Pristine ices in a planet-forming disk revealed by heavy water

TL;DR

This study provides evidence that water in planet-forming disks is inherited from earlier star formation stages, based on high deuteration ratios of water isotopologues observed in the V883 Ori disk.

Contribution

It demonstrates the inheritance of water ice in disks through isotopic analysis, linking early star formation to later planetary bodies.

Findings

High D$_2$O/H$_2$O ratio consistent with protostellar envelopes and comets.

Deuteration ratios indicate water is inherited, not reprocessed.

Water in disks originates from early star formation phases.

Abstract

Water is essential to our understanding of the planet-formation process and habitability on Earth. Although trace amounts of water are seen across all phases of star and planet formation, the bulk of the water reservoir often goes undetected, hiding crucial parts of its journey from giant molecular clouds to planets. This raises the question of whether water molecules in comets and (exo-)planets is largely inherited from the interstellar medium or if the water molecules are destroyed and then reformed in the disk. Water isotopologue ratios involving doubly deuterated water (D$_2$O) are a sensitive tracer to answer this question. We present strong evidence of inheritance through an enhancement of D$_2$O in the outbursting V883 Ori disk. The high D$_2$O/H$_2$O ratio of $(3.2 \pm 1.2) \times 10^{-5}$ is consistent with values seen in protostellar envelopes and a comet and is two orders of magnitude higher than expected if water is reprocessed. The high deuteration of the heaviest isotopologues D$_2$O/HDO = $(2.3 \pm 1.0) \times $HDO/H$_2$O further establishes the inheritance of water. We conclude that water ice in disks originates from the earliest phases of star formation, providing the missing link between cold dark clouds and (exo-)comets.