14 DAY TRIAL // Most of the astronomical community today is keeping its eyes focused on the goal of finding Earth-like planets on the desired orbits around their parent stars, in systems thousands of light-years away. But a new group inside the community is arguing that a habitable world may also be identified in a moon circling a Jupiter-sized exoplanet, revolving around a yellow dwarf inside the habitability zone. In fact, some experts say, we may have a better chance of populating an exomoon before we even set foot on an exoplanet.
But detection – which is difficult enough to do for larger planets – is the main element that could stand in the way of us colonizing such a celestial body. At this point, the existence of planets outside of our solar system is inferred by observing variations in a star's brightness, and then analyzing if they were determined by an object with a stable orbit (an exoplanet), or by a passing meteor or comet. Rigorous observations are then required in order to determine the mass the planet has, as well as the defining traits of its orbit. And, even then, in most cases the body is too close to the star, or too far away.
A possible way of detecting an exomoon would be to look for transit timing variations (TTV) in its planet's orbit. Even in the case of the Earth and the Moon, the two revolve around a common center of gravity, which itself then spins around the Sun. Each time the Moon comes full circle around our home, it triggers a small wobble in our planet's trajectory, which is precisely TTV. Future generations of incredibly powerful, space-based observatories could sport instruments advanced enough to detect these minute changes from thousands of light-years away.
However, astronomers know how many exoplanet detections are false alarms, so some of them set out to create a foolproof way of identifying the real deal. Among them is David Kipping, from the Cambridge-based Harvard-Smithsonian Center for Astrophysics. He determined that, in addition to the TTV, exomoons also produced another signal, as the moons changed the duration of the transit for their parent planets. Together, these two signals can accurately identify a target object as an exomoon, and not as some other, random astronomical event, Technology Review reports.