Look up on a clear night and a bright light may seem to hover. Someone may report it. The word for what they saw is UFO, which stands for unidentified flying object. That means something in the sky that the person who saw it could not identify at that moment. The word names a puzzle. It does not name a spaceship.

Some of the answers are ordinary things. Bright planets such as Venus and Jupiter, and meteors, are sometimes reported as strange lights because they can look like they are hovering or moving. Weather and research balloons are sometimes reported too. High-altitude balloons often lack markings and can look strange from certain angles.

Ordinary aircraft are a common cause of UFO reports. Seen from odd angles or in poor light, they can look unusual. In the 1950s and 1960s, secret high-flying planes caused many reports. People saw an aircraft that they could not name.

You may have heard that a UFO is an alien spaceship. In fact, unidentified means the person could not identify the object at that moment. It does not say what the object was, and it does not say it came from another world. Planets, meteors, balloons and aircraft are all sometimes reported, and a report is a question to check, not a conclusion.

The other half of the search looks at planets, with measurements instead of sightings. A planet that goes around a star other than our Sun is called an exoplanet. Scientists use telescopes, some of them out in space, to look for planets around other stars. As of November 2026, more than 6,000 are confirmed.

Scientists can watch a star, so a planet can show itself through the star's light. One way to find a planet is to watch the star for tiny dips in its light when a planet passes in front of it. This is called a transit. Another way is to watch for a star that wobbles: the gravity of an orbiting planet tugs the star back and forth.

Finding a planet is not the same as finding life. The habitable zone is the area around a star where a planet could have liquid water on its surface: not too hot and not too cold. A planet in that zone could have liquid water.

Closer to home, Mars is a small, rocky planet, about half the size of Earth. It is red because of rusty iron in its ground, and it is a cold desert world. Long ago, it had rivers and lakes: it has ancient river valleys, deltas and lakebeds, so water most likely once flowed there.

Rovers are robots with wheels that drive around Mars, taking pictures and measurements. As of November 2026, some of them look for signs that tiny living things could have lived on Mars long ago. A sign is a hint, and a hint is not the same as an answer.

So where does the evidence stand? As of November 2026, scientists have not found life anywhere beyond Earth, and the search goes on.

Words to know

• unidentified: not yet known
• transit: planet crossing
• habitable: fit to live
• exoplanet: far-off planet
• meteors: shooting stars