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Wednesday 18 June 2014

Chariklo, the Celestial midget

In March, the European Southern Observatory in Chile made an astonishing discovery that has surprised astronomers. It’s no secret that the great gas giant, Saturn, has an impressive set of rings surrounding it - and while less widely known, in fact all Jovian planets (Neptune, Uranus, Jupiter and Saturn) have ring systems around them. These planets are the largest in our solar system, and have a tremendous gravitational pull on rocks, dust and gas due to their great size which keeps their ring structures in place. However, nestled between Saturn and Uranus, they’ve discovered a comparatively minuscule object with a fraction of the gravitational strength which has its very own rings - something many astronomers believed to be impossible.

Artist’s impression close-up of the rings around Chariklo
Artist’s impression of the asteroid Chariklo, and its newly discovered rings.
Image credit: ESO/L. Cal├žada/M. Kornmesser/Nick Risinger (

Chariklo 10199 is what’s known as a Centaur, an object which originates at the very limits of our Solar System (a region called the Kuiper Belt) and carries characteristics of both asteroids and comets. This particular Centaur is merely 250km wide, that’s roughly the same width as Lake Victoria in Africa and barely 0.0004% of Saturn’s volume, making it a celestial midget. It’s this midget which has been discovered to carry its own ring system made up of space dust and particles – just like the Jovian planets.

Why is it that this space boulder has rings too? How did they get there? What can they tell us about our Solar System?

To quote lead author Dr Felipe Braga-Ribas of the National Observatory in Brazil;
“Rings are natural laboratories in which to study dynamical processes analogous to those that take place during the formation of planetary systems and galaxies.”
In other words we can scrutinise the behaviour of rings like these and extrapolate that information to larger systems, like our Solar System or even the Milky Way, and further our understanding on how these huge structures came to be.

Additionally, infrared observations of Chariklo 10199 over the past decade have revealed what could be the presence of frozen water, now thought to be in it’s rings[1]. This has led to a number of possible conclusions about the Centaur’s past. Perhaps poor old Chariklo collided with another minor object, shattering its own icy crust and sending material flying into orbit. Larger fragments from this impact may now be the postulated shepherd moons which forced the rings to form as they did. Another idea is that perhaps two moons which once encircled Chariklo were involved in an almighty collision, reducing both satellites to dust and icy grains. It’s even suggested that Chariklo’s own gravitational power shredded a pre-existing moon, pulling it apart into the rings we see today. All of this has been constantly in debate, as some scientists speculated that water is not present at all, but this was before the discovery of Chariklo’s rings[2]. Careful analysis and observation of the Centaur and it’s rings behaviour should reveal the truth.

All things are possible. At the moment we simply don’t know. Astronomers are not even sure if this Centaur is an anomaly or going through a generic stage in its life typical of all similar objects. The knowledge gained from Chariklo’s rings is invaluable in giving us an exclusive insight into formations of planetary systems. Furthermore, Chariklo is just the beginning – 183 Centaurs have been seen and over 44,000 are estimated to exist, each of which could possibly hold another piece of the puzzle which is our Solar System.

why don't all references have links?

[1] Braga-Ribas F., Sicardy B., et al “A Ring System Detected around the Centaur (10199) Chariklo” Nature 508, 72-75 (2014). DOI:10.1038/nature13155
[2] Guilbert A., Barucci M.A., et al “Near-Infrared Spectra of TNOs: First results of the new ESO-large program and Implications” Science of Solar System Ices (2008)

This article was written by our summer 2014 physics internGrace Mason-Jarrett.

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