Six-planet system discoveredDate: 21 April 2020 Tags: Space
Researchers have discovered a star system with six planets whose orbits are in almost perfect rhythm.
The star, dubbed HD 158259, is orbited by a "super-Earth" and "five mini-Neptunes”. Astronomers only know of around dozen star systems containing six or more planets. However, what makes the HD 158259 system so remarkable is the exceptionally regular spacing of its planets.
Using measurements taken using the SOPHIE spectrograph and the TESS exoplanet-hunting space telescope, an international team of researchers were able to precisely calculate the orbits of each planet.
All pairs of subsequent planets in the system are said to be close to the "3:2 resonance." This essentially means that as the first planet, or the one closest to the star, completes three orbits; the second one completes roughly two orbits. And as the second planet completes three orbits, the third completes roughly two. This pattern continues for all the subsequent planets.
These intriguing orbital periods could provide scientists with clues as to how the system formed, suggesting that they did not form close to their current positions.
The evidence indicates that the star system is compact, highlighted by the fact that the distance between the outermost planet and HD 158259 is 2.6 times smaller than the distance between the sun and Mercury in our own solar system.
The planets of the system, which is located around 88 light-years away, appear to have masses between two and six times that of the Earth's.
Five of them are defined as super-Earths, meaning that they have a mass higher than that of our planet but significantly lower than Uranus or Neptune.
The remaining planet is described as a "mini-Neptune”, planets that are less massive than Neptune while still resembling the gas giant in our own solar system in terms of atmosphere and composition.