ESA/CC BY-SA 3.0 IGO
Artist’s illustration of the planetary system around the star LHS 1903
The discovery of a fourth rocky planet in the system around red dwarf LHS 190 challenges the long-held theory that the planets furthest from the star are gaseous.
Astronomers have discovered a distant planetary system that challenges long-held assumptions about how worlds form, revealing a star whose planets are arranged in a surprising order.”from the inside out“.
In our own Solar System, the pattern appears orderly: the four inner planets are small and rockywhile the outer four are massive gas giants. For decades, scientists believed that this basic structure — rocky planets close to the star and gas giants farther away — was a common model throughout the universe.
But new observations of the red dwarf star LHS 1903 suggest that nature may be more creative.
An international team of researchers had previously identified three planets orbiting LHS 1903, located in the thick disk of the Milky Way. The system initially seemed conventional: a rocky planet closest to the star, followed by two gas giants. This configuration was in accordance with standard models of planetary formation.
However, additional analysis using the European Space Agency’s CHEOPS (Characterizing Exoplanet Satellite) revealed a fourth, more distant planet, which is also rocky, says .
“This makes this an inverted system, with a planetary order of rocky, gaseous, gaseous and then rocky again,” said Thomas Wilson, lead author of the published in the journal Science. Wilson, planetary astrophysicist at the University of Warwick.
According to the prevailing theory, planets form within a rotating protoplanetary disk of gas and dust around a young star. The intense radiation near the star removes gases lighter, leaving rocky and compact worlds behind. Further away, where it is colder, planetary cores can accumulate dense atmospheres of hydrogen and helium, growing to become gas giants.
The outermost rocky planet in the LHS 1903 system challenges this model. After ruling out alternative explanations, the researchers proposed a new scenario, in which the planets could have formed sequentially, rather than simultaneously. In this model, when the fourth planet began to form, most of the gas in the system had already dissipated. Without enough gas to build a dense atmosphere, the distant world remained rocky.
“We appear to have found the first evidence of a planet that formed in what we call a low gas environment,” said Wilson.
Isabel Rebollido, a planetary disk researcher at the European Space Agency, said the growing diversity of exoplanetary systems is leading scientists to rethink traditional theories training.
The unusual architecture of LHS 1903 contributes to this change, suggesting that planetary systems may arise through a wider range of processes than previously imagined.
