This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: 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 5 million years old and lies about 370 light-years from Earth. The system has at least two gas giants orbiting a star that is slightly cooler than the sun. Water vapor 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 and first author of the study published in Nature Communications. The researchers analyzed observations from 2018 and detected sodium gas moving at several kilometers per second relative to the star.
The gas appears and disappears over 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," Novais says. 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 toward 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 channeled inward, they can transport water and other volatile substances to the region where planets form.
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