Ultra-low-density exoplanets observed around a young star

In 1992, the first planet outside our Solar System was discovered¹. Since then, astronomers have catalogued thousands of such exoplanets, most of which are found in planetary systems that are very different to our own. The early stages of a planetary system’s evolution are pivotal in determining its structure, so observing exoplanets around young stars is crucial for understanding trends in the catalogue of mature exoplanets. Writing in Nature, Livingston et al.² present a detailed dynamical study of a young planetary system — the roughly 20-million-year-old star V1298 Tau and its four known orbiting planets. Using observations of small perturbations in the motions of the planets, the researchers identify them as large, low-density ‘super puff’ planets.