In 2008, something unique fell from the sky over Sudan, exploding in fragments along the vast and arid expanses of the Nubian desert.
This hard object from above became known as the Almahata Sitta: a collection of about 600 meteorite fragments, carefully recovered by researchers and which takes its name – “Station Six” – from a nearby station.
What was unique about the Almahata Sitta is that it represented something unprecedented in astronomy: the first time an asteroid was successfully anticipated in advance by scientists.
Since then, the chips of that asteroid – called TC3 in 2008 – have been analyzed by researchers, looking for chemical clues about the origins of this mysterious and distant visitor.
Now, a new study highlights that intriguing story.
Fragment AhS 202. (Muawia Shaddad)
Looking at the chips, he can tell us about TC3 2008, which in turn can tell us about where TC3 2008 came from – like an astronomical chain of nesting Matryoshka dolls.
“Our surprising result suggests the existence of a large, water-rich parent body,” says first author and planetary geologist Vicky Hamilton of the Southwest Research Institute in Boulder, Colorado.
In the new paper, Hamilton and his research colleagues did not have much work to do, analyzing only the smallest of the pieces of this remarkable space rock.
“We were given a 50 milligram sample of Almahata Sitta for study,” says Hamilton. “I mounted and polished the small fragment and used an infrared microscope to examine its composition.”
Spectral analysis revealed something that scientists did not expect to find. Inside the fragment – a fragment called AhS 202 – was found an extremely rare form of hydrated crystal, known as an amphibole.
This type of mineral requires prolonged bursts of heat and extreme pressure to form, a type that is not usually thought to be possible in carbonic chondrite (CC) meteorites.
Micrograph showing amphibole crystals in orange. (NASA / USRA / Lunar and Planetary Institute)
The implications suggest that the 2008 TC3 most likely belonged to a much larger body – something so large, in fact, that it would be practically in the same class as Ceres: the dwarf planet, which is the largest known object in the main belt. of asteroids, between the orbits of Mars and Jupiter.
“It is believed that most parent CC bodies are less than 100 km in diameter and therefore would not be large enough to produce the range of pressure and temperature conditions represented by the mineral assembly in AhS 202,” the authors explain in their paper their.
“As such, our interpretation is that the original parent body of the AhS 202 was probably an unknown object, potentially the size of Ceres (~ 640-1,800 km in diameter in the most probable conditions).”
While it is believed that this mysterious giant asteroid no longer exists, the fact that it once inhabited our solar system suggests that more of this kind could have done the same thing, even if we found no evidence of these large, water-rich bodies. in meteorite fragments recovered before TC3 in 2008.
In the same way that the asteroids Ryugu and Bennu reveal some surprises in composition that differ from most known meteorites, the multiple chips of TC3 in 2008 show that there are more space rocks than current hypotheses can fully explain.
“We do not propose that AhS 202 is a spectral analogue for Bennu or Ryugu; rather, AhS 202 is a serendipitous source of information about early Solar System materials that are not represented by whole meteorites in our collections,” the researchers conclude.
“The difference between its mineralogy and that of known CC meteorites suggests that unique samples such as AhS 202 (and xenoliths in other non-CC meteorites) could be crucial missing links in understanding the diversity of parent asteroids.”
The findings are reported in Nature Astronomy.