Dwarf Planets: Pluto, Ceres, and Beyond
By Yagyasha
Cosmofluencer (Season 04)
We all remember being spammed with memes about Pluto being “demoted” to a dwarf planet back in time. But was it truly ever downgraded or just given a new better fitting title? Let’s learn what dwarf planets are and then decide.
What are they?
On 24 August 2006 , members of the International Astronomical Union (IAU) voted unanimously to change the status of Pluto and its neighbor Eris as dwarf planets. The union reclassified these planets as “Dwarf Plants” citing that they did not meet the criteria to be defined as full-sized planets. Here is how IAU defines dwarf planets:
1. Celestial body that orbits the sun
2. Has a nearly spherical shape
3. The body has not cleared its orbit of other mass.
4. The body is not a satellite.
Hence, the main difference between full sized and dwarf planets is that the former can dominate their orbit. Full-sized planets have larger gravity and possess the ability to clear their orbit around the sun of any debris.
However, if these planets are their own separate entities or just another classification is going to be a hot debate for ages.
The Five Dwarfs of our Solar System
Currently there are 5 dwarf planets recognised by the International Astronomical Union(IAU). Let’s learn more about them. Apart from Eris and Pluto , three more planets are known to be the dwarfs of our solar system. These planets ranked by size are Eris, Pluto, Haumea, Makemake and Ceres. Each of them is more unique than the other. Here is what you need to know about each of them.
Fig: The five dwarf planets of our Solar System( https://science.nasa.gov/wp-content/uploads/2023/07/dwarf-planets.jpg?w=1920 )
ERIS: The One Who Started it All
After its discovery in 2005, Eris started the debate that led to reclassification of Pluto and others to Dwarf Planets in 2006. Name after the Greek goddess of Discord and its moon named Dynomia, the demon goddess of lawlessness. Eris is held guilty for the demotion of Pluto.
Eris is a cold world situated a large distance away from us beyond the orbit of Neptune. It is a part of Kuiper Belt which contains many icy worlds and are also termed as Plutoids. These were some of the earliest objects formed in the solar system. This dwarf is smaller than our moon and is so far away from sun that its atmosphere freezes and falls as ice.
Some Fun Facts about Eris:
1. Eris was originally named after a fictional character Xena, from Xena:Warrior Princess.
2. All the objects in the Asteroid Belt could fit inside Eris.
3. Eris takes about 557 earth years to orbit the sun, but approximately only 25.9 hours to complete a rotation.
Fig:Eris(https://www.earth.com )
PLUTO: The Star of the Dwarfs
This former planet is a mysterious icy world located in the kuiper belt. Pluto is filled with high mountains ,deep valleys, and large craters. Discovered in 1930 by Clyde W. Tombaugh, Pluto became the first known object in the Kuiper Belt.
This icy body is only about 1400 miles wide making it smaller than the United States. It is placed about 3.6 million miles away from the Sun and has a very thin atmosphere. This atmosphere is composed of nitrogen, methane and carbon monoxide. Average temperature of Pluto is about -232°C, making it inhabitable for us.
IAU reclassified this planet as a Dwarf planet in 2006, stating that since it lies in the Trans-Neptunian region its orbit is crossed by other objects.
Some Fun Facts about Pluto:
1. Pluto was named by an 11 year old girl, Venetia Burney.
2. One-third of Pluto’s surface is covered with water.
3. Pluto has been visited by only one spacecraft, New Horizons, in 2006.
CERES: The Dwarf Next Door
This rocky dwarf is the closest one to our planet and the only one present in the inner solar system. Ceres was discovered by Giuseppe Piazzi in 1801 making it the first object in asteroid belt to be discovered. Ceres has proved to be a puzzle right from its discovery, first we were sure it was a planet, but then scientists named it an asteroid due to its small size. Lastly, in 2006, alongside Pluto, it was finally classified as a dwarf planet.
In 2015, Ceres was visited by NASA’s spacecraft Dawn and it revealed a 57-mile-wide crater (now named Occator). This crater however was not ice as expected but a large sodium carbonate deposit that was formed when briny water gurgled up on ceres’ surface and sublimated. Ceres has always been a curious case for astronomers, more so because it is the only place near home that has water and potentially life!
Some Fun Facts about Ceres:
1. Ceres gets its name from the Roman goddess of corn and harvest. The word ‘Cereal’ also has similar origins.
2. Ceres accounts for one-third of the mass of asteroid belt.
3. It is the only dwarf without any moons.
MAKEMAKE: The Easter Egg
MakeMake, named after the RapaNui(mythology of Easter Island) goddess of Fertility, makemake was discovered the same day as Eris at Palomar Observatory by Mike Brown and his team. It too shared the blame(or credit) for dwarf planets.
MakeMake is an icy world located in the donut shaped belt called the Kuiper belt alongside Eris, Pluto and Haumea. It is about 444 miles in radius and takes about 305 years to orbit around the sun. This wondrous planet reflects about 95% sunlight it receives.
It was classified as a dwarf by IAU on the basis of its orbit and size.
Some Fun Facts about MakeMake:
1. MakeMake’s unofficial nickname was EasterBunny.
2. In 2016, a small dark moon was spotted near it by the Hubble Telescope.
HAUMEA: Strangest of Them All
Haumea is an intriguing world that resides alongside other dwarfs in the Transneptunian region. This small icy world is shaped like a rugby ball or an american football due to its fast spinning speed. Despite its small size it manages to have a saturn-like ring system of asteroids around itself.In addition, two moons of this tiny planet have been discovered.
It was discovered just a day after Eris and MakeMake and played an instrumental part in our understanding of our own solar system.
Haumea is the fastest rotating object in our solar system. According to NASA, it is possible that a large moving object may have collided and set Haumea in motion.
Some Fun Facts about Haumea:
1. Haumea was named after the Hawaiian Goddess of fertility
2. It was nicknamed Santa upon discovery due to its appearance.
3. It completes one rotation on its axis in just 4 hours.
Final Thoughts
This brings us to an end of discussion about the current dwarf planets. But thats not all, scientists believe there are a hundred more dwarfs in our neighborhood waiting to be discovered. Some promising names are Sedna, Quaoar and DeeDee. Object 2012 VP113, is also of interest and is estimated to have an orbit that stretches beyond the reaches of our solar system.
With this, here are some recommended reads to further quench any curiosity about these tiny worlds.
References
1. Ceres Facts | Space Facts
2. Ceres: The closest dwarf planet to Earth | Space.com
3. Dwarf Planets – Definition & Detailed Explanation – Planetary Science Glossary | Sentinel Missions
4. Dwarf Planets: All Dwarf Planets List in Order | Planets Education
5. Dwarf Planets: Science & Facts About the Solar System’s Smaller Worlds | Space.com