Astronomers have found a population of unique planetary systems consisting of isolated worlds.
These molten worlds, known as "hot Earths," are located too far away from its other siblings or are uniquely the only planets in their own systems. Kepler-10b, one of the most famous of these hot Earths discovered in 2011, has a companion: a giant planet located far away.
Exoplanetary systems are different from the solar system in terms of architecture or how close the alien planets orbit each other and their stars. A system either consists of a solitary planet or planets that are too far away from each other.
"In the solar system, and among most of the planetary systems discovered by Kepler, planets tend to be pretty close together," Jason Steffen, an astronomer at the University of Nevada in Las Vegas and author of the study, said in a report by Space.com. "Our nearest neighbor would be beyond the orbit of Saturn. It takes something unusual to produce such a wide separation between neighboring planets."
Steffen and Jeffrey Coughlin from the SETI Institute in California analyzed the most recent data on 3,063 candidate exoplanets in 2,373 systems from NASA's Kepler Space Telescope to investigate the differences between single and multiplanet systems. The data include 1,890 candidates in single-planet systems and 1,173 candidates in 483 multiplanet systems. Through identifying the uniquely isolated exoplanetary system, the researchers could explain how they could work. The results of the study are published in the Proceedings of the National Academy of Sciences (PNAS).
The study focused on 144 hot-Earth exoplanets, whose orbits are closest to their star. Because of their proximity to their stars, the planets take only about one Earth day to revolve around their star. Out of the 144 exoplanets, the scientists found that 24 of them orbit without another planet nearby, which makes them unique compared with multiplanet systems. The researchers suggested that
According to the researchers, these hot Earths may have come from the cores of hot giant planets or "hot Jupiters" after their atmospheres have burned off due to their proximity to their star. Previous studies suggested that hot Jupiters formed in the distant and cooler regions of their systems, but moved inwards and knocking other planets until they finally slowed and settled into orbit around their star. This explains why the Kepler-10b system consists of a hot Earth and a distant giant planet.
Steffen said that future research could shed light on how commonly lonely hot Earths occur and how they were formed, such as the ongoing extended Kepler mission (K2) and NASA's Transiting Exoplanet Survey Satellite (TESS).
"The advantage that K2 and TESS bring is that they will find hot Earths orbiting much brighter stars," Steffen said in a statement.