NASA’s James Webb Space Telescope, the most powerful and complex space observatory ever built, has revealed a surprising discovery: rocky planets can form in the inner regions of a disk around a massive star, despite the intense radiation and strong stellar winds.
Massive stars, which are more than eight times the mass of the sun, are rare and short-lived, but they play a crucial role in the evolution of the universe. They produce heavy elements, such as iron and gold, and enrich the interstellar medium with their explosive deaths as supernovae. They also emit intense ultraviolet radiation and strong stellar winds, which can shape and ionize the surrounding gas and dust.
However, the effects of these extreme environments on the formation of planets around massive stars are poorly understood. Previous observations have shown that massive stars can host gas giant planets, such as Jupiter and Saturn, in their outer regions, but the fate of rocky planets, such as Earth and Mars, in their inner regions is unclear.
Using NASA’s James Webb Space Telescope, an international team of astronomers has provided the first observation of water and other molecules in the highly irradiated inner, rocky-planet-forming regions of a disk around a massive star. The disk, which is about 10,000 light-years away from Earth, belongs to a young star system called AFGL 4176, which consists of at least two massive stars and several smaller stars.
The team used Webb’s Near-Infrared Spectrograph (NIRSpec) instrument to obtain high-resolution spectra of the disk, which revealed the presence of water vapor, carbon monoxide, hydrogen cyanide, and acetylene. These molecules are the building blocks of life, and their detection indicates that the disk has enough material and chemistry to form rocky planets.
How rocky planets can survive in extreme environments
The team also used Webb’s Mid-Infrared Instrument (MIRI) to measure the temperature and the structure of the disk, which showed that the disk has a gap between the inner and the outer regions, similar to the asteroid belt in our solar system. The gap, which is about 10 astronomical units (AU) wide, is likely caused by the gravitational interaction between the massive stars and the disk.
The team found that the inner region of the disk, which extends from about 0.5 AU to 10 AU, is surprisingly warm and dense, despite being exposed to the harsh radiation and the stellar winds from the massive stars. The team estimated that the inner region contains about 20 Earth masses of dust, which is enough to form several rocky planets.
The team also found that the inner region is shielded from the radiation and the stellar winds by a layer of gas and dust above the disk, which acts like a protective umbrella. The layer, which is about 0.1 AU thick, absorbs most of the ultraviolet radiation and deflects most of the stellar winds, allowing the inner region to maintain a relatively stable and hospitable environment for planet formation.
The team concluded that rocky planets can form and survive in the inner regions of disks around massive stars, as long as the disks have enough material and shielding to withstand the extreme environments. The team also suggested that rocky planets around massive stars could have unique features, such as exotic atmospheres, strong magnetic fields, and diverse geology.
The implications and the future of the discovery
The discovery of rocky planets in extreme environments has important implications for the understanding of the diversity and the origin of planetary systems in the universe. It also challenges the conventional wisdom that rocky planets can only form and thrive around low-mass stars, such as the sun.
The team plans to use Webb to further study the disk around AFGL 4176, and to search for other disks and planets around massive stars. Webb, which was launched in December 2021, is a joint project of NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA). It is designed to observe the infrared universe, and to answer some of the most fundamental questions in astronomy and cosmology.
