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Roche limit and planetary rings

2023 FEB 20

Preliminary   > Geography   >   Cosmology   >   Cosmology

Why in news?

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

About Quaoar:

  • 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.

What is stellar occultation?

  • 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.

 New findings defy Roche limit:

What is Roche limit/Roche radius?

It is the distance from a celestial body within which a second celestial body, held together only by its own force of gravity, will disintegrate because the first body's tidal forces exceed the second body's self-gravitation.

Inside the Roche limit, orbiting material disperses and forms rings, whereas outside the limit, material tends to coalesce. The Roche radius depends on the radius of the first body and on the ratio of the bodies' densities.

  • The most intriguing part of the findings is 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.
  • It suggests that at such a distance, the particles of the ring should have come together to form a moon.

 

PRACTICE QUESTION:

‘Roche limit’, sometimes seen in news, refers to:

(a) The range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure

(b) The minimum distance to which a large satellite can approach its primary body without tidal forces overcoming the internal gravity holding the satellite together
(c) A critical mass below which an astronomical object cannot sustain its surface luminosity through nuclear fusion.

(d) The imaginary great circle of a body's celestial sphere that is coplanar with the body's terrestrial equator.

Answer

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