PDS 70, a star slightly cooler than the Sun some 370 light years from Earth, is just over five million years old and already hosts at least two gas giants, making it one of astronomy's favourite laboratories for planet formation. Water vapour was detected near the star in 2023, raising the question of how volatile material travels from a system's frozen outer reaches to the warm inner zone where rocky planets assemble.
Analysing observations from 2018, a team led by Aline Novais, a postdoctoral researcher in Lund University's Department of Physics, found sodium gas moving at several kilometres per second relative to the star, appearing and disappearing over several nights. That transient pattern matches what would be expected if comets were passing in front of the star, their surface ices sublimating directly into gas. Orbital simulations showed that the system's gas giants can fling distant icy bodies inward. The study appears in Nature Communications.
The result is the first evidence of exocomets around a relatively cool, Sun-like star, and PDS 70 is the youngest system in which exocomet activity has been proposed. For scientists puzzling over how the young Earth acquired its oceans, a directly observed delivery mechanism in another system is a valuable analogue. The Extremely Large Telescope, under construction in Chile, should reveal whether additional planets lurk in the system and clarify how its building materials circulate.