Why in the News?

Over four billion years ago, Venus had enough water to potentially cover its surface with an ocean approximately 3 km deep, but today, it would remain with only 3 cm.

• A research by US scientists explain the Non-Thermal Dissociative Recombination (DR) responsible for faster loss of water from Venus.

Water Loss on Venus:

• Venus lost its water primarily due to two factors:

• • • Evaporation due to Greenhouse Effect: Its dense atmosphere rich in carbon dioxide, creating a strong greenhouse effect and surface temperatures around 450 degrees Celsius, which prevents water from existing in liquid form.
    • Proximity to the Sun: This leads to the disintegration of water molecules into hydrogen and oxygen in the ionosphere under solar heat and ultraviolet radiation.

• Mechanism of Water Loss:

1. Thermal Process: Initially, hydrodynamic escape was significant, where solar heating caused the outer atmosphere to expand, allowing hydrogen to escape into space. This process cooled and slowed about 2.5 billion years ago.
2. Non-Thermal Process: Focus of recent study; involves hydrogen escaping into space, reducing water formation as oxygen atoms lack hydrogen to bond with.

Key Research Findings: Non-thermal Dissociative Recombination (DR)

The discrepancy in water loss rates was addressed by identifying a previously overlooked chemical reaction involving the formyl cation (HCO+).

• HCO+ dissociative recombination (DR) reaction occurs when HCO+ gains an electron and splits into CO and a hydrogen atom, which then escapes into space.
• This reaction is responsible for losing out water without evaporation.
• This reaction was modelled to significantly increase the rate of hydrogen escape, potentially doubling the rate at which Venus lost water.
• The model suggests that water levels on Venus would have been stable from nearly 2 billion years ago due to the ongoing non-thermal HCO+ DR reaction, yet some water remains today.

Future Research on Venus

• Existence of HCO+ Ions: Direct evidence of HCO+ ions in Venus’s atmosphere is still missing. Past missions did not focus on this molecule, and its involvement in water loss was not previously considered crucial.
• Future Missions: The findings underscore the importance of future Venus missions to investigate the presence of HCO+ in the upper atmosphere, similar to the MAVEN mission to Mars.

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