{"id":53417,"date":"2024-01-11T09:01:37","date_gmt":"2024-01-11T09:01:37","guid":{"rendered":"http:\/\/3a4a9eff-1164-410d-99c9-72428e8902da"},"modified":"2024-01-11T11:32:33","modified_gmt":"2024-01-11T11:32:33","slug":"how-many-planets-are-there","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/how-many-planets-are-there\/","title":{"rendered":"How many planets are there?"},"content":{"rendered":"

What makes a planet? How many are there in our Solar System and the wider Universe? <\/p>

By Russell Deeks\n <\/p>

Published: Thursday, 11 January 2024 at 09:01 AM<\/p>

\n\n

How many planets are there? There are 8 planets in our Solar System, of course!<\/p>

But this is a trickier question to answer than you might think, at least historically speaking.<\/p>

The answer to how many planets there are used to be simple, as those of us who are old enough will recall.<\/p>

There were nine planets, they all orbited the Sun and, following a poll of astronauts and cosmonauts, Earth was officially declared the happiest of them.<\/p>

Are you a teacher? Demonstrate the order of planets with our DIY project to make a scale model of the Solar System<\/a><\/em><\/strong><\/p>

Illustration of the planets of the Solar System. Credit: Steve Allen \/ Getty Images<\/figcaption><\/figure>

Which was good, because by some remarkable coincidence, \u201cSpace men vote Earth most jolly of solar universe\u2019s nine planets\u201d just happened to start with all the same letters as the order of the bodies of the Solar System: Sun, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.<\/p>

Funny, that!<\/p>

Only then things changed.<\/p>

The loss of Pluto the planet<\/strong><\/h2>
\"The
The discovery of large objects in the Kuiper Belt led to a re-think as to how many bodies in our Solar System we classify as planets.<\/figcaption><\/figure>

In the late 1980s and early 1990s, astronomers began to find other large objects lurking out beyond Neptune, known as Trans-Neptunian Objects (TNOs).<\/p>

These large objects populate the Kuiper Belt<\/a> on the edge of the Solar System.<\/p>

This culminated in the 2005 discovery of Eris, roughly the same size as Pluto but with 27% more mass, strengthening the argument that Pluto shouldn’t be considered a planet.<\/p>

Meanwhile, other astronomers had by 1992 positively identified the first exoplanet<\/a> \u2013 that is, a planet outside our own Solar System.<\/p>

As time went on, it became clear that far from being unique to the neighbourhood surrounding the Sun, planets were almost certainly abundant throughout the Universe.<\/p>

In fact, many astronomers now believe that, wherever you see a star, you\u2019ll find at least one planet \u2013 if not an entire planetary system akin to our own.<\/p>

\"There
There are now thought to be more planets than stars in the sky. Credit: John White Photos \/ Getty Images<\/figcaption><\/figure>

What makes a planet<\/strong><\/h2>

Faced with a sudden abundance of ‘planets’ both on our doorstep and further afield, the International Astronomy Union decided in 2006 that a new, stricter definition of the word was required.<\/p>

They came up with three criteria for Solar System planethood:<\/p>