A small extraterrestrial pebble, which was previously discovered in south-west Egypt, continues to baffle scientists as it has been found to contain micro-mineral compounds that are apparently not from the solar system.
Scientists announced back in 2013 that the stone, dubbed the "Hypatia stone," didn't have any Earthly origin. Subsequent analysis revealed that the stone was not even from any known types of meteorite or comet.
As part of the new study, researchers at the University of Johannesburg performed micro-mineral analyses of the pebble to discover that it lacked silicate matter, setting it apart from interplanetary dust particles and comets that have fallen to Earth.
What makes it even more intriguing is the presence of minerals that seem to predate the Sun, scientists said in the study, published recently in the journal Geochimica et Cosmochimica Acta.
The researchers have compared the stone's internal structure to that of a fruitcake that has fallen off a shelf into some flour and shattered.
"We can think of the badly mixed dough of a fruit cake representing the bulk of the Hypatia pebble, what we called two mixed 'matrices' in geology terms," Jan Kramers, lead researcher of the study, said in a statement.
"The glace cherries and nuts in the cake represent the mineral grains found in Hypatia 'inclusions'. And the flour dusting the cracks of the fallen cake represent the 'secondary materials' we found in the fractures in Hypatia, which are from Earth," Kramers said.
It was Hypatia's weird composition that stunned the researchers the most. According to them, it has a massive amount of carbon and an unusually small amount of silicon unlike non-metallic chondritic meteorites that are rice in silicon with a small amount of carbon.
"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," Kramers said.
Another strange aspect of Hypatia is that most of the PAH in the stone transformed into diamonds smaller than one micrometer. Scientists believe that these diamonds were formed when the stone hit the Earth's atmosphere or surface.
That's not all about the odd traits of the stone. Analysis of the mineral grains in Hypatia revealed aluminium in its pure metallic form, something that is extremely rare on Earth and the rest of our solar system.
In addition, the researchers also found silver iodine phosphide and moissanite (silicon carbide) grains "in highly unexpected forms," and grains of a compound consisting of mainly nickel and phosphorus, with very little iron. According to researchers, the mineral composition of the latter compound has never been observed on Earth or in any known meteorite.
"What we do know is that Hypatia was formed in a cold environment, probably at temperatures below that of liquid nitrogen on Earth (-196 Celsius). In our solar system it would have been way further out than the asteroid belt between Mars and Jupiter, where most meteorites come from," Kramers said.
"Comets come mainly from the Kuiper Belt, beyond the orbit of Neptune and about 40 times as far away from the sun as we are. Some come from the Oort Cloud, even further out. We know very little about the chemical compositions of space objects out there. So our next question will dig further into where Hypatia came from," Kramers added.