Earth’s surface water is a defining feature that sets our planet apart within the Solar System, yet the source of this water remains a topic of scientific inquiry. Recent research published in Nature Communications explores this question by examining the distant solar system surrounding the young star PDS 70, located approximately 370 light-years away.
Investigating PDS 70
PDS 70 is a T-Tauri star that is only about 5.5 million years old, still in the process of evolving toward the main sequence. The system is notable for its two directly imaged exoplanets, PDS 70b and PDS 70c, captured by the ESO’s Very Large Telescope in 2018 and 2019. Observations from the James Webb Space Telescope (JWST) have detected water in the inner disk of this system, although the origins of this water remain unclear.
Research Findings
The study, led by post-doctoral researcher Aline Novais from Lund University, utilized archival data from the High Accuracy Radial velocity Planet Searcher (HARPS) to investigate the spectral lines of sodium in PDS 70. The researchers discovered variable absorption lines of neutral sodium that fluctuate daily in amplitude, number, and radial velocity. These lines are not uniformly distributed, indicating a clumpy presence of gas rather than a stable disk wind.
The variability of the gas, which appears and disappears over several nights and moves faster than the star itself, supports the hypothesis that these lines are produced by sublimating exocomets passing in front of PDS 70. The team suggests that the sodium observed may originate from the sublimation of planetesimals on highly elliptical orbits, akin to exocomets observed in other systems.
Implications for Water Delivery
Novais stated, “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.” This finding marks the first evidence of exocomets around a relatively cool star similar to our Sun and highlights the potential for water delivery mechanisms in young planetary systems.
While the exocomet hypothesis is favored, the researchers acknowledge that a disk wind could still account for the observed spectral lines. They note that uncertainties in model parameters, such as the star’s mass loss rate, complicate definitive conclusions. Further observations will be necessary to confirm exocomet activity in PDS 70.
Co-author Jens Hoeijmakers emphasized the importance of future observations, particularly with the upcoming Extremely Large Telescope in Chile, which could provide more insights into the system’s dynamics and the transport of water and other essential building blocks for planet formation.
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