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Astronomers have identified a distant planetary system whose unusual arrangement of worlds is forcing scientists to rethink long‑standing assumptions about how planets form.
In our own solar system, the pattern seems straightforward: small, rocky planets orbit close to the Sun, while massive gas giants dominate the outer regions. For decades, researchers assumed this structure was typical across the galaxy.
A newly examined system orbiting the star LHS 1903, located in the thick‑disk region of the Milky Way, now suggests otherwise.
A System That Breaks the Rules
In a collaborative European study, astronomers analyzed data from multiple telescopes and confirmed the presence of three planets orbiting the cool, faint red dwarf. The inner planet is rocky, followed by two gas giants—an arrangement that aligns with conventional expectations.
But new observations from the European Space Agency’s Cheops exoplanet telescope revealed a fourth planet farther out. Surprisingly, this outermost world also appears to be predominantly rocky.
“This system is essentially built from the inside out: first rocky, then gaseous, then gaseous again—and finally another rocky planet on the outside,” said Thomas Wilson, lead author of the study and planetary astrophysicist at the University of Warwick, in an ESA statement.
“Rocky planets don’t normally form that far from their star,” Wilson added.
Rethinking Planet Formation
Traditionally, scientists believe that planets form simultaneously within a massive disk of gas and dust—the protoplanetary disk—that surrounds a young star. Dust grains clump together, grow into larger bodies, and eventually form planetary cores. In the cold outer regions, these cores can accumulate thick atmospheres, becoming gas giants. Closer to the star, intense radiation strips away most of the gas, leaving behind rocky worlds.
To explain the strange architecture of LHS 1903, the research team explored several scenarios. Their leading hypothesis: the planets may not have formed at the same time.
They propose that the outer rocky planet emerged after most of the system’s gas had already dissipated, preventing it from becoming a gas giant.
“And yet here we find a small rocky world that defies all expectations,” Wilson said. “We may be seeing the first evidence of a planet that formed in a largely gas‑free environment.”
A Growing Catalogue of Surprises
Since the 1990s, astronomers have discovered more than 6,000 exoplanets, typically detected by measuring tiny dips in starlight as planets pass in front of their stars. Each new system adds to a growing realization: the universe is far more diverse than early models predicted.
“Our theories of planet formation have historically been based on what we see in our own solar system,” said Isabel Rebollido, a planetary‑disk researcher at ESA. “The more varied exoplanet systems we find, the more we are pushed to rethink those theories.”
The LHS 1903 system now joins a small but growing list of planetary arrangements that challenge the standard narrative—suggesting that the universe still has many surprises in store.
- Hector Pascua with reports from de.euronews.com/picture; pixabay.com
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