meteorite impact.

Barakat immediately recognized the unique significance of the glossy stone, lined with microscopic diamonds, and he suspected that it did not come from Earth. In 2013, geologists studying the Hypatia stone confirmed the rock was of extraterrestrial origin. Unlike any known meteorite, researchers originally believed the Hypatia stone was the first sample of a comet nucleus.

But it seems the space rock has a much more interesting past. A new study led by geologists at the University of Johannesburg found that compounds in the Hypatia stone are distinct from anything discovered in the solar system. The researchers therefore conclude that parts of the rock formed before the solar system, and if these compounds are not presolar, the prevailing idea that the solar system formed from a nebula of homogenous gas is called into question.

Using sophisticated electron microscopy to determine the compositions of microscopic parts of the Hypatia stone, [Jan] Kramers and fellow geologists at the University of Johannesburg identified the parts of the rock that were not added when it impacted Earth. They found that many compounds in the stone seem to have formed prior to the sun and planets. The elements are the same—carbon and silicon and aluminum and iron—but the ratios of these elements in the material are all wrong, unlike the compositions of objects that orbit the sun.

In other words, most of the rock in the Hypatia stone has the opposite ratio of carbons to silicons that you find in the vast majority of the asteroid belt as well as the planets Earth, Mars, and Venus. Not only that, but the mineral matrix of Hypatia also contains a significant amount of interstellar dust not generally seen in the rocky stuff of the solar system.

“Even more unusual, the matrix contains a high amount of very specific carbon compounds, called polyaromatic hydrocarbons, or PAH, a major component of interstellar dust, which existed even before our solar system was formed,” says Kramers. “Interstellar dust is also found in comets and meteorites that have not been heated up for a prolonged period in their history.”

These polyaromatic hydrocarbons are the the components of the stone that turned to diamond from the heat and pressure of entering Earth’s atmosphere and then impacting the Sahara Desert. This protective layer of space diamonds has helped Hypatia last so long, preserving the rock for geologists to study today.