A team of astronomers is on a search for moons, particularly the size of Earth moon, around extrasolar planets using available Kepler data.

Exomoons, or extrasolar moon, is a natural satellite that orbits an extrasolar planet or other extrasolar body. Although no extrasolar moons have yet been observed, it can be inferred from the empirical study of natural satellites in the Solar System that they are likely to be common elements of planetary systems.

The team, led by David Kipping from the Harvard-Smithsonian Center for Astrophysics, is looking into the feasibility of detecting moons, particularly large moons, using current technology.

According to simulations by astronomers, the potential for such large moons exists. Based on their study, Earth-sized objects may migrate within forming solar systems and captured by a gas giant. Although some of the new "moons" will not survive as their orbits could crash and they would eventually be ejected, studies showed that around half of these captured moons will be able to live.

The project, "The Hunt of Exomoons with Kepler" or HEK for short, searches for moons through two main methods: the transits such moons may cause and the subtle tugs they may have on previously detected planets.

In the transit method, moons will be detected by Kepler as it passes in front of the disc of the parent star, causing a temporary reduction in its brightness.

This second method is known as Timing Transit Variation (TTV), which is finding the more subtle effect of the moon tugging the planet and changing when the transit begins and ends. It has also been used to infer the presence of other planets in the system creating similar tugs.

The same tugs exerted while the planet is crossing the disk of the star will change the duration of the transit, known as Timing Duration Variations (TDV). The combination of these two variations can give a great deal of information about potential moons including the moon's mass, the distance from the planet, and potentially the direction the moon orbits.

The team is presently working on a list of planet systems that Kepler has discovered that have sufficient data taken, that it be of high quality, and that the planets be sufficiently large to capture such large moons. The planets with these criteria will be searched for possible exomoons, the team said.