Ellen Phiddian
Cosmos science journalist
Astronomers have found a trio of exoplanets which contradict our understanding of how these planets form.
The planets, which orbit around the star WASP-132, consist of a “hot Jupiter,” an inner “super-Earth,” and a huge planet much further out.
Hot Jupiters – gas giants with orbits super-close to their suns – were once thought to be solitary exoplanets.
Their big size was theorised to either fling away, or absorb, any nearby planets.
It was also thought they formed in the outer reaches of a solar system and migrated in, because they shouldn’t form so close to a star.
But the WASP-132 system throws that migration theory into doubt.
“The discovery of a Hot Jupiter alongside an inner Super-Earth and a distant giant planet calls into question our understanding of the formation and evolution of these systems,’’ says Associate Professor François Bouchy, an astronomer at the University of Geneva, Switzerland, and co-author on a paper published in Astronomy and Astrophysics.
In 2016 it was confirmed that WASP-132 had a hot Jupiter, WASP-132b, which zooms around its star every 7 days and 3 hours. WASP-132b is 0.87 times the diameter of Jupiter.
Then, in 2022, the researchers found a rocky super-Earth orbiting even closer to the star. This planet, WASP-132c, is 1.8 times the size of Earth and circles the star in a mere 24 hours and 17 minutes.
“The detection of the inner Super-Earth was particularly exciting,” says first author Dr Nolan Grieves, who did the research at the University of Geneva.
“We had to carry out an intensive campaign using HARPS [the High Accuracy Velocity Planet Searcher in Chile] and optimised signal processing to characterise its mass, density and composition, revealing a planet with a density similar to that of the Earth.”
Now, they’ve confirmed the existence of a third planet in the system, much further out. This planet, which orbits every 5 years, is huge – in fact the researchers think it could possibly be a brown dwarf, sitting between planet and star status.
“This is the first time we have observed such a configuration!” says co-author Dr Solène Ulmer-Moll, who worked on the research at the University of Geneva and the University of Bern.
“The combination of a Hot Jupiter, an inner Super-Earth and an outer giant planet in the same system provides important constraints on theories of planet formation and in particular their migration processes,” says Professor Ravit Helled, from the University of Zurich, Switzerland.
“WASP-132 demonstrates the diversity and complexity of multi-planetary systems, underlining the need for very long-term, high-precision observations.”
