Astronomers at Lund University in Sweden have found evidence of exocomets – comets in other solar systems – orbiting a young star similar to our Sun. The observations point to a possible mechanism for how water might be transported from the cold outer regions of the planetary system to regions where planets form.
The PDS 70 planetary system is just over five million years old and lies around 370 light-years from Earth. The system has at least two gas giants and orbits a star that is slightly cooler than the Sun. Water vapour was detected near the star as early as 2023. Researchers in Lund have now shown that variations in sodium gas in front of the star may be a sign of comets passing through the inner parts of the system.
“Our study suggests that comets may be responsible for transporting water to the inner parts of the planetary system, where planets can form, in the same way as in the early Solar System,” says Aline Novais, an astronomy researcher at Lund University.
The researchers have analysed observations from 2018 and detected sodium gas moving at several kilometres per second relative to the star. The gas appears and disappears over the course of several nights – a pattern consistent with what one would expect when comets pass in front of a star. When a comet approaches its star, it heats up and the ice on its surface turns directly into gas – a process known as sublimation. The gas can then leave a measurable imprint in the star’s light.
“This is the first time we have seen evidence of exocomets orbiting a star that is relatively cool, much like our Sun. Furthermore, this system is the youngest in which exocomet activity has been proposed,” says Aline Novais.
The researchers have also simulated the comets’ orbits. The results show that objects far out in the planetary system can be affected by the gravitational pull of the gas giants and flung towards the star. This is particularly interesting because comets form in the cold outer regions of the planetary system, where water may exist as ice. If they are then channelled inwards, they can transport water and other volatile substances to the region where planets form.
“It is reminiscent of a possible process in the early Solar System, in which comets may have helped to deliver water to the young Earth,” says Alexandra Stockwell Murphy, an astronomer at Lund University.
Where the Earth’s water originally came from remains an open question. Water-rich asteroids and comets are two possible sources. PDS 70 gives researchers the opportunity to study a similar process whilst a planetary system is still in its early stages of development.
“And when the Extremely Large Telescope, which is currently being built in Chile, becomes operational in the coming years, we will be able to find out whether there are any further planets in the system and thus gain an even clearer picture of how water and other building blocks of planets are transported,” concludes Jens Hoeijmakers, an astronomy researcher at Lund University.
Journal: Nature Communications
DOI: 10.1038/s41467-026-76880-y
Article Title: Potential sublimating exocomets around the young star PDS 70
Publication Date: 24-Aug-2026
Institution: Lund University
Source: EurekAlert | Featured image credit: ALMA (ESO/NAOJ/NRAO)/A. Ribas et al.