There's no gravity in space

If this myth were true, the universe would be a far different place.

By Michael E. Bakich

Gemini 4 astronaut Ed White conducts a spacewalk June 3, 1965

During the Gemini 4 mission, astronaut Ed White conducted a spacewalk June 3, 1965. Although he appears weightless, gravity from Earth, the Moon, the Sun, and elsewhere acts upon him when he’s in space.

Photo by NASA

This is false, but it's easy to understand how this myth got started. Pictures and movies of astronauts orbiting Earth or on their way to the Moon show them floating in their spacecraft. Likewise, images capture shuttle astronauts who conducted spacewalks to repair the Hubble Space Telescope drifting tethered beside the main body of the spacecraft. And, early in the manned space program, pilots and some scientists incorrectly began referring to space as a place of "zero gravity."

Gravity is a force created by any body that has mass. We usually think of the Sun, Moon, and planets (especially Earth) as objects that have gravity, but you and I, because we have some mass, also exert a gravitational force — albeit a really tiny one!

Without getting into some heavy-duty equations here, British mathematician Isaac Newton (1643-1727) proved that gravitational force decreases as the distance from any object increases. But it never vanishes. In fact, Earth's gravity 62.5 miles (100 km) above its surface is still 97 percent as strong as its gravitational pull at sea level.

So, for example, the Sun's gravitational attraction of Mercury (the closest planet) is stronger than its gravitational attraction for Venus, Earth, or any other planet. (That's why Mercury has to move faster than the other planets. If it orbited at the same speed as Earth, the Sun quickly would swallow it.) Likewise, Earth's gravity keeps the Moon circling around us once every 27.3 days, and Jupiter's gravity keeps more than 60 moons orbiting around it.

So, if there's gravity in space, why does it look like the astronauts are floating? The reason is that objects in space are in a continuous state of freefall. This term describes a state of motion with no acceleration other than that provided by gravity. A similar thing could happen on Earth to an elevator passenger and her purse, both of which would be equally "weightless" if the elevator fell rapidly enough.

And consider one last fact. If there were no gravity in space, weather and communication satellites would not orbit Earth, Earth would not orbit the Sun, and the Sun would not orbit the center of the Milky Way. Indeed, everything would shoot off in a straight line, and chaos would rule. But there is gravity in space, and lots of it.

Learn more about astronomy with these resources

Know the facts — not the fiction — about astronomy and sign up for Astronomy magazine's free weekly e-mail newsletter.
See stunning images of comets, galaxies, nebulae, and more in our Online Reader Gallery.
Read the latest astronomy news.
Go behind the scenes of the hobby, science, and magazine in our editors blog.