In the far reaches of space, beyond the orbit of Jupiter, lurks a strange object. Its name is Chiron, a type of outer solar system body known as a centaur. But even among its fellow centaurs, Chiron is special—and new observations from JWST reveal just how truly unlike anything we’ve seen before, Chiron is.
“It’s a strange animal compared to most other centaurs,” says physicist Charles Schambeau of the University of Central Florida.
“It has periods where it behaves like a comet, has rings of material around it, and potentially a debris field of fine dust or rocky material orbiting around it. So there are a lot of questions about what properties Chiron has that allow for these unique behaviors.”
The solar system is littered with rocky and icy remnants from its formation some 4.5 billion years ago. Centaurs, which mostly reside between Jupiter and Neptune, with orbits that cross the paths of at least one of the giant planets, are an interesting set.
Chiron, for example, has properties similar to those of an asteroid, but it also sometimes exhibits comet-like activity. Oh, and it has a ring around it, like a miniature planetary ring.
Since Chiron is considered a sort of time capsule of the formation of the solar system, scientists are eager to learn more about this strange rock, but its distance makes it hard to understand.
Led by planetary scientist Noemí Pinilla-Alonso of the University of Oviedo in Spain, a team of researchers used the powerful eye of the JWST to see if it could see details that had previously eluded us.
“All small bodies in the solar system tell us about the past, which is a period of time that we can no longer observe,” says Pinilla-Alonso. “But active centaurs tell us much more. They are undergoing a transformation driven by solar heating, and they provide a unique opportunity to learn about the layers of the surface and subsurface.”
Sometimes, Chiron ejects gas and dust, as comets do. The researchers used JWST to try to see what this gas and dust is made of — not just what’s in the space around the centaur in what’s known as the coma (like a comet’s atmosphere), but what might be inside it.
“What’s unique about Chiron is that we can observe both the surface, where most of the ice can be found, and the coma, where we see gases that originate from or just below the surface,” says Pinilla-Alonso.
“Finding out which gases are part of the coma and their different relationships with the ice on the surface helps us learn about the physical and chemical properties, such as the thickness and porosity of the ice layer, its composition, and how radiation affects it.”
They took near-infrared observations and analyzed the spectrum for absorption and emission lines that result from the absorption and re-emission of light at specific wavelengths by specific atoms and molecules.
Similar observations in the past have revealed the presence of cyanide and carbon monoxide.
Pinilla-Alonso and his colleagues found carbon dioxide, carbon monoxide, ethane, propane, acetylene, methane and water ice. The detection of methane is particularly notable, the researchers say, with results suggesting that Chiron’s coma is full of it. There’s a joke somewhere about centaur farts, but we’re too mature to make it.
Scientists believe that centaurs were once members of an even more distant population of icy rocks in the solar system, the trans-Neptunian objects, or TNOs, which orbit the sun beyond the orbit of Neptune.
Because they are so far from the sun, TNOs are thought to be relatively pristine remnants of the solar system’s formation, encapsulating the early composition of the dust cloud from which the solar system was born.
As they approach the Sun, the ices on the centaurs may sublimate, releasing some of this material. The researchers believe that the methane, carbon dioxide, and water ice they observe on Chiron could be some of the pristine materials it inherited from the birth of the Solar System.
Other compounds, such as ethane, propane, and acetylene, may have formed on the centaur’s surface as a result of reduction and oxidation—that is, rust.
“Based on our new data from JWST, I’m not so sure we have a standard centaur,” says Pinilla-Alonso.
“Every active centaur we’re observing with JWST shows some peculiarity. But they can’t all be outliers. There must be something that explains why they seem to behave differently, or something that is common among all of them that we can’t see yet.”
The researchers plan to continue observing Chiron as it gets closer to us, to see if there is anything about the way it changes over time and seasons that gives more clues about the nature of these strange, icy, erupting rocks.
The research was published in Astronomy & Astrophysics.
Imagen (Equipe Celestia/Wikimedia Commons/GNU General Public License)
