Stars far smaller than the Sun can still host giant planets like Jupiter, a fact that researchers at University College London are carefully weighing. Like other worlds, gas giants form from protoplanetary disks that encircle young stars. Current theories describe a two-step process: a solid core grows through rocks, ices, and other heavy solids, and once the core reaches roughly 15 to 20 Earth masses, it begins to pull gas from the surrounding disk. Yet the prevailing view has been that low-mass stars, with their smaller disks, might not have enough material to form a gas giant. This long-held assumption is now being questioned by fresh observations.
A dedicated space telescope built to detect exoplanets using the transit method—which looks for tiny dips in starlight when planets pass in front of their host stars—has identified a surprising example that challenges the established rule. In a comprehensive study, scientists analyzed light curves from 91,306 low-mass stars. Within this dataset they found 15 events where a gas giant briefly crossed the stellar disk, causing a characteristic dimming. In one striking case, a gas giant orbited a star five times lighter than the Sun, a discovery that broadens the known range of planet-forming environments and the types of systems capable of hosting giant planets.
These findings invite scientists to revisit the dominant core accretion model. A growing idea suggests that gas giants may arise not only from the slow buildup of a solid core followed by rapid gas accretion, but also from gravitational instability within the protoplanetary disk. In this scenario, the disk becomes gravitationally unstable and fragments into clumps of dust and gas, each of which could collapse into a planet-sized body. If such instability occurs in the disks of low-mass stars, it could yield exceptionally large gas giants, potentially two to three times the mass of Jupiter, even around stars with relatively modest masses. This viewpoint helps explain the presence of massive planets in environments once deemed unlikely and underscores the broad spectrum of planet formation pathways that can operate under different stellar conditions.
Earlier observations by advanced space telescopes have hinted at diverse planetary systems. In particular, recent findings from the James Webb Space Telescope revealed atmospheres and atmospheric phenomena on distant worlds that broaden the understanding of planetary composition and climate. The emerging picture emphasizes that gas giants can occupy a wider variety of orbits and host stars than previously recognized, and that the detailed birth mechanisms may depend on a balance between disk mass, temperature, and dynamic history. As researchers collect more transit data and refine disk models, the field moves toward a more unified view of planet formation that accommodates both core growth and gravitational fragmentation as complementary routes to giant planets.