Water is essential to life as we know it. Scientists are debating how it got to Earth and whether rocky exoplanets orbiting distant stars could be formed by the same processes. The new findings may come from the PDS 70 planetary system, located 370 light-years away. The star hosts both an inner disk and an outer disk of gas and dust, separated by a gap 5 billion miles wide (8 billion kilometers), and within this gap are the two known gas giant planets.
New measurements by NASA’s James Webb Space Telescope‘s MIRI (Mid-Infrared Instrument) detected water vapor in the system’s inner disk less than 100 million miles from the star a region where rocky terrestrial planets can form. (Earth orbits 93 million miles from our Sun.) This is the first detection of water in a terrestrial region of a disk already known to host two or more protoplanets.
James Webb Space Telescope’s MIRI detected water vapor
lead author Giulia Perotti of the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany Says “We’ve seen water in other disks, but not as close and in the system where the planets are currently gathering.” We couldn’t make this type of measurement before Webb”.
MPIA Director Thomas Henning, co-author of the paper says “This discovery is extremely exciting because it probes the region where rocky Earth-like planets typically form. Henning is co-principal investigator of Webb’s MIRI (Mid-Infrared Instrument), which performed the detection, and principal investigator of the MIRI Mid-Infrared Disk Survey (MINDS) program, which acquired the data”.
Steam environment for planet formation
PDS 70 is a K-type star, cooler than our Sun and estimated to be 5.4 million years old. This is relatively old for stars with planet-forming disks, which made the discovery of water vapor surprising.
Over time, the content of gas and dust in the disks forming the planets decreases. Either the central star’s radiation and winds blow away such material, or the dust grows into larger objects that eventually form planets. Because previous studies had failed to detect water in the central regions of similarly aged disks, astronomers thought it might not survive the harsh stellar radiation, resulting in a dry environment for any rocky planets to form.
Astronomers have not yet detected any planets forming in the inner disk of PDS 70. However, they see the raw materials for building rocky worlds in the form of silicates. The detection of water vapor means that if rocky planets form there, they will have water available from the start.
co-author Rens Waters of Radboud University in the Netherlands says “We find a relatively large number of small dust grains. Combined with our water vapor detection, the inner disk is a very exciting place”.
