planets and solar system facts

We’ve obviously learned a lot since the days of ancient Greek, Babylonian, and Chinese astronomy, which only inspires modern astronomers to learn even more about our home among the stars.

What is the solar system?

The solar system is a region of space, and all objects within it are gravitationally bound to the sun.

That means every planet and moon, every asteroid and comet, and every bit of space dust in between.

It formed around 4.6 billion years ago from a massive pocket of gas, dust and other debris known as a molecular cloud in a way that is still the subject of of debates.

Something, possibly a supernova, disturbed the cloud enough for a density imbalance to form, which then created a center of gravity strong enough for it to accumulate more cloud within itself, eventually forming the sun.

The sun is estimated to contain about 99% of the material in this original molecular cloud, with the remaining 1% representing all the planets, asteroids and everything in between.

How many planets are there in the solar system?

The eight planets of the solar system. Pluto is not one of them. | Source: NASA

Currently, there are officially eight planets in the solar system, with an unknown number of dwarf planets contained almost exclusively within an outer belt of rocky material known as the Kuiper Belt.

The planets, in order of distance from the sun, are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

A planet is defined as a massive body that has a regular primary orbit around the sun, has gravity strong enough to overcome rigid body forces to transform into a spheroid shape, and (most importantly) must have cleared the neighborhood around its orbit .

Dwarf planets are bodies that possess the first two of the three required characteristics but have not yet cleared their orbits of matter.

What happened to Pluto?

Our solar system is rocking: here's everything you need to know about it
Pluto, seen by the New Horizons probe in 2016. | Source: NASA/JPL-Caltech

When discovered in 1930, Pluto was considered the ninth planet in our solar system, a status it held until 2006, when it was reclassified as a dwarf planet.

Many people who grew up learning that Pluto was a planet clung to the idea over the next nearly two decades, making Pluto’s status as a planet something of a cultural touchstone for many. people.

But once you understand the reasoning behind the demotion, it makes a lot of sense.

How many dwarf planets are there in the solar system?

There are currently six recognized dwarf planets: Pluto, Ceres, Eris, Makemake, Haumea and 2015 RR245 (which does not yet have an official “name”, as of 2022).

If we were only talking about six more dwarf planets in the solar system, you could argue that there really were 14 planets in total, rather than eight, but the six known dwarf planets aren’t the only ones, by far.

We know of over 20 dwarf planet candidates and there are probably many more that we haven’t spotted yet, which makes dwarf planets much more common than traditional planets, and also something quite different from planets as we know them.

Arline J. Mercier