Today’s Wonder of the Day was inspired by Jacob from Vancouver. Jacob Wonders, “What is a Rogue Planet?” Thanks for WONDERing with us, Jacob!

Have you ever stared up at the night sky and thought about all the heavenly objects out there? Maybe you’ve watched a comet fly past or a shower of meteors fall toward the Earth. Or perhaps you just gaze up at the stars, imagining all the other planets orbiting each one.

Did you know not all planets orbit a star? It’s true! Some planets travel through space on their own, floating in whichever direction gravity pulls them. We call these untethered flying objects rogue planets.

How many rogue planets are there? No one is quite sure. However, experts say there may be billions in the Milky Way galaxy alone. In fact, they now believe there could be more rogue planets in our galaxy than there are stars. 

Because rogue planets are in constant motion and do not give off light, they’re difficult to detect. However, NASA now hopes to find these roaming nomads with a new device. It’s called the Nancy Grace Roman Space Telescope. 

This telescope will help scientists find rogue planets by detecting microlensing. That’s when light from a star bends toward a planet’s gravity. By sensing this bending of light, the Roman Space Telescope will be able to help scientists find rogue planets that were once undetectable.

How does a rogue planet become . . . well, rogue? Does it just decide to set off on its own one day? Wave goodbye to its star and set out into the great unknown? No, of course not! Instead, many are forced out of their solar system by the gravity of another planet or star. They may also simply form on their own, separate from any star.

What would it be like to stand on the surface of a rogue planet? The conditions on these celestial objects are still largely a mystery. However, experts agree that they’re much different from Earth—or any other planet with a normal orbit, for that matter. Since rogue planets don’t move around a star, they have no daylight. Instead, they exist in constant night. That means they also have little warmth and are icy worlds.

Upon learning about rogue planets, many people ask the same question: Is there one in our solar system? Experts don’t think it likely. While rogue planets are hard to detect, we would have noticed one so close to Earth by now. Its gravity would have an effect on our orbit, heavily impacting life on this planet. Though there may be billions of rogue planets in our galaxy, experts don’t think we have to worry about one entering our solar system anytime soon. 

What do experts hope to learn from studying rogue planets? These solitary travelers could teach us a lot about how planets form and evolve. They’ve already found one rogue planet that’s about 12 times the size of Jupiter! Another—the closest to us, in fact—is about the size of Mars. The knowledge scientists could gain from studying these other worlds could become very important to the future of our planet.

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Wonder What's Next?

Learn about the oldest major religion in tomorrow’s Wonder of the Day!