Ploonets — large regular moons ejected from orbits around close-in gas giant exoplanets — could explain many baffling astronomical observations, such as the puzzling behavior of a star called KIC 8462852 (also known as Tabby’s star), the anomalous features of the Kronos-Krios binary stellar system, and the hypothetical exocometary signatures around stars KIC 12557548 and KIC 3542116.
An artist’s impression of a gas giant exoplanet with its large exomoon. Image credit: Sci-News.com.
A team of astronomers led by Universidad de Antioquia’s Dr. Mario Sucerquia modeled the likely behavior of large moons predicted to form around massive exoplanets — and discovered that they would be expelled and sent packing.
About 50% of these ejected objects would survive both the immediate expulsion and avoid any subsequent collision with the planet or the host star, ending up as ploonets — quasi-planets traveling around the star, but in eccentric Pluto-like orbits.
“These moons would become planetary embryos, or even fully-fledged planets, with highly eccentric orbits of their own,” said co-author Jaime Alvarado-Montes, an astronomer at Macquarie University.
While conceding that ploonets remain hypothetical, their existence would offer a possible explanation for several challenging results produced by NASA’s Kepler Space Telescope.
These include the puzzling dips in the light-curves emanating from the KIC 8462852 star.
“It’s better known as Tabby Star, and the strange changes in its light intensity have been observed for years, but are still not understood. Ploonets could be the answer,” Alvarado-Montes said.
They might also explain apparent evidence of planetary cannibalism in the Kronos-Krios system, or the existence of exocomets around other stars.
Ploonets, thus, may be a vital piece of the planetary puzzle, but, as yet, their existence remains unproven.
“Even if ploonets do exist, they may deteriorate too rapidly to ever be observed,” the astronomers said.
“If, on the other hand, the timescales are large enough, we could have real chances to detect them in the near and middle future.”
The study will be published in the Monthly Notices of the Royal Astronomical Society.
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Mario Sucerquia et al. 2019. Ploonets: formation, evolution, and detectability of tidally detached exomoons. MNRAS, in press; arXiv: 1906.11400
