Using Forrest Gump’s famous manipulated phrase, the The universe is like a box of chocolates, you never know what you’re going to find. In this case, pointing the James Webb Space Telescope, rings of water ice were discovered around the asteroid Chariklo.
NASA scientists used a high-precision observational feat to capture the starlight shadows cast by the asteroid’s thin rings.
10199 Chariklo, discovered on February 15, 1997, was the first asteroid found with a ring system. It was the fifth ring system found in our solar system - after Saturn, Jupiter, Uranus and Neptune.
At about 302 kilometers in diameter, Chariklo is the largest member of a class of asteroids known as the Centaurs. This rock orbits between Saturn and Uranus in the outer solar system.
James Webb offers another level of space studies
The feat was made possible by James Webb's Near-Infrared Camera (NIRCam) instrument. The discovery was based on a phenomenon called occultation, which is when a celestial body passes in front of a star and blocks its light.
The highlight of this observation is Chariklo and its rings. As mentioned earlier, this is the largest asteroid centaur in the Solar System, located more than three billion kilometers away beyond the orbit of Saturn. Its size is about 250 kilometers in diameter.
As it passed the star Gaia DR3 6873519665992128512 and with the occultation effect, it was revealed that the rings orbiting Chariklo are composed of small particles of water ice mixed with dark matter, which are likely debris from an icy body that collided with the asterite Past.
This is Webb's 1st look at a stellar occultation (when a foreground object passes in front of a star from our perspective on Earth). The moving object here is Chariklo, a small icy body between Saturn and Uranus, and the star is in the center. https://t.co/OOsXZ3z5sq pic.twitter.com/EAmLSaEyNt
— NASA Webb Telescope (@NASAWebb) January 25, 2023
These rings are very thin and are located at a distance of about 400 km from the center of the body. The discovery was made by Pablo Santos-Sanz of the Institute of Astrophysics of Andalusia in Granada, Spain.
As we dig deeper into the data, we will investigate whether we have cleanly resolved the two rings. From ring occultation light curve shapes, we'll also explore ring thickness, particle sizes and colors, and more. We hope to gain insight into why this small body has rings and perhaps detect new, fainter rings.
Are they really asteroids?
These bodies are categorized as asteroids, but while most asteroids lie in the asteroid belt between Mars and Jupiter — closer to the Sun — the Centaurs may come from the Kuiper Belt, described as a rotating disk in the outer Solar System. it extends from the orbit of Neptune at 30 astronomical units (AU) to about 50 AU from the Sun.
Centaurs have erratic orbits that cross the orbits of giant planets. Chariklo's orbit looks to that of Uranus. Because their orbits are often perturbed, Centaurs like Chariklo are expected to remain in their orbits for only millions of years, unlike our Earth and other large planets that orbit our Sun for billions of years.
The new computer visualization suggests that the particle density of the Chariklo ring should be less than half the density of Chariklo itself. And they show a striated pattern that forms in the inner ring due to interactions between particles. They use the term "awakened self-gravity" for this pattern.
So what we see with Chariklo and his ring system is probably a very temporary and dynamic situation. Things in space tend to happen on much longer timescales than we humans are used to, but sometimes things happen on human timescales. Chariklo rings can be an example!