An international team of astronomers has used the NASA/ESA/CSA James Webb Space Telescope to make the first observation of water and other molecules in the inner disk regions that form rocky planets, in one of the most extreme environments in our galaxy.
These results suggest that the conditions for the formation of rocky planets typically found in disks in regions where low-mass stars form may also occur in regions where massive stars form, and perhaps in a wider range of environments, the European Space Agency reports in The Astrophysical Journal.
These are the first results from NASA’s James Webb Space Telescope’s eXtreme UV Environments (XUE) program, which focuses on characterizing planet formation disks in regions where massive stars form. These regions likely represent the environments in which most planetary systems formed. Understanding the influence of environment on planet formation is important for scientists to gain insight into the diversity of exoplanet populations observed.
Artist’s impression of a protoplanetary disk. ESA
The XUE program is targeting a total of 15 disks in three regions of the Lobster Nebula (also known as NGC 6357), a large emission nebula about 5,500 light-years from Earth in the constellation Scorpius. The Lobster Nebula is one of the youngest and closest star-forming regions, containing some of the most massive stars in our galaxy. Massive stars are hotter and therefore emit more ultraviolet (UV) radiation. This can disperse the gas in the disk, giving them an expected lifetime of just a million years. Thanks to Webb, astronomers can now study the effects of UV radiation on the inner regions of rocky planet-forming protoplanetary disks around stars like our Sun.
“Webb is the only telescope with the spatial resolution and sensitivity needed to study planet formation disks in regions where massive stars are forming,” said team leader Maria Claudia Ramirez-Tannus of the Max Planck Institute for Astronomy in Germany.
Astronomers aim to characterize the physical properties and chemical composition of rocky planet-forming disk regions in the Lobster Nebula using the Webb Medium Resolution Spectrometer (MRS) on the Mid-Infrared Imager (MIRI). This first result focuses on a protoplanetary disk called XUE 1, which resides in the star cluster Pismis 24.
Protoplanetary disk XUE 1 (MIRI emission spectrum: 13.3–15.5 μm). ESA
“Only the wavelength range and spectral resolution of MIRI allow us to probe the molecular composition and physical conditions of the warm gas and dust where rocky planets form,” said team member Arjan Bik of Stockholm University in Sweden.
Because of its location near several massive stars in NGC6357, scientists expect that XUE 1 has been exposed to intense ultraviolet radiation throughout its life. However, in this extreme environment, the team still found a number of molecules that are the building blocks of rocky planets.
“We found that the inner disk around XUE 1 is remarkably similar to those found in nearby star-forming regions,” said team member Rens Waters of Radboud University in the Netherlands. “We detected water and other molecules such as carbon monoxide, carbon dioxide, hydrogen cyanide and acetylene. However, the detected emission was weaker than some models predicted. This may indicate a small radius for the outer disk.”
“We were surprised and excited because this is the first time that these molecules have been detected in such extreme conditions,” added Lars Kuipers from Radboud University. The team also found evidence of small, partly crystalline silicate dust grains on the surface of the disk. These are thought to be the building blocks of rocky planets.
Protoplanetary disk XUE 1 (MIRI emission spectrum: 4.95–5.15 μm). ESA
These results are good news for the field of rocky planet formation, as the team found that conditions in the inner disk resemble those found in well-studied disks located in nearby star-forming regions where only low-mass stars form. This suggests that rocky planets can form in a much wider range of environments than previously thought.
The group notes that the remaining observations from the XUE programme are critical to establishing the commonality of these conditions.
“XUE1 shows us that the conditions for rocky planet formation exist, so the next step is to test how common this is,” says Ramirez-Tannus. “We’ll be looking at other disks in the same region to determine the frequency with which these conditions can be observed.”
Webb is the largest and most powerful telescope ever launched into space. Under an international cooperation agreement, ESA provided the launch service for the telescope using the Ariane 5 launch vehicle. Working with partners, ESA was responsible for the development and qualification of the Ariane 5 adaptations for the Webb mission and for the procurement of launch services by Arianespace. ESA also provided the workhorse NIRSpec spectrograph and 50% of the MIRI mid-infrared instrument, which was designed and built by a consortium of nationally funded European institutes (the MIRI European Consortium) in partnership with JPL and the University of Arizona. Webb is an international partnership between NASA, ESA and the Canadian Space Agency (CSA).
