For decades, astronomers believed that Hot Jupiters—giant planets orbiting perilously close to their stars—were solitary wanderers, either consuming or ejecting neighboring planets during their migration. However, a groundbreaking study led by the University of Geneva (UNIGE) has turned this long-held belief on its head. The discovery of the unique planetary system WASP-132 has revealed a striking configuration: a Hot Jupiter, a Super-Earth even closer to the star, and a distant icy giant coexisting peacefully.

This remarkable finding, published in Astronomy & Astrophysics, was the result of a collaboration between UNIGE, the National Centre of Competence in Research (NCCR) PlanetS, the Universities of Bern and Zurich, and other international institutions.

A New Perspective on Hot Jupiters

Hot Jupiters, with masses comparable to Jupiter but orbits far closer to their stars than Mercury to the Sun, have long puzzled astronomers. The hostile environment near their stars lacks the gas and dust necessary for their formation, suggesting they must form farther out and migrate inward. Previously, this migration was thought to disrupt any neighboring planets, leaving the Hot Jupiter isolated.

The WASP-132 system, however, has shattered this assumption. Observations show that its Hot Jupiter orbits its star in just over seven days, while a rocky Super-Earth completes its orbit in a mere 24 hours. Beyond them lies a massive icy planet, five times the mass of Jupiter, completing its orbit in five years. Adding to the intrigue, a likely brown dwarf orbits even farther out, making WASP-132 a multi-planetary system unlike any previously observed.

“A Cosmic Laboratory”

“This is the first time we’ve observed such a configuration,” says Solène Ulmer-Moll, a co-author of the study and postdoctoral researcher at the time. François Bouchy, an associate professor at UNIGE, called the WASP-132 system “a remarkable laboratory” for studying planetary formation and evolution.

The discovery challenges traditional theories of Hot Jupiter migration. Instead of chaotic gravitational interactions that would destabilize neighboring planets, WASP-132 suggests a more stable, orderly migration through a proto-planetary disc. This scenario allows the planets to coexist, preserving the system’s architecture.

Decades of Observations Yield Breakthrough

The WASP-132 story began in 2006 with the Wide-Angle Search for Planets (WASP) program. In 2012, over 23,000 photometric measurements identified a candidate planet, WASP-132b, confirmed two years later as a Hot Jupiter with a mass of 0.41 Jupiters.

The turning point came in 2021, when NASA’s TESS space telescope detected a signal from an inner planet—a Super-Earth with a 24-hour orbital period. Using the HARPS spectrograph in 2022, scientists measured its mass and density, revealing a rocky planet six times heavier than Earth. The system’s distant icy giant was identified through the CORALIE spectrograph.

“This discovery was particularly exciting,” says Nolan Grieves, the study’s lead author. “We used intensive signal processing to determine the Super-Earth’s composition, which turned out to be remarkably similar to Earth’s.”

Redefining Planetary Science

The unique arrangement of WASP-132 is reshaping our understanding of planet formation. The system’s Hot Jupiter has a heavy element enrichment of 17 Earth masses, consistent with current models of gas giant formation, while the Super-Earth is composed primarily of metals and silicates.

“The presence of a Hot Jupiter alongside an inner Super-Earth and an outer giant planet provides valuable insights into migration processes,” explains Ravit Helled, professor at the University of Zurich.

As ESA’s Gaia satellite continues its precise measurements of the WASP-132 system, astronomers anticipate more surprises. This discovery underscores the need for long-term, high-precision observations to unlock the complexities of planetary systems.

A Universe of Possibilities

The WASP-132 system is more than an astronomical oddity—it’s a glimpse into the diversity of planetary systems in the universe. As scientists continue to unravel its mysteries, it serves as a reminder that the cosmos is far more complex—and fascinating—than we ever imagined.