Free Astronomy Magazine January-February 2026

33 JANUARY-FEBRUARY 2026 ing the journey of water through planet formation, and how this water made its way to our Solar Sys- tem, and possibly Earth, through similar processes.” Does this mean that the water in your morning cup of coffee could be older than the Sun? The chemical fingerprinting of D ₂ O shows that these water mole- cules have survived the violent processes of star and planet forma- tion, travelling billions of kilometers through space and time before, ending up in planetary systems like our own. Instead of being destroyed and reformed in the disk, the bulk of this water is inherited from the earliest, coldest stages of star forma- tion, a cosmic hand-me-down that may also be present on Earth today. “ Until now, we weren’t sure if most of the water in comets and planets formed fresh in young disks like V883 Ori, or if it’s ‘pristine,’ origi- nating from ancient interstellar clouds,” shares John Tobin, a scien- tist with the U.S. National Science Foundation National Radio Astron- omy Observatory, and second au- thor on this new paper. The detection of heavy water, using sensitive isotopologue ratios (D ₂ O/ H ₂ O), proves the water’s ancient heritage and provides a missing link between clouds, disks, comets, and ultimately planets. This finding is the first direct evidence of water’s interstellar journey from clouds to the materials that form planetary systems—unchanged and intact. Water is fundamental to life and habitability. Knowing where plane- tary water comes from helps us un- derstand the ingredients for life in our Solar System and in others. This discovery suggests that many young planets, and maybe even worlds be- yond our own, could inherit water billions of years older than them- selves, reminding us how deeply in- terconnected our existence is with the universe’s ancient past. insights into the history of water in our Solar System. Astronomers using the Atacama Large Millimeter/ sub- millimeter Array (ALMA) have made a first-ever detection of doubly deuterated water (D ₂ O, or “heavy water”) in a planet-forming disk around V883 Ori, a young star. This means that the water in this disk, and by extension the water in com- ets that form here, predates the birth of the star itself, having jour- neyed through space from ancient molecular clouds long before this solar system formed. “Our detection indisputably demonstrates that the water seen in this planet-forming disk must be older than the central star and formed at the earliest stages of star and planet forma- tion,” shares Margot Leemker, lead author on this paper, and a postdoc with the Department of Physics, Uni- versity of Milan. “This presents a major breakthrough in understand- A LMA’s image of the planet-form- ing disk around V883 Orionis. [ALMA (ESO/NAOJ/NRAO)/L. Cieza] !