A research team, which has included professors from The University of St Andrews, has made new astrological discoveries which challenge our current understandings of planet formation and evolution.
An international research team has been observing a unique planet system around the star TOI-178, which is 200 light years away from Earth. Researchers originally believed that only three planets were orbiting the star TOI-178. On 25 January 2021, Astronomy and Astrophysics published that they had discovered three more planets and that five of these six planets orbited their star in a harmonic rhythm.
The joint commission led by the European Space Agency (ESA), included researchers from the University of Bern, the University of Geneva and The University of St Andrews. The team made observations using the CHEOPS (Characterising ExOPlanets Satellite) space telescope, launched in December 2019, as part of the efforts to precisely measure the size of the known planets.
Dr Thomas Wilson, from the School of Physics and Astronomy at The University of St Andrews, research fellow in the Centre of Exoplanet science and co-author of the paper published in Astronomy and Astrophysics described the discovery.
He stated, “When we started studying this planetary system we thought that there were three planets orbiting TOI-178 based on observations with NASA’s Transiting Exoplanet Survey Satellite (TESS), but we were unsure what we would find with closer inspection using CHEOPS. With 11 days of high-quality data it quickly became apparent that there were at least five planets in a special resonance chain of orbits.”
In the case of the six planets around TOI-178, all but one are locked in a rare rhythm as they move in their orbits. This means that they are in resonance. The patterns formed by the planet’s orbits repeat themselves rhythmically as the planets move around the star, with some planets aligning every few orbits.
Professor Andrew Collier Cameron, Professor of Astronomy in the Centre for Exoplanet Science in the School of Physics and Astronomy at the University of St Andrews, who led the mission’s data-analysis team, explained, “The chain of resonances between the planets in the TOI-178 system is a remarkable fossil clue to the entire system’s formation process. This orderliness has allowed these closely-packed planets to avoid catastrophic interactions with each other for billions of years.”
The ratio of their orbital period from simple fractions, with the planets following a 18:9:6:4:3 pattern. This pattern translates into a regular harmonious motion; while the second planet from the star (first in the pattern) completes 18 orbits, the third planet from the star (second in the pattern) completes nine orbits, and so on.
The movements of the five planets in the system create a kind of music as represented in a video published by the European Southern Observatory. This video can be found using the following link: https://www.youtube.com/watch?v=-WevvRG9ysY&feature=emb_logo
The configuration of this unique planetary system challenges our current understanding of planet formation and evolution. Typically, closely packed planets orbiting a star in such a unique manner decrease in density the further away they are from the star. However, in the case of the planetary system surrounding TOI-178 the density of the planets is far more irregular, despite the harmonic, orderly manner they orbit around their star. A similar resonance is observed in the orbits of three of Jupiter’s moons, yet the resonant motion in the TOI-178 is much more complex as it involves five planets.
ESA Project Scientist Kate Isaak, said, “It is the first time we have observed something like this. In the few systems we know with such a harmony, the density of planets steadily decreases as we move away from the star. In the TOI-178 system, a dense, terrestrial planet like Earth appears to be right next to a very fluffy planet with half the density of Neptune followed by one very similar to Neptune.”
The outer four planets are gaseous and have densities similar to Neptune and Jupiter, while the inner two have terrestrial (earth-like) densities.
Further information on this discovery, alongside the research article published in Astronomy and Astrophysics can be accessed via their website: