First Detection of Semi-Heavy Water Ice Around Young Sunlike Star

In a groundbreaking discovery, a team of astronomers led by researchers from Leiden University in the Netherlands and the National Radio Astronomy Observatory (NRAO) in Virginia, USA, has detected semi-heavy water ice (HDO) around the young sunlike protostar L1527 IRS. This detection marks the first time such ice has been robustly identified in the vicinity of a star, underscoring the potential origins of water in our solar system as predating the formation of the sun and its planets. The findings were published in *The Astrophysical Journal Letters* on June 16, 2025.

The research team utilized the James Webb Space Telescope (JWST) to ascertain the water deuteration ratio, a critical factor in understanding the origins of water. The deuteration ratio refers to the proportion of water molecules that contain deuterium, an isotope of hydrogen, instead of regular hydrogen. This ratio provides insight into the environmental conditions under which the water was formed. According to Dr. Katie Slavicinska, a Ph.D. student at Leiden University and lead author of the study, "Now, with the unprecedented sensitivity of Webb, we observe a beautifully clear semi-heavy water ice signature toward a protostar."

L1527 IRS, located approximately 460 light-years from Earth in the constellation of Taurus, exhibits a deuteration ratio that is strikingly similar to the ratios found in certain comets and the protoplanetary disks of more evolved young stars. Dr. John Tobin, an astronomer at NRAO and co-leader of the project, stated, "In several ways, it is similar to what we think our sun was when it began to form."

The presence of semi-heavy water ice is significant as it suggests that the water in our solar system may have originated from ancient, cold environments known as dark clouds, which are rich in dust, ice, and gas. This finding aligns with the hypothesis that a substantial portion of the water within our solar system was formed in these primordial conditions before the birth of the sun.

Dr. Ewine van Dishoeck, a professor of astronomy at Leiden University and co-author of the study, emphasized that this discovery adds to the accumulating evidence that the bulk of water ice remains largely unchanged throughout various stages of star formation. She noted, "This finding adds to the mounting evidence that the bulk of water ice makes its journey largely unchanged from the earliest to the latest stages of star formation."

Despite these promising results, the measured water ice deuteration ratio in L1527 IRS is slightly higher than those observed in some comets and on Earth. This discrepancy may arise from several factors, including potential chemical alterations that occurred during the water's journey through the protoplanetary disk or differences in the initial dark clouds that formed these celestial bodies.

To further investigate the origins and characteristics of semi-heavy water ice, Slavicinska and Professor Tom Megeath from the University of Toledo plan to expand their research efforts. They aim to analyze 30 additional protostars and primitive dark clouds using JWST, while Dr. Tobin continues to lead complementary observations with the Atacama Large Millimeter/submillimeter Array.

The implications of this research extend beyond academic curiosity; understanding the origins of water is crucial for comprehending the potential for life elsewhere in the universe. As scientists continue to unravel the complexities of star formation and the chemical processes that occur in these formative stages, the quest to trace the journey of water from dark clouds to planets remains a pivotal area of inquiry in astrophysics.

In conclusion, the detection of semi-heavy water ice around L1527 IRS not only strengthens the case for pre-solar water formation but also opens up new avenues for research into the origins of water in our solar system and beyond. Future investigations promise to shed light on the chemical evolution of water in various astrophysical environments, further enhancing our understanding of the universe's history and the potential for life beyond Earth.