exomoon
Exomoons are natural satellites of exoplanets. Their detection is the cutting edge of observational astronomy. Two main methods are used for the search. During the transit of a planet across the star's disk, a moon can cause an additional slight dimming (photometric method). Additionally, the moon's gravity makes the planet wobble, which leads to uneven timing of transits—transit timing variations (TTV). Detection requires ultra-precise measurements, so the main hopes are pinned on telescopes like Kepler, TESS, and future missions. It is thought that exomoons can be born from a circumplanetary disk or be captured by the planet's gravity. Their presence expands the possible habitable zones, as a moon can maintain a stable climate thanks to tidal heating and the presence of an atmosphere.
History
The idea of moons around exoplanets arose simultaneously with the idea of exoplanets themselves. The first serious attempts to detect an exomoon began in the 2000s with the launch of the Kepler telescope. There is no universally recognized discovery yet, but there are several candidates requiring confirmation.
How it works
When a planet with a moon passes in front of a star, the moon adds a small dip to the light curve. The effect is barely perceptible, like the shadow of a small bird against the Sun, but precise instruments can detect it. In addition, the moon's gravity causes the planet to wobble, causing the transit timings to shift slightly.
💡 The most famous candidate is the moon of the planet Kepler-1625 b, which could be the size of Neptune. If its existence is confirmed, it will be the first discovered 'mega-moon'.