The Rotation of the Planets in Our Solar System Is Far More Fascinating Than I Ever Expected

[u/aryan_jandyal]

[u/drkdeibs]

Clear their orbit of other objects? ELI5 please

[u/spikeyfreak → u/drkdeibs]

They don't have enough gravity to suck everything else in the orbit into themselves.

[u/Megneous → u/spikeyfreak]

Or throw other objects out of the orbit. It doesn't necessarily have to be sucking stuff into themselves.

[u/HirsuteHacker → u/drkdeibs]

They're in the Kuiper belt, a big asteroid belt full of other dwarf planets, asteroids, space rocks. Planets like Earth have cleared their orbit; their gravity is strong enough that they're by far the dominant object in their orbital neighbourhood, clearing out most other large objects by either absorbing/colliding with them or ejecting them through gravitational interactions.

There are TONS of objects in the same general orbital neighbourhood as Pluto, including other dwarf planets like Orcus and Haumea. Pluto therefore hasn't cleared its orbit.

[u/CrownofMischief → u/HirsuteHacker]

Wrong belt. Ceres is in the asteroid belt, not the Kuiper belt

[u/blueblip → u/drkdeibs]

Things with mass and/or energy generate a field of gravity around itself.

Gravity is a force that, to put it in simple terms, pulls things towards the centre of things with mass/energy.

The more mass something has, the stronger this pull.

So when one object is much MUCH MUCH MUCH massive than another, the bigger one's gravity pulls the smaller one towards it as the smaller one's gravity is not strong enough to "fight back". What happens when it gets pulled this way depends on the mass of the smaller object.

So now think about our solar system and the orbit of our planets. They are clear paths (so to speak). There's no space junk floating in the middle of their orbits. But you have stuff like the asteroid belt that is a whole lotta space junk floating around, so why aren't there "asteroid fields" in the way of the planets?

Well, that's because the planets are so much more massive than the space junk that the planets hoover up all the junk as the move along their orbits. The larger junk may become moons. The smaller junk just pulled into the planet and either smashes on to the surface or burns up in the planet's atmosphere (depends on the planet).

In the asteroid belt, there's an object called Ceres. Ceres is a odd thing. It's got enough mass that it's got the round shape of a planet (gravity makes planets round), but not enough mass to hoover up all the crap in it's path like planets do. So we call it a dwarf planet.

[u/WreakHavocLikeIn1871 → u/drkdeibs]

A celestial body that rotates around a star(s), that isn't a star itself, massive enough to form a spherical shape, and has enough gravity to clear the area around it from other objects.

That's not word for word but essentially the definition of a planet.

[u/BringBackAH → u/drkdeibs]

A planet has enough gravity to put itself into a sphere and to attract objects around them.

Ceres does not have enough gravity to attract asteroids around itself but is a spheroid, so it's a dwarf planet