Despite its Earth-like size and source material, Venus is extremely dry, indicating near-total water loss to space. Using computer simulations, planetary scientists from the University of Colorado, Boulder and the Laboratory for Atmospheric and Space Physics at the University of Arizona, Tucson found that hydrogen atoms in the planet’s atmosphere go whizzing into space through a process known as dissociative recombination — causing Venus to lose roughly twice as much water every day compared to previous estimates.
Venus today is dry thanks to water loss to space as atomic hydrogen. Image credit: Aurore Simonnet / Laboratory for Atmospheric and Space Physics / University of Colorado at Boulder.
Despite being a close neighbor and being similar in size and source material to Earth, Venus is extremely dry.
Research has suggested that water from Venus’ once steam-dominant atmosphere was lost to space via a mechanism called hydrodynamic outflow.
However, this mechanism cannot remove all the water needed to explain current conditions, and other studied escape mechanisms are too slow to complete the process of water removal.
“Water is really important for life,” said Dr. Eryn Cangi, a researcher with the Laboratory for Atmospheric and Space Physics at the University of Arizona, Tucson.
“We need to understand the conditions that support liquid water in the universe, and that may have produced the very dry state of Venus today.”
“Venus is positively parched. If you took all the water on Earth and spread it over the planet like jam on toast, you’d get a liquid layer roughly 3 km (1.9 miles) deep.”
“If you did the same thing on Venus, where all the water is trapped in the air, you’d wind up with only 3 cm (1.2 inches), barely enough to get your toes wet.”
“Venus has 100,000 times less water than the Earth, even though it’s basically the same size and mass,” added Dr. Michael Chaffin, a researcher with the Laboratory for Atmospheric and Space Physics at the University of Arizona, Tucson.
The study authors propose a new explanation: a reaction called HCO+ dissociative recombination, which produces more escaping hydrogen than previously suggested processes.
HCO+ dissociative recombination would nearly double the rate of water loss to space from Venus and would resolve longstanding difficulties in explaining measured water abundances and isotope ratios on Venus.
Future Venus spacecraft missions need to measure HCO+ abundances to determine if HCO+ dissociative recombination is indeed the dominant mechanism for water loss.
“Our findings reveal new hints about why Venus, which probably once looked almost identical to Earth, is all but unrecognizable today,” Dr. Cangi said.
“We’re trying to figure out what little changes occurred on each planet to drive them into these vastly different states.”
The results appear in the journal Nature.
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M.S. Chaffin et al. Venus water loss is dominated by HCO+ dissociative recombination. Nature, published online May 6, 2024; doi: 10.1038/s41586-024-07261-y
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