天文学：新惑星の発見が宇宙の知識の空白を埋める

The detection of a new small gas giant planet by the James Web Space Telescope (JWST) is reported in Nature this week. The discovery helps to improve our understanding of early planet formation and the dynamical processes that take place in protoplanetary disks.

Planets are thought to form within protoplanetary disks — orbiting collections of dust and gas found around newly formed stars. Observations of such disks commonly see ring-like structures and gaps, which are thought to be signatures of unseen ‘shepherd’ planets; however, direct observations of the planets responsible for these features have proved elusive.

Anne-Marie Lagrange and colleagues used the JWST to search for such planets in the three-ringed disk around TWA 7, a star that formed approximately 6.4 million years ago. They detect a possible exoplanet with a mass smaller than Jupiter but larger than Neptune (commonly referred to as a sub-Jupiter). The candidate exoplanet, named TWA 7b, is estimated to be 0.3 times the mass of Jupiter and is orbiting 52 astronomical units (au; where 1 au is the average distance between the Earth and the Sun) from the star. These mass and orbital features match the expected properties of an exoplanet that could have formed in the gap between the first and second ring of the disk.

This imaging provides new insights into the interactions between protoplanetary disks and surrounding objects, as well as expands the use of imaging to learn more about small exoplanets.