An international team of astronomers has identified a planetary system 116 light-years from Earth that challenges fundamental theories of how planets form. The system, orbiting a star named LHS 1903, features a rocky planet in an outer orbit where a gas giant would be expected, while three gas giants are positioned closer to their star.
The discovery was made using the European Space Agency's CHEOPS space telescope, a mission under the leadership of the University of Bern in collaboration with the University of Geneva. This finding suggests that the architecture of planetary systems across the galaxy may be far more diverse than previously understood.
Key Takeaways
- A new planetary system, LHS 1903, has been discovered 116 light-years away with an unusual configuration.
- A small, rocky planet orbits far from its star, while three gas giants are located in closer orbits.
- This arrangement contradicts the standard model of planet formation, which predicts rocky planets near the star and gas giants farther out.
- The discovery was made by the Swiss-led CHEOPS space telescope, highlighting its precision in detecting exoplanets.
- Researchers propose a new theory of sequential planet formation to explain the system's strange layout.
An Unexpected Cosmic Arrangement
For decades, our own solar system has served as the primary model for planetary architecture. This model shows smaller, dense, rocky planets like Earth and Mars orbiting close to the central star, while massive gas giants like Jupiter and Saturn reside in the colder, outer regions.
The LHS 1903 system turns this concept on its head. The innermost planets are gas giants, worlds that astronomers believed could only form in the frigid outer reaches of a system. Even more puzzling is the presence of a terrestrial, or rocky, planet in the distant outer orbit—a region thought to be the exclusive domain of gas and ice giants.
"Because rocky planets do not normally form beyond gas giants, this planet completely turns our theories upside down," stated Professor Monika Lendl of the University of Geneva.
This discovery forces a re-evaluation of the processes that govern the birth of planets. It adds to a growing list of "strange" exoplanetary systems that do not conform to the neat, orderly model provided by our own cosmic neighborhood.
The Role of the CHEOPS Telescope
The detection of this distant and unusual world was made possible by the high-precision capabilities of the Characterising Exoplanet Satellite (CHEOPS). Led by Swiss institutions, CHEOPS is specifically designed to study known exoplanets and search for new ones by measuring the tiny dips in starlight that occur when a planet passes in front of its star, an event known as a transit.
"It is thanks to the precision of CHEOPS that we were able to detect this new planet," Lendl explained. The telescope's ability to measure these minute changes in brightness allowed the team to not only confirm the planet's existence but also to begin characterizing its properties, leading to the conclusion that it is a rocky world in an improbable orbit.
What is the Standard Model of Planet Formation?
The prevailing theory suggests that planets form from a large, rotating disk of gas and dust known as a protoplanetary disk that surrounds a young star. In this model, all planets within a system are thought to form more or less at the same time. Closer to the star, where temperatures are high, only rocky materials can condense, forming terrestrial planets. Farther out, beyond the "frost line," temperatures are low enough for volatile ices to condense, allowing massive cores to form that can then attract huge amounts of gas, creating gas giants.
A New Theory of Planet Birth
To account for the bizarre layout of the LHS 1903 system, the research team has proposed an alternative theory of planetary formation. Instead of all planets forming simultaneously, they suggest the planets around the small red dwarf star LHS 1903 may have formed sequentially, one after another.
This new hypothesis proposes a timeline for the system's development:
- Early Stage: The two innermost gas giants formed first, when the protoplanetary disk was still rich in gas. They quickly accumulated massive atmospheres, becoming the giants they are today.
- Later Stage: The outer rocky planet formed much later in the system's history. By this time, most of the gas in the disk had dissipated or been blown away by the star's solar wind.
- Result: Without a significant amount of available gas, the late-forming outer planet could not accumulate a massive atmosphere. It remained a smaller, denser, rocky world, despite forming in a region where gas should have been plentiful earlier on.
This "sequential formation" model provides a plausible explanation for how a rocky planet could end up in the outer system, long after the gas giants had established their orbits closer to the star.
LHS 1903 System at a Glance
- Distance from Earth: 116 light-years
- Star Type: Red Dwarf
- Known Planets: At least four
- Key Anomaly: A terrestrial (rocky) planet orbits farther out than three gas giants.
Implications for the Search for Life
The discovery of LHS 1903 is a significant reminder that our solar system is not a universal template. The diversity of planetary systems is far greater than previously imagined, which has profound implications for our understanding of the cosmos and the search for habitable worlds.
According to a statement from the University of Bern, this finding is part of a growing body of observations that challenge established theories. It underscores that nature has multiple ways to build planetary systems, many of which look nothing like our own.
As telescopes like CHEOPS and the James Webb Space Telescope continue to scan the skies, they are revealing a universe filled with an astonishing variety of worlds. Each unusual system like LHS 1903 provides a crucial piece of the puzzle, helping scientists refine their models and better understand the conditions under which planets—including potentially life-bearing ones—can form and evolve.
The ongoing work by researchers at the Universities of Bern and Geneva continues to place Switzerland at the forefront of exoplanet research, pushing the boundaries of what we know about the worlds beyond our solar system.