A mysterious ring on a dwarf planet is puzzling astronomers

Quaoar, which revolves the Sun beyond Neptune, has a ring that is too far out according to current theories
Quaoar’s unique ring system, which are much further out than astronomers expected. Photo: Paris Observatory
Quaoar’s unique ring system, which are much further out than astronomers expected. Photo: Paris Observatory

Astronomers are puzzled by a dwarf planet in our solar system — about half the size of Pluto — with unusual rings, according to a new study. The dwarf planet orbits the Sun beyond Neptune.

The rings of Quaoar are positioned at a distance of over seven planetary radii — much further away from other planets that possess rings, noted the study published in Nature journal.

Saturn’s main rings, in contrast, are found within three planetary radii. The planetary radius is the distance between a planet’s centre and its surface.

“It was unexpected to discover this new ring system in our solar system, and it was doubly unexpected to find the rings so far out from Quaoar, challenging our previous notions of how such rings form,” Vik Dhillon, co-author of the study from the University of Sheffield’s Department of Physics and Astronomy, said in a statement.

Planetary rings possess small chunks of ice and other materials that orbit a larger object. Only Saturn, Jupiter, Uranus and Neptune, including two other minor planets, Chariklo and Haumea, are known to possess rings.

Some 59 researchers from across the world discovered the odd rings while studying distant objects in our solar system.

“My colleagues on the paper have been studying the objects in the solar system for many decades. So, this study is simply part of ongoing research into the area, trying to find out more about the most distant planets,” Dhillon told Down To Earth.

Dhillon and his colleagues studied these distant objects using an extremely sensitive high-speed camera mounted on the 10.4-metre diameter Gran Telescopio Canarias in Spain. They studied occultations, which occur when an object passes in front of another from an observer’s perspective. 

They found a dip in brightness as Quaoar blocked light from a background star. Additionally, they found two more dips. “The two dips were on either side of the main dip caused by Quaoar. So, this means there must be a ring system surrounding the planet,” Dhillon explained.

Using the time difference between the two dips and the main dip, the researchers estimated the distance of the rings from the planet. The rings’ position contradicts the ‘Roche limit’, which is the outer limit of where ring systems were thought to be able to survive.

The rings of other planets lie within the Roche limit. Tidal forces prevent the rings from aggregating to become natural satellites.

The question of why the rings of Quaoar have not coalesced into a satellite is not clear. But Dhillon speculated that this could be because the collisions between the ring particles are elastic due to their hard, icy surfaces.

“Everyone learns about Saturn’s magnificent rings when they’re a child, so hopefully, this new finding will provide further insight into how they came to be.”

Dhillon plans to study Quaoar further to reduce their findings’ uncertainty and investigate whether the ring changes properties with time.

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