DWARF PLANET

1. Context

2. Dwarf Planet

• A dwarf planet is a small planetary-mass object that is in direct orbit of the sun, smaller than any of the eight classical planets but still a world in its own right.
• The prototypical dwarf planet is Pluto. Astronomers are in general agreement that at least the nine largest candidates are dwarf planets: Pluto, Eris, Haumea, Makemake, Gonggong, Quaoar, Sedna, Ceres, and Orcus.

3. A recent discovery about Quora

• Recently, a ring system or a clumpy disc of ice particles was observed around Quaoar, at a distance of 4,100 Km from its center.
• Quaoar is a dwarf planet, about half the size of Pluto, located in the Kuiper belt, which is a region of icy planetesimals beyond Neptune.
• The planet was discovered in 2002 and has been defined as a minor planet, as the International Astronomical Union has yet to formally classify it as a dwarf planet.

4. 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.
• This 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 Uranium ring system with the help of stellar occultation.
• The team involved in the latest study examined Quaoar for around three years, between 2018 and 2021, through Earth-based and space-based telescopes.
• During these years, the dwarf planet passed in front of four stars, helping researchers observe the shadow of the eclipses.

5. Roche Limit

• 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.
• They suggest that at such a distance, the particles of the ring should have come together to form a moon.
• 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 helps the moon keep it together is its own gravity. It essentially counteracts the effect of the tidal force.
• But if you bring the moon closer to the Earth, the tidal force will overcome the satellite's gravity and then disintegrate it, turning the moon into a ring.
• The minimum distance at which this happens is known as the Roche limit. It is named after the French astronomer Edouard Roche, who discovered the limit in 1848.
• The Roche limit does not just exist between just the Earth and the Moon. It 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.

6. 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 of the study have 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 to 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.
• No matter what the reason, astronomers believe 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.

For Prelims