Astronomers have spotted a strange planetary system 117 light-years away that challenges current ideas about how planets form. The system, around a small star named LHS 1903, has four planets: two rocky and two gaseous. But the order is unusual. The closest planet to the star is rocky, the next two are gas giants, and surprisingly, the farthest one is rocky again. The star is a red dwarf, half as massive and less bright than our sun. According to Thomas Wilson from the University of Warwick, "The planet-formation paradigm states that planets close to their host star should form small and rocky, with little-to-no gas or ice," because it's too hot and atmospheres get stripped away. Usually, planets farther out form with lots of gas creating gas-rich worlds. But this system defies that. Wilson calls it "a system built inside-out." In our solar system, inner planets are rocky, outer ones are gaseous. All four planets here orbit closer to their star than Mercury does to the Sun. The two rocky planets are super-Earths—rocky and 2 to 10 times Earth's mass. The gas planets are mini-Neptunes, smaller than Neptune but bigger than Earth. Researchers think these planets didn’t form all at once. The fourth rocky planet probably formed later when gas was running low, making it a "late bloomer." Wilson said, "There was actually not so much material to build this planet." Another idea is the rocky planet lost its gas atmosphere after a collision, similar to theories about how Earth’s moon formed. Andrew Cameron of the University of St Andrews said, "Did it suffer a collision which stripped its atmosphere away? The latter sounds fanciful until you remember the Earth-moon system appears to be a product of just such a collision." The fourth planet is also of interest for habitability. It is 5.8 times Earth’s mass and has a temperature around 60ºC, close to Earth’s hottest recorded temperature of 57ºC. Wilson noted, "It’s definitely possible that this planet is habitable. Future James Webb Space Telescope observations could reveal more."