Which statement about exoplanets is true?

Question

They only appear once before they disappear in space.
They can be detected by ordinary telescopes.
They are objects that are no longer considered planets.
They are discovered when they dim a star they pass by.

Answer 1

The true statement about exoplanets is: They are discovered when they dim a star they pass by.

This method of detection is known as the transit method, where astronomers observe a slight dimming of a star's light when a planet transits, or passes in front of it, from our perspective on Earth.