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Ring around a Dwarf Planet: What is the Roche limit?

Feb 16, 2023

Ring around a Dwarf Planet What is the Roche limit

Today’s edition of our Current Affairs will comprise a discussion on Ring around a Dwarf planet: What is the Roche limit?. Read further to upgrade your UPSC CSE knowledge and also understand the topic’s relevance to the UPSC syllabus.

For Prelims: General Science

dwarf planet, Roche limit, Astronomers, Kuiper Belt, Quaoar

For Mains: GS Mains Paper III (Awareness in the field of Space)

Highlights of the study, About the Ring discovered, About the Roche limit, Reason behind Quaoar’s far-out ring


Recently a new study has said that Astronomers have found a ring around a dwarf planet, located in the Kuiper Belt at the solar system’s edge, called Quaoar.

Probable Question:

Elucidate the concept of Dwarf Planet, with latest findings. (150 words, 10 marks)

Highlights of the study:

  • It has been found that a dense ring of the trans-Neptunian object Quaoar is positioned much further away from the planet than is usual and defies theoretical explanations.
  • According to the study, the ring lies far away from the Roche limit, a mathematically determined distance beyond which rings aren’t supposed to exist.

Kuiper Belt:

The Kuiper Belt is a ring of icy bodies just outside of Neptune’s orbit. Pluto is the most famous Kuiper Belt Object (KBO). 

The Kuiper Belt is named after a scientist named Gerard Kuiper.


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. 

About the Ring discovered

  • When a star passes in front of a planet as seen from Earth, this is known as a stellar occultation. 
  • As the dwarf planet is too small and too distant to be observed directly, the researchers detected the ring with the help of stellar occultation.
  • Stellar occultation makes it possible for astronomers or anybody on Earth to briefly glimpse the planet's distinct silhouette. 
  • Researchers use the infrequent occurrence to examine a planet's atmosphere and determine whether it has a ring system around it. For example, in 1977, scientists used stellar occultation to make the discovery of the Uranian ring system.
  • Between 2018 and 2021, the research team behind the most recent study observed Quaoar using both terrestrial and extraterrestrial observatories. The dwarf planet helped scientists see the eclipses' shadows throughout these years as it passed in front of four stars.
  • Nevertheless, scientists also noticed some brightness decreasing both before and after the star blinked out. This indicated a ring that obscured some of the light.
Ring around a Dwarf planet: What is the Roche limit?

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About the Roche limit

  • Roche limit is named after the French astronomer Édouard Roche, who discovered the limit in 1848.
  • The moon is pulled towards the Earth by gravity. The draw is stronger on the side facing the Earth because one side of the moon is closer to the planet than the other. 
  • As a result, the moon is compressed or stretched from all sides by the so-called tidal force. However, the moon's own gravity aids in keeping it intact by negating the tidal force's effects.
  • The moon’s gravitational pull can be overpowered, if it is moved closer to the planet and it will eventually shatter the satellite, transforming it into a ring.
  • The Roche limit is the shortest distance at which this occurs.
  • The distance between Quaoar and its ring 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. 
  • They suggest that at such a distance, the particles of the ring should have come together to form a moon.
  • The Roche limit is applicable to any planet and the celestial bodies around it. For instance, Saturn. The beautiful rings that you see around the planet are within the Roche limit and therefore, there are no moons in that area.
  • In 1992, comet Shoemaker–Levy 9 got too close to Jupiter, breaching the Roche limit, and was broken apart by the tidal force. 
  • Two years later, parts of it collided with the planet, providing the first direct observation of an extraterrestrial collision of solar system objects.

Reason behind Quaoar’s far-out ring:

  • The researchers of the study have said that there can be a variety of possible explanations regarding Quaoar’s far-out ring, but till now they aren’t sure about any one of them.
  • The new study points to the possibility of discovering more rings around smaller planets like Quaoar in the outer solar system, which might expand our understanding of planetary ring systems.

News Source: The Indian Express


Frequently Asked Questions

What are dwarf planets?

According to the International Astronomical Union, which sets definitions for planetary science, a dwarf planet is a celestial body that -orbits the sun, has enough mass to assume a nearly round shape, has not cleared the neighborhood around its orbit, and is not a moon.

Which dwarf planet has a ring?

It has been found that Quaoar, a dwarf planet, has a dense ring of the trans-Neptunian object. Quaoar is positioned much further away from the planet than is usual and defies theoretical explanations. According to the study, the ring lies far away from the Roche limit, a mathematically determined distance beyond which rings aren’t supposed to exist.

Do dwarf planets have rings?

Yes, it was recently discovered that Quaoar, a dwarf planet, has a dense ring of the trans-Neptunian object.

Which planet is known for their splendid rings?

No other planet in our solar system has rings as splendid as Saturn’s. They are so expansive and bright that they were discovered as soon as humans began pointing telescopes at the night sky. Saturn is the most distant of the five planets known to ancient stargazers. In 1610, Italian Galileo Galilei was the first astronomer to gaze at Saturn through a telescope. 

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