Why Do Planets Orbit the Sun?

We often take for granted our unique position in the universe, voyaging incessantly around our star with seven planetary neighbors and countless pieces of space debris. We don’t even notice as we fly through space, so why do planets orbit the Sun at all?

This diagram illustrates the positions of Mars, Earth and the sun during a period that occurs approximately every 26 months,

The Origin of the Solar System

Some 4.5 billion years ago, the Solar System began from a cloud of gas and dust. Possibly due to a nearby supernova explosion, the cloud collapsed in on itself. This collapse formed a solar nebula, a disc of cosmic material.

Over time, this disc began to form into the objects we recognize today. The intense gravity at the center of the disc pulled in most of the material, creating our Sun. The leftover 1% of matter coalesced into the planets, moons, asteroids, comets, and meteoroids.

Planets and Inertia

Something, presumably that nearby supernova, started the matter in the solar nebula moving through space. According to Isaac Newton’s first law of motion, this material pushed by the external force of a supernova should have sent it in a straight line indefinitely. 

Since there is no friction in space, there’s no opposing force to slow down or stop these planets from continuing in that same direction through space.

The Power of the Sun’s Gravity

It should come as no surprise that the planets, asteroids, and comets didn’t continue on a straight line into space. Instead, another force acted upon these objects to pull them into an orbit. That force? The gravitational pull of our fledgling Sun.

X-rays stream off the sun in this picture of the sun
X-rays stream off the sun. (Image credit: NASA)

As the Sun pulled in nearly 99% of the available gas and dust in the Solar System to form into a star, it also tugged at the larger rock and gas formations that were taking shape. These objects had already accumulated too much mass and too much speed to be pulled into the Sun.

However, the Sun’s gravity was strong enough to save each of our planets from sailing out of the Solar System. Each of the eight planets and millions of asteroids settled into a specific orbit resulting from their initial momentum and the Sun’s pull.

Orbits Are Elliptical

It would make sense to think that a planet’s orbit makes a perfect circle around the Sun, but this isn’t quite the case. Each world follows an elliptical or oval-shaped path as it travels around the Sun. The Earth only has an eccentricity of 1.7%, which wouldn’t even be discernible if seen with the naked eye.

The gas giants average 4% eccentricity in their orbits, whereas Mercury has the most elliptical orbit at 20%. Before it was declassified, Pluto had the award at 24.4%.

The Solar System Is One Flat Plane

This artist's diagram depicts our solar system's eight planets.

As mentioned earlier, the cloud of dust that the Solar System formed from was compressed into a thin, flat disc. Even today, 4.5 billion years later, the Solar System still exists in that same plane. Each of the planets, Sun, and Moon follow the same imaginary line through the sky called the ecliptic.

The same external force that condensed our cloud started the disc spinning. Everything still moves in the same counterclockwise direction today.


Why Do We Not Feel the Earth Moving?

The Earth moves at a brisk pace as it travels around the Sun. We’re talking approximately 67,000 miles per hour (107,800 kilometers per second) every moment of every day. Why don’t we feel the wind in our hair as we fly through space with it?

The answer comes down to two similar but very different terms – velocity and acceleration.

If you’ve ever been on an airplane, you can certainly feel the force when it picks up speed down the runway. The same holds true if you’re speeding up in a car on the road. However, once you’re at a steady velocity, you no longer feel the motion because your speed is constant.

This holds true for the Earth as well since we’ve been moving at a steady speed since time immemorial. Should the Earth suddenly speed up or slow down, we would feel that for sure.

What Happens if the Earth Falls Out of Orbit?

The sun shines above the Earth's horizon as the International Space Station
The sun shines above the Earth’s horizon as the International Space Station.

A change in the Earth’s velocity as it travels around the Sun could significantly impact life planetside.

It’s worth noting that it would take an external force of some kind, such as a collision or the force from a massive cosmic explosion, to cause such a change. As nearly impossible as that is, such an event could speed up or slow down our planet.

If the Earth Slowed Down

If the Earth slowed down, the Sun’s gravity would pull us ever closer to it. Even a minor change can have a considerable impact on our climate, with temperatures reaching all-time highs. If we were ever to reach Venus’s orbit, temperatures would be too hot for all but the most heat-resistant bacteria to survive.

Most likely, the Earth would eventually plunge into the Sun, which is bad news for everyone on board.

If the Earth Sped Up

If the Earth were to increase its speed, the opposite effect would take place. We’d move away from the Sun and settle into a new orbit closer to Mars, where things would be colder than they are today.

In a worst-case scenario, the Earth could break free of the Sun’s gravitational hold and float endlessly into the cold recesses of space. For that to happen, the Earth would have to travel 26,700 miles per hour (43,400 kilometers per hour) faster than it does today.

Let’s find out how the humanity can save itself in the face of this situation.

Final Thoughts

The Sun, planets, and everything else in the Solar System formed from the same cloud of gas and dust some 4.5 billion years ago. Because of this, we see similarities throughout the Solar System in the direction and plane we all revolve in. Thankfully, the Earth is situated perfectly between our velocity and the Sun’s gravity to sustain life on the surface.

About Noah Zelvis

Noah is a content writer who has had a love of all things astronomy for as long as he can remember.
When not reaching for the stars, you’ll likely find Noah traveling or running.