Icy Exocomets Around a Distant Star Help Explain Earth's Water

A study published in Nature Communications suggests that the water detected in the inner disk of the young star PDS 70 may come from sublimation of icy planetesimals, rather than from a disk wind. The researchers found variable absorption lines of neutral sodium in archival HARPS spectra of PDS 70, which vary on a daily basis and are not uniform, indicating the presence of fast-moving gas. These lines are likely caused by comets passing in front of the star, sublimating off them and creating the observed spectral features. The study supports the exocomet hypothesis, suggesting that comets may have transported water to the inner parts of the planetary system, similar to how comets delivered water to Earth in the early Solar System. The researchers also modelled the orbits of exocomets in the PDS 70 system, finding that gas giants could perturb icy objects and bring them toward the star, a process similar to one that may have occurred in our Solar System. The findings suggest that exocomets orbiting a relatively cool star could be responsible for delivering water to the inner regions of planetary systems. The study highlights the importance of understanding the sources of Earth's water and how water is transported in planetary systems. The debate over the origin of Earth's water is similar to the 'nature vs. nurture' debate in human development, and the findings suggest that both mechanisms may contribute to the water content of a planet. The study concludes that more observations are needed to confirm exocomet activity in PDS 70 and to better understand how water is transported in planetary systems.

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