Colossal Super-Jupiter Discovered in the Great Bear Constellation

Astronomers have uncovered a massive exoplanet in the Great Bear constellation, significantly expanding our knowledge of planetary diversity.

This newly discovered planet, described as a super-Jupiter, is over 11 times the mass of Jupiter, the largest planet in our solar system. This discovery was made by a team of researchers from the NCU Institute of Astronomy in collaboration with scientists from Spain and the United States, and it offers a unique glimpse into the dynamics of distant planetary systems.

A Massive Planet in a Distant System

The massive exoplanet orbits the star HD 118203, located just over 300 light-years from Earth. This star is about 20% more massive and twice the size of the Sun. While the planetary system was already known to host a smaller gas giant orbiting in a rapid six-day cycle, the recent discovery of the super-Jupiter adds an entirely new dimension to the system. The new planet orbits at a much greater distance, taking about 14 years to complete one full orbit, while maintaining a temperature of -100 degrees Celsius.

Although the super-Jupiter has not been observed directly, its presence was confirmed through radial velocity measurements, which track the subtle wobbles in the star's motion caused by the planet’s gravitational pull. As Gracjan Maciejewski, the leader of the research team, explained, “While the team cannot see the planet itself, they can spot the star around which it orbits.” This indirect detection method provided the critical evidence for the planet's existence.

A Unique Planetary System

The discovery of this hierarchical planetary system adds an exciting chapter to the study of planetary formation. The system's first planet, discovered in 2005, is a hot Jupiter that orbits its star in just six days. This new super-Jupiter, by contrast, takes a much more leisurely path around the star, orbiting every 14 years at a distance of about six astronomical units (AU)—six times the distance between the Earth and the Sun.

The dynamics of this system are particularly intriguing because, despite the gravitational interactions between the two large planets, the system remains stable over long periods. As Krzysztof Goździewski, one of the researchers involved in the study, noted, “We have shown that this is due to effects arising from the general theory of relativity. If it were not for these effects, the planets would behave like jittery springs, constantly changing the shape of their orbits and their orientation in space.” This remarkable stability offers a fascinating case for studying how such massive planetary systems evolve over millions of years.

Patience Leads to Discovery

The identification of the super-Jupiter is the result of nearly 20 years of patient research. Early observations hinted at the presence of another planet in the system, which led the researchers to include HD 118203 in their observational programs. Over time, data collected from telescopes such as the Hobby-Eberly Telescope in Texas and the Telescopio Nazionale Galileo in the Canary Islands helped to confirm the planet’s existence.

It took years of additional work, including detailed Doppler observations, to finally gather enough evidence to confirm the planet’s parameters. As Gracjan Maciejewski emphasized, “Patience pays off. The new observations collected in March 2023 proved crucial in determining the planet’s orbital parameters.” The team’s dedication allowed them to build a complete model of the planetary system and study its complex dynamics in detail.

Insights Into Planetary Formation

The discovery of this super-Jupiter not only adds to the growing catalog of exoplanets but also provides critical insights into how planetary systems, particularly those with massive gas giants, form and evolve. The unique configuration of this system, where one planet is tightly bound to its star while the other orbits farther out, allows astronomers to explore how such systems maintain long-term stability.

As Andrzej Niedzielski, one of the co-authors of the study, pointed out, “Doppler observations indicated that this was not the end of the story, that there might be another planet out there.” His team’s research confirms that this is indeed the case, offering a fresh perspective on planetary systems far beyond our own.

The discovery is expected to prompt further study of the system and may even lead to the identification of additional planetary bodies. This groundbreaking find, published in the journal Astronomy and Astrophysics, deepens our understanding of planetary dynamics and could help refine models of how such massive systems form and evolve over time.