It’s a bird! It’s a plane! No, it’s an asteroid-comet hybrid called a ‘centaur’ that might not even be that.
Asteroids are metallic rocks that form close to the sun, while comets are dirty snowballs thrown from the fringes of our star system.
Then there’s whatever the heck 2006 Chiron is.
Chiron is a class of comet-ish asteroids/asteroid-ish comets called centaurs – named after the half-human, half-horse hybrid – found bouncing between Jupiter and Neptune.
But Chiron is an ‘oddball when compared to the majority of other centaurs,’ said physicist Charles Schambeau of the University of Central Florida.
‘It has periods where it behaves like a comet, it has rings of material around it and potentially a debris field of small dust or rocky material orbiting around it.
‘So, many questions arise about Chiron’s properties that allow these unique behaviours.’
Centaurs are the dinosaur bones of the solar system, made up of the same dust and gas that formed the solar system 4.5 billion years ago.
‘All the small bodies in the solar system talk to us about how it was back in time, which is a period of time we can’t really observe anymore,’ said UCF scientist Noemí Pinilla-Alonso.
‘But active centaurs tell us much more. They are undergoing transformation driven by solar heating and they provide a unique opportunity to learn about the surface and subsurface layers.’
Chiron, in other words, is like finding a T-Rex fossil that has a pair of wings and could help explain how our star system came to be. But because it’s so far away, it’s made learning about it hard.
So UCF researchers used the James Webb Space Telescope to work out what it’s made from for the first time since its discovery in 1977.
‘Discovering which gases are part of the coma and their different relationships with the ices on the surface help us learn the physical and chemical properties, such as the thickness and the porosity of the ice layer, its composition, and how irradiation is affecting it,’ said Pinilla-Alonso.
Unlike other centaurs, Chiron’s surface has carbon dioxide and carbon monoxide ice as well as carbon dioxide and methane gases in its wispy shell known as a coma.
These substances aren’t too interesting on their own, but together on an object as far-flung as Chiron is ‘unique’, the researchers said.
Using a term for minor planets beyond Neptune, Pinilla-Alonso added: ‘[Trans-Neptunian Objects] don’t have this kind of activity because they’re too far and too cold.
‘Asteroids don’t have this kind of activity because they don’t have ice on them.
‘Comets, on the other hand, show activity like centaurs, but they are typically observed closer to the sun, and their comas are so thick that they complicate the interpretations of observations of the ices on the surface.’
The findings, published in Astronomy & Astrophysics last month, are ‘like nothing we’ve seen before’, said Schambeau.
His team hopes to observe Chiron more as it moves closer to Earth to give us more clues about these weird rocks.
And the clock is ticking. Centaurs only whizz around for a few million years before falling into a planet or drifting towards the sun and becoming comets.
‘“Every active centaur that we are observing with JWST shows some peculiarity. But they cannot be all outliers,’ added Pinilla-Alonso.
‘There must be something that explains why they appear to all behave differently or something that is common between them all that we cannot yet see.’
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