A breakthrough discovery may finally unravel the mystery behind Venus’s water loss, shedding light on how the once-habitable planet transformed into the arid wasteland we know today.
Venus, captured by NASA’s Magellan spacecraft. (Image credit: NASA/JPL) Scientists have pinpointed a water-loss mechanism on Venus, offering insight into the depletion of its once abundant water reservoirs. This newfound process, associated with a previously overlooked molecule high in Venus’s atmosphere, accelerated water escape at twice the rate previously estimated. The accelerated water loss suggests that Venus might have retained its oceans and potentially habitable conditions for a longer duration before succumbing to desiccation.
Eryn Cangi, a research scientist at the Laboratory for Atmospheric and Space Physics (LASP) in Colorado and co-author of the study, emphasized the implications, stating, “This would provide more time for possible life to arise.” However, she cautioned that definitive conclusions regarding the presence of oceans or life on Venus require further extensive research over many years.
Previous studies suggest that Venus and Earth received comparable amounts of water early in their history, primarily from water vapor-emitting volcanoes and icy comets. Estimates indicate that Venus once boasted enough moisture to submerge its surface under approximately 1.8 miles (3 kilometers) of water. However, Venus’s proximity to the Sun subjected it to intense solar radiation, leading to the gradual evaporation of its water reservoir through the dissociation of atmospheric water molecules into hydrogen and oxygen atoms. Subsequently, the lightweight hydrogen escaped into space via hydrodynamic escape, leaving Venus devoid of water.
While this process elucidates the bulk of Venus’s water loss within the initial billion years of its existence, it fails to account for the residual 330 feet (100 meters) of water likely left behind once hydrogen escape ceased.
The new study proposes a novel water loss mechanism dubbed HCO+ dissociative recombination (DR), wherein positively charged hydrogen, carbon, and oxygen atoms combine with negatively charged electrons to produce carbon monoxide (CO) and hydrogen. The liberated hydrogen then escapes into space. As water serves as the primary source of Venus’s hydrogen reservoir, this mechanism effectively dehydrates the planet. Computer simulations of reactions in Venus’s upper atmosphere validate this mechanism, bridging the gap between anticipated and observed water loss.
Lead author Michael Chaffin, a research scientist at LASP, likened the remaining water on Venus to a few droplets left in an emptied water bottle. While conventional water loss processes can’t account for this remnant, the swift removal of water from the atmosphere via DR explains Venus’s current dry and scorching conditions.
Published in the journal Nature, this study offers a crucial breakthrough in understanding Venus’s evolution and underscores the complex interplay of atmospheric processes shaping planetary climates.
