Astronomers have spotted a ring of Saturn-like debris around a Pluto-sized dwarf planet that they didn’t think was possible.
The researchers say their discovery defies current understanding of where such rings could form — because it’s farther away from smaller distant worlds than current scientific understanding allows.
The ‘unusual’ ring surrounding the dwarf planet Quaoar, which sits beyond Neptune, raises questions about how such systems form.
‘We observed a ring that shouldn’t be there,’ says Bruno Morgado of the Federal University of Rio de Janeiro.
The ring’s distance from Quaoar puts it at a point where scientists believe particles should coalesce around a celestial body to form a moon, rather than remaining as separate components in a disk of ring material.
‘Unusual’: Astronomers have spotted a ring of Saturn-like debris around a Pluto-sized dwarf planet they didn’t think was possible. Ring of Quaoar is an artist’s impression image
Why are choir rings so unusual?
Ring systems are relatively rare in the Solar System, and as well as around Saturn, Jupiter, Uranus and Neptune, there are only two small planetary rings – Chariklo and Haumea.
All previously known ring systems are able to survive because they orbit close to the parent body.
According to astronomers, what makes the ring system around Quire remarkable is that it lies more than seven planetary radii away—twice as far as what was previously thought to be the upper limit, the outer limit of ring systems. was considered viable.
The discovery therefore forced a rethinking of the theory of ring formation.
The discovery was made by an international team of astronomers using HyperCam – a highly sensitive high-speed camera developed by scientists at the University of Sheffield.
It is mounted on the world’s largest optical telescope, the 10.4 meter diameter Gran Telescopio Canarias in La Palma.
Because the rings are too faint to see directly in an image, the discovery was made by observing an occultation—when light from a background star is blocked by the quasar as it orbits the Sun.
Identified in 2002, Quaoar is currently defined as a minor planet and proposed as a dwarf planet, although it has not yet been officially given that status by the International Astronomical Union, the scientific body that conducts such work.
Its diameter of about 700 miles (1,110 km) is about a third that of Earth’s moon and half that of dwarf planet Pluto.
Earth has a small moon named Weywot, son of Quaoar in mythology, orbiting outside the ring 105 miles (170 km) in diameter.
Inhabiting a distant region called the Kuiper Belt populated by various icy bodies, Koar orbits about 43 times Earth’s distance from the Sun.
In comparison, Neptune, the outermost planet, orbits about 30 times Earth’s distance from the Sun and Pluto about 39 times.
Quaoar’s ring, a clumpy disk made of ice-covered particles, lies about 2,550 miles (4,100 km) from the planet’s center, with a diameter of about 5,100 miles (8,200 km).
Astronomer and co-author of the study Isabella Pagano said, ‘Ring systems may be due to debris from the same formation process that gave rise to the central body or may be due to material after colliding with another body and being captured by the central body.’
‘At the moment we have no clue as to how the Choir Ring was created.’
All previously known ring systems are able to survive because they orbit close to the parent body. But Quaoar’s remains are twice as far as what was previously thought to be the maximum limit, known as the Roche limit (pictured).
Material in orbit outside the Roche limit is expected to coalesce into a moon
Unlike any other known ring around a cosmic object, Quaoar’s Roche lies outside the boundary.
It refers to the distance from any celestial body possessing an appreciable gravitational field at which a nearby object would be separated.
Material in orbit outside the Roche limit is expected to coalesce into a moon.
Saturn has the largest ring system in our solar system.
The other large gas planets – Jupiter, Uranus and Neptune – all have rings, although less impressive, as do non-planetary bodies like Chariclos and Haumea. All remain within Roche limits.
So how does Quaoar violate this rule?
‘We considered some possible explanations: a ring made of debris, resulting from a disruptive impact on a quasar moon, would survive for a very short time – but the probability of observing it is extremely low,’ said Pagano.
‘Another possibility is that theories of ice particle aggregation need to be revised, and the particles may not always aggregate into larger bodies as quickly as one might expect.’
The discovery was published in the journal Nature.