Topic: Space

Astronomers found a planetary system around a small star called LHS 1903. The planets are arranged in an unusual order, with rocky planets closer to the star and gas giants farther away.

Children often learn the order of the planets in our Solar System using quirky memory phrases like 'My Very Educated Mother Just Served Us Nachos.' These sayings help recall Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. In our Solar System, the planets fall into two broad groups. The inner planets closest to the Sun, from Mercury through Mars, are rocky worlds. Farther out are the giant gaseous planets, from Jupiter to Neptune. Astronomers have long believed this arrangement reflects a common pattern throughout the Universe. According to leading theories of planet formation, rocky planets form near their star while gas giants develop farther away where cooler conditions allow thick atmospheres to build up. Observations of many planetary systems have generally supported this idea. But a newly studied star system called LHS 1903 may challenge that understanding.

The team led by Thomas Wilson from the University of Warwick in the United Kingdom combined observations from several space and ground-based telescopes to examine planets orbiting the star. The team identified three planets at first. The closest planet appeared rocky, while the next two seemed gaseous. That arrangement matched what scientists expected to see. Then researchers analyzed data from the European Space Agency's CHaracterising ExOPlanet Satellite (Cheops) and uncovered something unexpected. A fourth planet orbiting farther from the star appeared to be rocky as well.

'Rocky planets don't usually form so far away from their home star,' says Thomas. Current models suggest rocky planets form near stars because intense radiation strips away gas surrounding developing planetary cores. Farther away, cooler temperatures allow gas to accumulate into thick atmospheres, creating giant gaseous planets. ESA Cheops project scientist Maximilian Günther says the discovery highlights how much scientists still do not understand about planetary origins.

Scientists Test Possible Explanations Researchers did not immediately conclude that existing planet formation theories were wrong. Instead, they explored whether other events could explain the unusual system. One possibility was that the outer rocky planet had once possessed a thick atmosphere that was later blasted away by a collision with a massive asteroid, comet, or another large object. Another idea was that the planets may have changed positions over time.

Using simulations and calculations of the planets' orbital behavior, the team ruled out those explanations. Their investigation instead pointed toward a more unusual possibility. The planets around LHS 1903 may not have formed simultaneously. Instead, they may have developed one after another.

Why It Matters

This discovery can help scientists better understand how planets form and evolve, which is crucial for understanding our own Solar System and the possibility of finding life beyond Earth.

Key Facts

• A team led by Thomas Wilson from the University of Warwick in the United Kingdom discovered a planetary system around LHS 1903 that challenges existing theories of planet formation.
• The planets are arranged in an unusual order, with rocky planets closer to the star and gas giants farther away.
• The discovery suggests that the planets may not have formed simultaneously, but rather developed one after another.

Key Terms

Protoplanetary discs

Giant discs of gas and dust around stars where planets form

Implications

This discovery can help scientists better understand how planets form and evolve, which is crucial for understanding our own Solar System and the possibility of finding life beyond Earth.