Last Friday, a mysterious object flying above Earth appeared on the International Space Station’s live stream moments after it went dead. Naturally, some conspiracy theorists claimed this was a UFO being flown around by intelligent extraterrestrial visitors.

The chances of that being the case are almost close to zero. These “sightings” on NASA’s ISS live stream happen all the time, and there are always explanations that don’t lead to UFOs and aliens.

According to former NASA engineer James Oberg, if anything unusual appears in front of a camera, it’s likely coming from inside the spacecraft. On Earth, we’re used to seeing things from the point of view of standing still. But objects in Earth’s orbit are traveling fast — the ISS itself is zipping through space at over 17,000 mph. If a UFO really appeared, it would only be visible for a short moment.

One explanation is that this shape is a reflection from the station windows or lights from Earth. This could also be a lens reflection that changes as the light changes, creating the perception of a UFO coming into view and then flying away. These reflections can then appear on photos and videos from space.

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These “UFOs” could also actually be “space dandruff.” This stuff doesn’t come from your scalp when it’s dry, but from ice flakes, insulation fragment,s or fragments from the shuttle that may look like UFOs in the sunlight.

“Twilight shadowing” can also cause saucer-like optical tricks. When you see objects that suddenly appear or disappear on screen, usually they’re just moving in and out of the spacecraft’s shadow.

On Earth, shadows are cast on the ground, wall, or any surface nearby. These types of surfaces aren’t found in space, so a spacecraft’s shadow is invisible. When space dandruff flies nearby, the speeding spacecraft casts a shadow. Hence, a mysterious shape flits in and out of the camera’s view.

Although interest in UFOs among scientists was quelled a long time ago, public fascination remains as high as ever. UFO research teams still exist today, and conspiracy theories about NASA covering up UFO sightings spring up pretty frequently, even when they’re debunked by science. The truth is out there — even if it’s just dandruff.

Photos via International Space Station