The moon has been Earth’s companion for as long as humanity remembers, although how it formed remains a mystery. Now a new hypothesis looks at a new type of celestial world known as a “ploonet,” and scientists believe our moon could leave Earth’s neighborhood and become one.
Ploonets are former moons that have been separated from their host planet’s orbit and instead begin orbiting their system’s host star. While the existence of ploonets hasn’t yet been proven, it could explain some astronomical events which scientists previously weren’t able to explain.
One of those phenomena includes hot Jupiters, which are exoplanets similar to our solar system’s Jupiter, but they’re hot because they orbit extremely close to their host stars. However, some scientists believe such planets formed toward the outside of their star systems and then migrated inward as time passed.
Now a new study available on the pre-print website arXiv suggests that objects called ploonets could explain this phenomenon. Scientists described a set of detailed simulations which could explain what would happen if a hot Jupiter began to migrate toward its host star with an exomoon.
The simulations suggested that 48% of the exomoons would escape their host planet and start orbiting the host star instead as a ploonet. Additionally, if the moon had an icy surface, the water would evaporate as it escapes, explaining the comet-like tail. If such a ploonet passed its host star, scientists could understand why some stars flicker.
Ploonets could also explain some more unusual astronomical phenomena. For example, if a moon that became a ploonet eventually crashes into its former neighbor, it would create space debris which could explain how rings around some planets formed.
“Those structures [rings and flickers] have been discovered, have been observed,” researcher Mario Sucerquia told Science News. “We just propose a natural mechanism to explain [them].”
Ploonets could also explain why researchers haven’t found any definitive evidence of exomoons, despite theories suggesting that the universe should be full of them. For example, moons could escape their planet’s orbit before scientists can detect them.
Scientists believe ploonets don’t have long lifespans. They suggest that about 50% of ploonets crash into their host planet within half a million years, while the other 50% meet the same fate within less than a million years.
But what about Earth’s moon? Sucerquia told Science News that our moon “is a potential ploonet,” because it gets 4cm (around 1.5 inches) away from Earth every year. Nevertheless, there’s no need to worry about the moon becoming a ploonet anytime soon. Scientists say it could take at least another 5 billion years for that to happen if it ever does.