More than four billion years ago, Venus had enough water to cover its surface with an ocean 3 km deep. Today, however, the planet only possesses enough water for an ocean 3 cm deep. While scientists have managed to account for much of the water lost over time, a significant portion remains unaccounted for. A recent study conducted by a team of U.S. scientists may have made a crucial breakthrough in solving this enduring mystery.
Currently, Venus is 100,000 times drier than Earth, raising questions about this anomaly. Is it that Venus is abnormally dry, or is Earth unusually wet? The implications of this question are profound for understanding planetary habitability.
Scientists have identified two primary reasons for the drastic water loss on Venus:
The research team, led by Dr. Eryn Cangi, published their findings in Nature, emphasizing the importance of the formyl cation (HCO+), a positively charged molecule. Their study focused on the escape of hydrogen atoms from Venus into space, which directly reduces the availability of hydrogen needed to combine with oxygen to form water.
Their models indicated that a specific chemical reaction involving HCO+, known as dissociative recombination (DR), occurs at approximately 125 km above Venus’s surface. This reaction splits HCO+ into carbon monoxide (CO) and a hydrogen atom, which subsequently escapes into space. The researchers concluded that this process might have doubled the rate at which Venus lost its water.
This groundbreaking study suggests that if Venus once had oceans, they could have lasted longer than previously believed. The increased rate of hydrogen escape implies that more water could have been lost over time. Remarkably, the amount of water on Venus has remained relatively stable for nearly 2 billion years, as the non-thermal HCO+ DR process would have continued to drain the planet's water supply indefinitely.
Furthermore, comet impacts could have served as a possible means for Venus to replenish its water. However, it is important to note that there is currently no direct evidence for the presence of HCO+ ions in Venus’s atmosphere. Previous space missions did not specifically search for these ions, focusing instead on other atmospheric chemical reactions.
Future missions dedicated to investigating Venus's upper atmosphere, similar to NASA’s MAVEN mission to Mars, may provide the necessary evidence to confirm the existence of HCO+ ions.
Understanding whether Venus is abnormally dry or if Earth is unusually wet carries significant implications for planetary habitability. This research opens new avenues for exploring the history of water on Venus and enhances our understanding of planetary atmospheres. As scientists continue their investigation, they hope to unveil more about the enigmatic history of our neighboring planet.
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