Back when we were in school there were 9 planets in the solar system: – Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune & Pluto. But now there are only 8 planets in the solar system. What happened? Who dropped out? Yah its Pluto, but why?
Well, it all changed after the discovery of Eris by Mike Brown. In 2006 scientists started to speculate whether Pluto is a Planet or not. Pluto was demoted as a planet in 2006 when a group of scientists made a new definition of a planet. According to IAU (International Astronomical Union), a planet is a celestial body that: –
1: is in the orbit around the Sun
2: has enough gravity to pull itself into a sphere
3: has cleared the neighborhood around its orbit.
The above definition is given by IAU, do you have your own definition of a planet?
Sadly, Pluto fails the Third criteria. Therefore, Pluto was termed as a dwarf planet.
According to IAU, there are 8 planets, 5 dwarf planets, 181 moons, 566,000 asteroids, and 3100 comets.
Pluto isn’t the only dwarf planet in the solar system, here are all the dwarf planets: –
The Pluto was discovered by Clyde Tombaugh in 1930 and is one of the members of the Kuiper belt. Pluto is the founding member of the dwarf family. It takes Pluto 248 years to make an orbit around the Sun, and out of that only 20 years are spent inside Neptune’s orbit.
Pluto was demoted as a planet in 2006. Pluto has five moons: Charon, Nix, Kerberos, Hydra, and Styx.
Ceres has a diameter of only 1000km, therefore, it is the smallest dwarf planet. Giuseppe Piazzi discovered Ceres in 1801. It contains 30% of the combined mass of the asteroid belt. Ceres surface is made of ice and rock.
Haumea was discovered in 2003 and its moons in 2005. It is egg-shaped and has two moons: Hi’iaka and Nakama. The planet orbits the Sun once every 285 years. Haumea is a third of the mass of Pluto.
Makemake is also located in the Kuiper belt. It was discovered in 2005 and is two-thirds the size of Pluto. Makemake orbits Sun once every 310 years.
Eris is 27% more massive than Pluto. It also has one moon called Dysnomia. Eris orbits Sun once every 557 years.
Mercury is the closest planet to the Sun and is the smallest planet in the solar system. Mercury has no natural satellites. The planet Mercury has a very thin atmosphere.
Mercury is visible from the naked eye. Closer the planet is to the Sun faster it moves in order to stay in the orbit therefor Mercury is the fastest planet in the solar system.
Diameter: 4878 km
Orbit: 88 Earth Days
Day: 58 Earth Days
Venus is called the morning star or evening star because it is always close to the sun during sunrise or sunset. It is close to the size of the earth.
Out of all planets in the solar system, Venus is the hottest. It has a very dense atmosphere. Carbon dioxide is the main component of the Venusian atmosphere.
Venus spins the opposite compared to other planets. It has no magnetic field. Venus doesn’t have any natural satellite.
Orbit: 225 Earth Days
Day: 241 Earth Days
Earth is the only planet in the solar system where life is known to exist and where we live. Water covers 2/3 of the Earth’s surface
Earth has a small ozone layer which is a layer made up of O3 gas which reflects the Sun’s UV radiation. As we all know that our planet has one satellite (Moon). Earth is the densest planet in the solar system.
Orbit: 365.2 days
Day: 24 hours
Mars is often called the red planet because its surface is made of high ironic content. It is smaller than Earth and Venus. Mars’s atmosphere is mostly made of Carbon Dioxide. It has rocky mountains and valleys just like earth.
Mars has the highest volcano in the solar system Olympus Mons, which is 20km high. The planet has two natural satellites Delmos and Phobos thought to be either asteroid or ejected from massive impact in the early days.
Orbit: 687 Earth days
Day: 24.7 hours
The planet Jupiter is by far the biggest planet in our solar system. Its mass is 2.5 times greater than the mass of all the planets combined. It is so big that 1300 piles of earth can fit in it. Planet’s atmosphere is mostly made up of Hydrogen and Helium.
The planet also has the Great Red Spot where four piles of earth can easily fit in. It has 79 satellites of which Ganymede is the largest and also the largest in the solar system. And, Hey! It rains diamonds on the mighty gas giant.
Diameter: 142,984 km
Orbit: 4331 Earth days
Day: 9.9 hours
Saturn is arguably the most beautiful planet in the solar system. It is mostly known for its rings. Saturn is less dense than water. Saturn has 59 named satellites of which Titan is the biggest, it is bigger than Mercury.
Diameter: 120,536 km
Orbit:10,747 Earth days
Day: 10.7 hours
Firstly, Uranus orbits the sun on its sides. The atmosphere is composed mainly of Hydrogen and Helium.
The planet has a blue-green color because of Methane in its atmosphere. Uranus has 11 inner rings and 2 outer rings. Uranus has 27 known moons.
Diameter: 51,118 km
Orbit: 30,589 Earth days
Day: 17.2 hours
Like Jupiter Neptune also has a great dark spot which is larger than Earth. Neptune has six known rings but they are relatively short-lived. Neptune has 14 satellites.
Diameter: 49,528 km
Orbit: 59,800 Earth days
Day: 16.1 hours
Did You Know? Scientists are speculating the potential existence of the actual Ninth planet (not Pluto) which is predicted to be 10 times the size of planet earth.
At the beginning of the 21st century, there was a lot of speculation about this topic. In 2006 IAU finally settled the debate. Maybe a little harsh on Pluto.
Do you think that the definition of a planet should be redefined again? What do you think of the new planet nine speculations?
Prajyot KumbharjuvekarCo-founder of astronomiac
Prajyot is a writer and co-founder of Astronomiac. Writer at day and reader at night, he writes everything about astronomy.
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- Planet Venus: The Ultimate Guide
- Planet Earth explained in just 2639 words
- Planet Neptune, everything you want to know
- Jupiter: The solar system giant