This young planetary system, known as PDS 70, is located 370 light-years away from us. Its central star is approximately 5.4 million years old and colder than the Sun, surrounded by giant gas planets. Recent studies have identified one of these planets, PDS-70b, likely sharing an orbit with a third “sister” planet still forming in the system.
.jpg)
Simulation of the PDS 70 planetary system and its gas and dust disk. Image: NASA.
Different gas and dust disks – the necessary ingredients for both star and planet formation – surround the central star. The inner and outer disks are separated by 8 billion kilometers. Giant gas planets orbit within this range.
The James Webb Space Telescope detected signs of water vapor in the inner disk, situated less than 160 million kilometers away from the central star. Astronomers believe that this inner disk is where small rocky planets, similar to the planets in our Solar System, form if PDS 70 resembles the Sun. In our planetary system, Earth is located approximately 150 million kilometers from the Sun. The findings were published in the journal Nature.
“We have previously observed water in other gas and dust disks, but not to this extent and not in a system where planets are gathering. We couldn’t have made these measurements before the James Webb Space Telescope,” said Giulia Perotti, lead author and researcher at the Max Planck Institute for Astronomy in Heidelberg, Germany.
Astronomers were surprised to find water vapor near the star of the PDS 70 planetary system given its age. PDS 70 is relatively mature, with a star hosting a planet-forming disk. The gas and dust content in these disks gradually decreases over time due to the activity of the central star or matter coming together to form planets. Water had not been discovered in a planetary-forming disk of this age before, leading astronomers to believe that water cannot exist for such extended periods and any rocky planets here would be dry.
Currently, no planets have been found forming in the inner disk, but all the necessary ingredients for their formation have been detected. The presence of water vapor indicates that planets may contain water in some form. Time will tell if these planets form and if they have the potential for life.
“We found a significant amount of small dust particles. Combined with the water vapor discovery, the inner disk is an intriguing place,” said Rens Waters, co-author and astronomy professor at Radboud University in the Netherlands.
But where does the water vapor come from?
It is possible that hydrogen and oxygen atoms have combined to form water molecules in the inner disk, or that ice molecules are moving from the colder outer disk to the warmer inner disk, turning ice into water vapor.
Water vapor can remain stable despite its proximity to the central star, as layers of dust shield it from being destroyed by the star’s ultraviolet rays. The research team plans to observe this planetary system more closely with the James Webb Space Telescope in the future to unravel the mysteries of planet formation in this system.
“This discovery is extremely exciting as it explores an area where rocky planets like Earth are forming,” said Thomas Henning, co-author and director at the Max Planck Institute for Astronomy.