Centaurs are real. In space, that is. These celestial objects orbit the sun between Jupiter and Neptune and have the characteristics of both asteroids and comets. Now, astronomers are learning more about a famous centaur known as (2060) Chiron and how its surface chemistry sets it apart from other centaurs, by detecting its chemical composition for the first time. Chiron has both carbon dioxide and carbon monoxide ice alongside carbon dioxide and methane gases in the cloud-like envelope of dust and gas that surrounds it–called a coma. The findings are detailed in a study published December 18 Astronomy & Astrophysics and add understanding the make up of these objects that date back to our Solar System’s early days.
This new study also builds upon a discovery from earlier this year that detected carbon monoxide and carbon dioxide ice on trans-Neptunian objects (TNOs) for the first time.
Comets vs asteroids vs centaurs
Both comets and asteroids are planetary objects that orbit the sun, but they do have some key differences.
According to NASA, an asteroid like Dimorphos is a small, rocky object that appears as a point of light when observed with a telescope. Most asteroids are found in the asteroid belt–a ring between the orbit of Mars and Jupiter. They also come in various shapes and sizes and some have a satellite orbiting.
A comet, such as Halley’s comet, is made out of ice and dust. When a comet near the sun, its dust and ice begins to vaporize. When viewed with a telescope, a comet appears fuzzy and like it has a tail as the vapor trails it.
[ Related: Dinosaur-killing asteroid likely came from deep space beyond Jupiter. ]
Much like the mythological half-human and half-horse creatures, centaurs in space have characteristics of both comets and asteroids. They revolve around the sun in the outer solar system, primarily between the orbits of the gas giant Jupiter and Neptune.
In 1977, Chiron became the first centaur ever discovered. Astronomers originally thought that it was an asteroid, but when it was seen emitting a halo of gas and a tail like a comet, they realized it was not a space rock. Chiron is even an oddball among these hybrid celestial bodies, as it sometimes acts more like a comet with rings of material around it.
Finding Chiron’s gas
In the new study, a team used data from the James Webb Space Telescope (JWST) to study these TNOs that are a bit like floating time capsules.
“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,” study co-author and planetary scientist Noemí Pinilla-Alonso told UCF Today. “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.”
Pinilla-Alonso is an Associate Scientist at UCF and now now works at the University of Oviedo in Spain.
With Chiron, astronomers can observe its surface where most of the ice is found and the coma where gases originate.
“TNOs 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,” said Pinilla-Alonso.
[ Related: Planet Nine might not actually be a planet. ]
Understanding which gases are in the coma and the different relationships with the ice can help us understand the chemical and physical properties at play. The JWST helped the team pinpoint the carbon dioxide and carbon monoxide ice alongside carbon dioxide and methane gases in Chiron’s coma.
“These results are like nothing we’ve seen before,” study co-author and UCF astrophysicist Charles Schambeau told UCF Today. “Detecting gas comae around objects as far away from the Sun as Chiron is very challenging, but JWST has made it accessible. These detections enhance our understanding of Chiron’s interior composition and how that material produces the unique behaviors as we observe Chiron.”
The JWST’s spectra data also showed the huge amount of various ices with different volatilities and how they are made. Chiron likely originated from the TNO region and has likely been zipping around our Solar System since it was formed about 4.6 billion years ago. The team hopes to continue analyzing Chiron’s gases in the future.
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