Ring around a dwarf planet

Subject: Science and technology

Section: Space technology

Concept:

Astronomers have found a ring around a dwarf planet, located in the Kuiper Belt at the solar system’s edge, called Quaoar, according to a new study.
The ring, however, is positioned much further away from the planet than is usual and defies theoretical explanations.

Quaoar dwarf planet

With an estimated radius of 555 km, Quaoar is roughly half the size of Pluto and orbits beyond Neptune.
It also has a moon of its own, which is known as Weywot.
As the dwarf planet is too small and too distant to be observed directly, the researchers detected the ring with the help of a phenomenon called stellar occultation.

Occultation

An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The term is often used in astronomy.
If the closer body does not entirely conceal the farther one, the event is called a transit.
Both transit and occultation may be referred to generally as occlusion; and if a shadow is cast onto the observer, it is called an eclipse.
The term occultation is most frequently used to describe those relatively frequent occasions when the Moon passes in front of a star during the course of its orbital motion around the Earth.

How was the ring discovered?

A stellar occultation occurs when, as seen from Earth, a bright star passes behind a planet.
This allows astronomers or anybody on Earth to observe the sharp silhouette of the planet for a brief period of time.
The phenomenon, which rarely occurs, is used by researchers to analyze a planet’s atmosphere and determine if it has a ring around it — in 1977, scientists discovered the Uranian ring system with the help of stellar occultation.

Roche limit

Located 2,500 miles away from the dwarf planet, the ring is around 1,400 miles further away from the Roche limit, as per the calculations of the scientists.
It suggests that at such a distance, the particles of the ring should have come together to form a moon.
Roche limit refers to the distance from any celestial body within which its tidal forces prevent the formation of natural satellites.
Material in orbit outside the Roche limit would be aggregating to become natural satellites.
The rings of other planets lie within the Roche limit.

Earth and Moon Example

For a further understanding of the Roche limit, let’s look at the Earth and the moon. The Earth’s gravity pulls on the moon.
However, one side of the moon is closer to the planet and hence, the pull is stronger on the side facing the Earth.
The result is the so-called tidal force, which either stretches or compresses the moon from all sides.

What is the reason behind Quaoar’s far-out ring?

As of now, nobody exactly knows how Quaoar’s ring has managed to remain stable at such a distance from the Roche limit.
The researchers said that there can be a variety of possible explanations but they aren’t sure about any one of them.
It might be possible that Quaoar’s moon, Weywot, or some other unseen moon contributes gravity that somehow holds the ring stable.
Another potential explanation can be that the particles of the ring are colliding with each other in such a way that they are avoiding to coalesce into a moon.