Our own solar system is an exciting place, particularly when it comes to the search for alien life. Around Saturn and Jupiter orbit the gas giants Titan, Enceladus and Europa, three of the most interesting worlds we currently know about but who is to say that this isn’t the same in other solar systems?
A paper published in 2015 regarding the preprint server arXIv argues that moons surrounding Jupiter-sized exoplanets may be the most likely places for life to develop and while finding such exomoons has been a difficult task so far, some are relatively easy to spot.
While planets bigger than our solar system’s own biggest planet Jupiter might not support life, if each has multiple moons it creates a better chance of finding one where conditions are just right. Up to now, the closest we’ve come to discovering such a place is in a star system that’s 4,000 light years away – a moon that orbits the exoplanet Kepler-1635b – but authors of the paper that suggest this are cautious.
It’s still incredibly difficult to find an exomoon and the best way astronomers currently have to do so is by using something called the transit method. This involves studying light that reaches us from stars and waiting for periodic dips in brightness that would happen when a planet passes in front of a star.
A potential moon is found by working out how the orbit of the exoplanet would be affected if it had a moon and they do this by studying the time in between dips. However, as we know from our own solar system, a planet could have as many as 50 moons and other planets in the system may change the orbit. This makes the whole process incredibly complex.
In the arXIv paper, authors Heller and Pudritz explain “Exomoons represent an outstanding challenge in modern astronomy, with the potential to provide rich insights into planet formation theory and habitability.” However, just because our solar system has plenty of moons does not mean the same will be repeated elsewhere. Take, for example, the fact that in other solar systems Earth-like planets are incredibly rare while planets the size of Neptune but close to their star are incredibly common.
The paper states that if the moons are big enough, the next generation of Space telescopes should be able to spot them. For example, planets that are 15 to 30 times the size of Jupiter could be home to moons that are bigger than the smallest exoplanet we’ve already discovered. These are big enough that experiments such as the ESA’s Planetary Transits and Oscillations of stars (PLATO) spacecraft, due for launch in 2026, may even spot them.
