Scientists have dubbed that moons escape their planets and become liberated worlds “ploonets,” and say that current telescopes may be able to find the wayward objects.
Astronomers think that exomoons orbiting planets that orbit stars other than the sun should be common, but efforts to find them have turned up empty so far .
The combined gravitational forces of the planet and the star would inject extra energy into the moon’s orbit, pushing the moon farther and farther from its planet until eventually it escapes, the researchers report.
Some ploonets may be indistinguishable from ordinary planets. Others, whose orbits keep them close to their planet, could reveal their presence by changing the timing of when their neighbor planet crosses, or transits, in front of the star.
The ploonet should stay close enough to the planet that its gravity can speed or slow the planet’s transit times. Those deviations should be detectable by combining data from planet-hunting telescopes like NASA’s TESS or the now-defunct Kepler, Sucerquia says.
Ploonethood may be a relatively short-lived phenomenon, though, making the worlds more difficult to spot. About half of the ploonets in the researchers’ simulations crashed into either their planet or star within about half a million years. And half of the remaining survivors crashed within a million years.
The study is a good first step for thinking about what would happen to exomoons in real planetary systems.