Water is essential to life as we know it. However, scientists are debating how it got to Earth and whether the same processes could form rocky exoplanets orbiting distant stars. The new findings may come from the PDS 70 planetary system, located 370 light-years away. These observations were taken as part of the Guaranteed Time Observation 1282 program. This finding was published in the journal Nature.
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 (160 million kilometers) from the star — a region where rocky terrestrial planets can occur. to 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.
lead author Giulia Perotti of the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany said “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, discovery is extremely exciting because it probes the region where rocky Earth-like planets typically form”.
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. Since previous studies had failed to detect water in the central regions of similarly old 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.
“We find a relatively large number of small dust grains. Combined with our water vapor detection, the inner disk is a very exciting place,” said co-author Rens Waters of Radboud University in the Netherlands.
What is the origin of water?
The discovery raises the question of where the water came from. The MINDS team considered two different scenarios to explain their finding.
One possibility is that water molecules form where we detect them when hydrogen and oxygen atoms combine. The second possibility is that ice-covered dust particles are transported from the cool outer disk to the hot inner disk, where the water ice sublimates and turns into vapor. Such a transport system would be surprising because the dust would have to cross the large gap carved out by the two giant planets.
Another question raised by the discovery is how water could survive so close to the star when the star’s ultraviolet light should break up water molecules. Most likely, surrounding material such as dust and other water molecules act as a protective shield. As a result, the water detected in the PDS 70’s inner disk could have survived the destruction.
Finally, the team will use Webb’s two other instruments, NIRCam (Near-Infrared Camera) and NIRSpec (Near-Infrared Spectrograph) to study the PDS 70 system in an effort to gain an even better understanding.
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