Name: The REAL Reason Asteroids Aren't Planets
Uploaded: 2026-01-23T18:27:37.000Z
Duration: 4 min 23 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

When the first asteroids were discovered over 200 years ago.

And the story goes that the rapid and overwhelming discovery of hundreds.

Quickly convinced scientists that asteroids shouldn't be planets.

The real reason asteroids were demoted from planet status.

Came nearly a hundred years after the hundredth asteroid was discovered.

And had nothing to do with their quantity, but in fact, their quality.

Of course, up until 1800, only seven primary planets.

Only seven primary planets had been Mercury, Venus, Earth, Mars, Jupiter, Saturn, and Uranus.

But telescopes got better, and we found more.

A small eighth primary planet, Ceres, was discovered in 1801 between Jupiter and Mars.

And then there was a surge of new planets.

Discovered with almost identical orbits to Ceres, Pallas, Juno, Vesta.

And more and more and more, it soon became clear that there was a band of small planets.

Orbiting the sun between Mars and Jupiter.

And so, when describing the solar system, Astronomers found it useful to group them together as the small planets, the minor planets, the planetoids, the asteroids, or the numbered planets.

Because eventually, so many were being discovered so quickly.

It was easier to keep track of them all with numbers.

But there wasn't yet any scientific reason to stop thinking of the asteroids as planets.

I mean, having too many isn't by itself a good scientific criteria.

Think of all the thousands of known planets we've now discovered orbiting other stars.

Their sheer number isn't a reason not to call them planets or the elements.

Doesn't mean we should stop calling them elements.

So despite some embarrassment over the rapidly growing list of planets.

19th and early 20th century astronomers still considered all the asteroids to be planets.

Well, except one astronomer who argued that the asteroids should be their own category.

But his reasoning was based on incorrect data and theoretical misunderstandings.

And was ultimately rejected by the wider astronomical community.

Even today, the International Astronomical Union's commission on asteroids.

Is still technically named the Minor Planet Center.

Even though, as we're about to discover, it's a poor name for them.

So why don't we include the asteroids in our list of planets today?

Look at this analysis of scientific papers in the last 200 years.

The terms small planet and minor planet had consistent use relative to asteroid.

Right up until 1953, when, boom, their use plummeted.

This change wasn't because of a fear of a huge list of planets.

Asteroids, it turns out, Are not just miniature versions of the larger planets, but

are in fact, fragments from the collisions and disintegration of other planets.

This distinction matters because when planets form, the release of gravitational potential energy Partially melts their interiors, Causing heavy elements to sink to the core and lighter materials to float upwards, Sorting into layers.

If asteroids were formed like planets, but

smaller, they would each be made of a mix of materials and would be too small to have enough energy to sort the materials into layers.

If instead, asteroids were relics from collisions between planets, each one would be a mostly homogenous chunk of material From a single layer.

And what astronomers figured out Was that asteroids Are definitely broken planet pieces.

In fact, asteroids are literally classified into groups Based on what materials they're made of.

Out of the ridiculous number of objects in the asteroid belt, There are only three or four that we think formed on their own as a planet.

Rather than being broken fragments, these three or four are the Ceres, Vesta, Pallas, and maybe Hygiea.

So the asteroids were demoted to non planet status, not by a vote, Nor from a fear of long lists of planets, Due to a scientific discovery that asteroids are, in fact, Physically different From everything else that we call planets.

The discovery meant they were split off in the minds of scientists into their own group, and

those scientists organically Stopped calling them planets.

In principle, the taxonomic split could have gone the other way.

Researchers could have kept calling asteroids planets and come up with a new name for the remaining non fragmented objects like the earth.

But given the fact that asteroids were already previously considered A subcategory of planet minor planets, it makes much more taxonomic sense to split them off and keep all the rest of the planets as planets.

By this logic, we should probably also stop calling Ceres, Vesta, and

Pallas astero since they formed like planets do.

So even though there are lots of asteroids.

For the question of whether or not asteroids count as planets, it turns out that quality matters more than quantity.

Seeing the innumerable fascinating but completely inhospitable worlds in our solar system Is a reminder of just how diverse, unique, and

But to keep planet Earth as our home, we have to look after it.

That's why we're working with the nature protection community, Called Planet Wild, Our sponsor for this video.

Every month, the Planet Wild community funds a mission to restore the oceans, forests, and

All of this is documented through videos here on YouTube.

Just like this mission restoring lost peatland ecosystems, you can join in supporting solution oriented missions globally by giving whatever amount you want the first 100 people to sign up using our code, MinutePhysics1 will get their first month covered.

Just scan this QR code or click the link in the description.

Subtitles ListPlay Video

The REAL Reason Asteroids Aren't Planets

sort

ridiculous

overwhelming

delicate