An Unusual Planetary System Discovered That Challenges Classical Theories of Planet Formation

Astronomers, using telescopes from NASA and the European Space Agency (ESA), have discovered an unusual planetary system, LHS 1903, orbiting a red dwarf — the most common type of star in the Universe.

The system consists of four planets and has an extremely atypical structure. The planet closest to the star has a rocky composition. It is followed by two gas giant planets. However, most unexpectedly, the farthest — the fourth — planet turned out to be rocky again.

This arrangement contradicts the widely accepted model of planet formation, according to which rocky planets usually form near a star, while gas giants form farther away. Our Solar System is structured in this way.

According to classical theory, planets form from a protoplanetary disk of gas and dust around a young star. The inner regions of the disk are too hot, so only rocky bodies can form there. Farther from the star, temperatures are lower, allowing ice and other compounds to freeze, form massive cores, and then attract gases — leading to the formation of gas giants.

Researchers paid special attention to the outer rocky planet LHS 1903 e, whose radius is approximately 1.7 times that of Earth. Dynamic analysis showed that it did not form as a result of collisions between other bodies and is not a “stripped” gas giant that lost its atmosphere.

Scientists suggest that the system may have formed under a so-called “gas-poor” scenario. According to this hypothesis, the planets formed sequentially — from the inside outward. By the time the outermost planet formed, there may not have been enough gas left in the disk for it to become a giant.

LHS 1903 is considered an important “laboratory” for studying alternative planet formation scenarios. Some experts suggest that the outer rocky planet may have an unusual atmosphere. Future observations, including those using the James Webb Space Telescope, will help test this.

The study emphasizes that planet formation processes are far more complex than previously thought, and discoveries like this could significantly change our understanding of planetary system structures in the Universe.