Image: © NAVCAM/Rosetta/ESA
Comets are often regarded as reservoirs of material preserved from the early Solar System, offering a unique opportunity to explore its history. In August 2014, the Rosetta spacecraft, part of a mission launched and operated by the European Space Agency (ESA), rendezvoused with Jupiter-Family Comet (JFC) 67P/Churyumov-Gerasimenko (67P) at a distance of approximately 3.6 AU.
Through detailed observations, Rosetta uncovered a wealth of information about the comet’s gas and dust composition. One of its key findings was the measurement of the D/H ratio in water from 67P, which initially indicated one of the highest ratios ever observed—more than three times the terrestrial value. This suggested that JFCs formed at significant distances from the Sun and are not the primary source of Earth’s water.
However, this new study challenge this interpretation, arguing that the measured values might not reflect the comet’s bulk composition. Instead, the authors point to the impact of sublimation processes and localized interactions between dust and gas in the comet’s coma, which can modify D/H measurements. These results reveal a surprising variability in cometary isotopic compositions, questioning the long-standing assumption of uniform deuterium enrichment in comets.
This new perspective hints at a closer connection between JFCs and the inner Solar System, potentially reshaping our understanding of water distribution in the early Solar System and its role in the origin of Earth’s water.
Source paper: https://www.science.org/doi/10.1126/sciadv.adp2191