How Does A Planet Form? Images from the Subaru and Hubble Space Telescopes Shed Light on the Process

An image of the protoplanet AB Aur b orbiting AB Aurigae (indicated by the star symbol). The size of Neptune’s orbit around our Sun is shown for scale. Over a 13-year span, AB Aur b has moved in a counterclockwise motion around its star. Credit: Thayne Currie/Subaru Telescope.

Over a 13-year span, images from the Subaru and Hubble Space Telescopes captured the initial growth stages of a Jupiter-like (gas giant) planet. The protoplanet, named AB Aur b, was photographed orbiting a two-million-year-old star, AB Aurigae. An international team led by Thayne Currie of the Subaru Telescope and Eureka Scientific produced the images using the Subaru Telescope’s extreme adaptive optics system (SCExAO), its infrared spectrograph (CHARIS), and its visible light camera (VAMPIRES), as well as Hubble’s Space Telescope Imaging Spectrograph (STIS) and its Near Infrared Camera and Multi-Object Spectrograph (NICMOS). Found to be nine times more massive than Jupiter, AB Aur b orbits its star at a distance of 8.6 billion miles, over three times the distance between the Sun and Neptune. These findings are inconsistent with a widely held hypothesis for giant planet formation.

The two leading hypotheses for the formation of Jupiter-like planets are core accretion and disk instability. Core accretion, the currently accepted model, posits that the rocky core of a planet forms via the slow coalescence of small solid objects (dust grains to boulders) with the surrounding gases, then being accreted rapidly. In contrast, the disk instability model suggests that Jupiter-like planets form directly due to local gravitational collapse in the protoplanetary disk. In the case of AB Aur b, the growth of such a massive and distant protoplanet cannot be explained by the core accretion model because solid cores are not expected to form at such large distances from their stars. Instead, the work by Currie and the team shows that Jupiter-like planets can form through disk instability. These results offer insight into the history of our own solar system and pave the way for further protoplanetary and exoplanetary research, aligning with the recent launch of the James Webb Space Telescope. READ MORE