A group of astronomers from Western University has reported discovering six potential exomoons in distant star systems in the galaxy. The exomoons are located in star systems know as Kepler Object of Interest (KOOI); Kepler 517b (KOI-303.01), Kepler 1000b (KOI-1888.01), Kepler 409b (KOI-1925.01), Kepler 1326b (KOI-2728.01) and Kepler 1442b (KOI-3220.01).
Exoplanets orbit stars other than our Sun; The moons of these planets are called exomoons. While more than 4,000 exoplanets have been discovered since the mid-1990s, none have a confirmed moon orbiting them, although several major candidates have been identified in recent years.
Our own solar system contains hundreds of moons. If alien moons are prolific around other stars, they also greatly increase the potential places where life could sustain itself, and where humanity might one day venture out into.
The exomoon candidates and their characteristics have been presented by the astronomers from the Institute for Earth and Space Exploration in the journal Monthly Notices of the Royal Astronomical Society.
“We know thousands of exoplanets in our galaxy, the Milky Way, but we only know a handful of ex-moon candidates,” revealed professor of physics and astronomy, Paul Wiegert, and co-author of the study.
At a distance of 200 to 3,000 light-years away, the exoplanets reported in the new study were discovered using data from the Kepler Space Telescope, a planet-hunting spacecraft decommissioned by NASA in 2018.
The exoplanets were revealed by transit method or Transit Photometry, a method that measures the light curve of stars for periodic dips in brightness, when cosmic objects such as planets pass between us and the star. Their moons, however, were not so easily seen.
“These exomoon candidates are so small that they cannot be seen from their own transits. Rather, their presence is revealed by their gravitational influence on their parent planet,” explained Wiegert.
If an exoplanet orbits its star undisturbed, the transits it produces occurs precisely at fixed intervals. But for some exoplanets, the transit time is variable, sometimes occurring several minutes before or after. Such variations in transit time, known as TTV, indicate the existence of another body. That could mean a moon or another planet in the system that affects the planet in transit.
Since exoplanets are more massive than exomoons, most of the TTVs observed to date have been related to the influence of other exoplanets.
But now, astronomers have discovered six Kepler exoplanet systems whose TTVs are equally well explained by exomoons as for exoplanets.
“That is why we are calling them ex-moon ‘candidates’ right now, as they still need follow-up confirmation,” Chris Fox, a Physics and Astronomy Ph.D. candidate who made the discoveries explained in a statement.
Confirming their existence is a though one for astronomers since telescopes needed to confirm the existence of the exomoons have still not been produced, which means that astronomers will need to rely on other types of data to revise their discoveries.
Nonetheless, astronomers can say that the six new systems are entirely consistent with exomoons.
“Their masses and orbits are such that they would be stable; they would be small enough that their own transits wouldn’t be seen, and they reproduce the pattern of TTVs seen throughout the entire Kepler data set,” Fox revealed.