The discovery of two new planets beyond our solar system by a team of astronomers from The University of Warwick and the University of Geneva (UNIGE), is challenging scientific understanding of how planetary systems form.
The existence of these two exoplanets - an inner super-Earth and an outer icy giant planet - within the WASP-132 system is overturning accepted paradigms of how 'hot Jupiter' planetary systems form and evolve.
Hot Jupiters are planets with masses similar to those of Jupiter, but which orbit closer to their star than Mercury orbits the Sun. There is not enough gas and dust for these giant planets to form where they are observed, so the accepted theory is that they originate far from their star and migrate inward as the planetary system evolves.
Until now, hot Jupiters were thought to orbit their star alone, as migration towards the star would eject other planets in the system. The research team's recent observations of two extra planets in the WASP-132 system now calls into question this theory.
David Armstrong, Associate Professor of Physics, The University of Warwick said, "The detection of the inner super-Earth was exciting as it's particularly rare to find planets interior to hot Jupiters. We carried out an intensive campaign with state-of-the-art instruments to characterise its mass, density and composition, revealing a planet with a density similar to that of the Earth".
This planetary discovery adds a layer of complexity to the WASP-132 system as migration of a hot Jupiter towards its star through dynamical perturbation would destabilise the orbits of the other two planets. This suggests a more stable 'cool' migration path for the hot Jupiter in a proto-planetary disc that surrounds a young star and is the site of planet formation.
"The WASP-132 system is a remarkable laboratory for studying the formation and evolution of multi-planetary systems. The discovery of a hot Jupiter alongside an inner super-Earth and a distant giant calls into question our understanding of the formation and evolution of these systems. This is the first time we have observed such a configuration", says François Bouchy, Associate Professor, Department of Astronomy, UNIGE Faculty of Science.
The hot Jupiter orbits its star in seven days and three hours; the super-Earth (a rocky planet six times the mass of the Earth) orbits the star in just 24 hours and 17 minutes; and the icy giant (five times the mass of Jupiter) orbits the host star in five years. The precise measurements of radius and mass have also made it possible to determine the density and internal composition of the planets. The super-Earth composition is dominated by metals and silicates, similar to that of Earth.
Observations of WASP-132 continue, with the ESA's Gaia satellite measuring minute variations in the positions of stars since 2014, with a view to revealing their planetary companions and outer brown dwarfs.
The full paper is a collaboration between Warwick and the University of Geneva and can be read in Astronomy & Astrophysics: 2025, A&A, 693, A144
DOI: 10.1051/0004-6361/202348177
