Young sunlike system reveals comets may carry water toward forming planets

Astronomers have discovered signs of exocomets, comets outside our solar system, circling a young star named PDS 70, located approximately 370 light-years away from Earth. These findings suggest that comets could play a crucial role in delivering water to the inner regions of a planetary system, where planets form. The research, led by Aline Novais of Lund University in Sweden, was published in Nature Communications and builds upon earlier detections of water vapor near the star dating back to 2023. The PDS 70 system is roughly 5 million years old, making it one of the youngest known systems where such comet activity has been observed. It contains at least two gas giant planets orbiting a star slightly cooler than the Sun. Observations made in 2018 revealed sodium gas moving at several kilometers per second relative to the star. This movement, appearing and disappearing over multiple nights, aligns with patterns expected from comets passing in front of the star. As comets approach their host stars, heat causes ice on their surfaces to turn directly into gas, leaving detectable imprints in the star’s light. Novais noted that this discovery marks the first time scientists have identified exocomets around a relatively cool star similar to the Sun. She emphasized that the system is the youngest in which such comet activity has been proposed, offering a rare glimpse into the early dynamics of a planetary system. To understand the potential paths of these comets, researchers conducted simulations showing how gravitational forces from the gas giants could influence objects in the outer reaches of the system. These forces might propel comets inward, bringing them closer to the star. Since comets originate in the colder outer regions, where water exists as ice, this process could transport water and other volatile materials to areas where planets form. Alexandra Stockwell Murphy, another astronomer at Lund University, highlighted the similarity to processes believed to have occurred in the early solar system. She suggested that comets may have played a role in delivering water to the young Earth, potentially explaining the presence of liquid water on our planet today. The origin of Earth’s water remains a topic of scientific debate. Two leading theories propose that water-rich asteroids or comets delivered it to Earth. The PDS 70 system offers a chance to observe a similar phenomenon during the early stages of planetary formation. With the upcoming launch of the Extremely Large Telescope in Chile, researchers anticipate gaining more insights into the system’s structure and the mechanisms behind the transportation of water and other planetary building blocks. Jens Hoeijmakers, an astronomy researcher at Lund University, mentioned that future studies using advanced telescopes could reveal additional planets within the PDS 70 system. Such discoveries would provide a clearer understanding of how water and essential elements for life are distributed throughout developing planetary systems. The findings from the PDS 70 system contribute significantly to ongoing efforts to unravel the mysteries of planetary formation and the origins of water on Earth. By observing these processes in action, scientists hope to refine models of how planets develop and how life-supporting conditions emerge in different parts of the galaxy.