Why don't planets fall into the Sun?

They are falling toward it, but they also move sideways at high speed. That sideways motion carries them past the Sun again and again, so their path curves around it instead of ending in a collision. The balance has held for billions of years.

Do all planets orbit the Sun in the same direction?

Yes, all eight planets travel around the Sun in the same direction, in nearly the same flat plane. This is best explained by their shared origin in one spinning disk of gas and dust, though some details of the early solar system are still studied.

Does the Sun orbit anything?

Yes. The Sun orbits the center of the Milky Way galaxy, and one trip takes roughly 225 to 250 million years. The Sun also wobbles slightly because its planets tug on it, so they really orbit a shared center of mass close to the Sun.

Who figured out how planets orbit?

Johannes Kepler described the shapes and timing of planetary orbits from careful observations, showing they are ellipses. Isaac Newton then showed that gravity explains them. Later, Albert Einstein's general relativity refined the picture, for example in the orbit of Mercury.

Topics Space and the universe

Why do planets orbit the Sun?

Planets orbit the Sun because the Sun's gravity keeps pulling them inward while their sideways speed keeps carrying them forward. Neither wins. A planet is always falling toward the Sun, but it is also moving so fast across the Sun's path that it keeps missing. The result is a curved, looping path we call an orbit.

The more interesting question is why planets were moving sideways to begin with. The best-supported answer is that the Sun and planets formed together, about four and a half billion years ago, from a spinning cloud of gas and dust. As the cloud collapsed, it flattened into a disk and kept its spin. The Sun formed in the middle, and the planets built up from material still circling in the disk. Details of how planets grew are still debated, and astronomers keep revising them.

An episode on this would start with a ball thrown off a tall tower, then work up to the whole solar system. It would also be honest about what we do not fully know. bre's hosts are AI, so they can make mistakes, and you can press Talk to ask a question mid-episode.

What a bre episode would cover

An outline of the episode bre would make for this question. Every episode is written fresh when you ask, so yours will differ.

Falling and missingAn orbit is a fall that never lands. A planet is pulled toward the Sun, but its sideways motion means it keeps missing, so its path curves around the Sun.
Gravity: the pull from the SunThe Sun holds nearly all the mass in the solar system, so its gravity dominates. Planets farther out move more slowly, which follows from the weaker pull at greater distance.
Where the sideways motion came fromThe solar system formed from a collapsing, spinning cloud of gas and dust. The spin was never lost, it just got concentrated into a flat disk.
Why the orbits are nearly flatPlanets circle in roughly the same plane and the same direction because they formed from the same spinning disk. That picture is well supported, though not every detail is settled.
Ovals, not perfect circlesOrbits are ellipses, as Johannes Kepler worked out from observations. Some are almost circular, others are noticeably stretched.
Does anything ever escape?A fast enough object can leave the Sun's pull, and a slow one can fall in. Planets sit in a stable balance, though over very long times small tugs between them add up.

How the episode might open

A sample exchange between two of bre’s AI hosts, bre and Arlo. Both are AI; this is written by AI, as every bre episode is.

breAI host
Here's the picture I want to start with. You're on a tall tower and you throw a ball. It drops to the ground. Throw it harder, it lands farther away. Now keep going.
ArloAI host
It lands in another country.
breAI host
Then keep going until the ground curves away beneath it as fast as the ball falls. It never lands. That's an orbit.
ArloAI host
So Earth is falling.
breAI host
All the time, toward the Sun. But Earth is also moving sideways so fast that its path curves around the Sun as it falls, and it keeps missing.
ArloAI host
Why sideways? Who started that?
breAI host
Good question, and the answer is the solar system's birth. A giant spinning cloud of gas and dust collapsed, and the spin stayed. Planets inherited it.
ArloAI host
Who counted that?
breAI host
Nobody watched it. Astronomers piece it together from our own planets and from young stars with disks. Some details are still debated.

Questions people also ask

Why don't planets fall into the Sun?: They are falling toward it, but they also move sideways at high speed. That sideways motion carries them past the Sun again and again, so their path curves around it instead of ending in a collision. The balance has held for billions of years.
Do all planets orbit the Sun in the same direction?: Yes, all eight planets travel around the Sun in the same direction, in nearly the same flat plane. This is best explained by their shared origin in one spinning disk of gas and dust, though some details of the early solar system are still studied.
Does the Sun orbit anything?: Yes. The Sun orbits the center of the Milky Way galaxy, and one trip takes roughly 225 to 250 million years. The Sun also wobbles slightly because its planets tug on it, so they really orbit a shared center of mass close to the Sun.
Who figured out how planets orbit?: Johannes Kepler described the shapes and timing of planetary orbits from careful observations, showing they are ellipses. Isaac Newton then showed that gravity explains them. Later, Albert Einstein's general relativity refined the picture, for example in the orbit of Mercury.

Why do planets orbit the Sun?

What a bre episode would cover

How the episode might open

Questions people also ask

Related topics