A rainbow on the Martian sky taken by the Mars rover Perseverance made the headline recently. NASA people explained that a natural rainbow is impossible on Mars because the Martian atmosphere is too dry and too cold for sufficient water droplets to stay. The "Martian rainbow" is actually a "lens flare" image artifact. There are more examples from the photos of the Apollo Moon landing missions.

Lens flare may be noticeable when there is stray light from strong light for example sunlight near the camera, that undergoes internal reflections inside the camera lens. Depending on the light source's position and the lens design, lens flares can show up as hazes, polygons or arcs in rainbow colors.

You think NASA's explanation is questionable? Flick your camera against light sources to create your original lens flares.