Giant Planet’s Formation Caught in Action
Excerpt: Astronomers took a direct image of a massive protoplanet embedded in a protoplanetary disk. The system provides strong evidence for an as-yet-unconfirmed theory of planet formation. ...Jupiter-class gas giants on far-flung orbits have challenged what is known as the standard formation scenario. Scientists converged on the scenario that our solar system’s giant planets formed via accretion within the gaseous protoplanetary disk. Rocky planetary cores fed on pebbles or planetesimals, and once the cores reached a certain mass, they began gobbling up the surrounding gas, rapidly becoming giant planets. But that process works only when planets form relatively close to their host stars—the gas giants found on wide orbits would not have had time to grow a sufficiently massive core before the gaseous disk dissipated. The unstable disk model is one of several alternative models suggesting that a massive and gravitationally unstable protoplanetary disk could fragment into dense clumps, directly giving birth to wide-orbiting planets. ...Now, a team of scientists has made a discovery that might have been just the evidence the community has been waiting for. The team imaged a massive protoplanet orbiting the star AB Aurigae at about 93 times the distance between Earth and the Sun. Scientists caught the planet in an early stage of formation, still embedded in a protoplanetary disk. The properties of both the planet and the disk match well the predictions of the unstable disk model. The study was published in Nature Astronomy.…