News Excerpt:
More than four billion years ago, Venus had enough water to cover its surface with an ocean 3 km deep. Today, the planet only has enough for this ocean to be 3 cm deep.
More about News:
- Scientists have been able to account for a lot of the water Venus lost in this time but not all of it. Now, a team of scientists in the U.S. may have made a crucial advance.
- The team of scientists in the U.S. findings could plug a long-standing gap between the amount of water scientists expected Venus to have lost in the last 4.5 billion years and how much satellite observations say the planet has actually lost, which is a lot more.
Causes of Water loss:
- There are two reasons why Venus lost its water.
- The first is its hellish atmosphere as a result of its carbon dioxide-rich composition, which causes a strong greenhouse effect.
- The planet’s surface is hotter than water’s boiling point, simmering at 450 degrees C. So water can only exist as vapor in Venus’ atmosphere.
- Second, water was a victim of the planet’s proximity to the Sun.
- The Sun's heat and ultraviolet radiation broke water molecules into hydrogen and oxygen atoms in Venus's ionosphere, where charged particles move rapidly.
- The two theories broadly blame thermal and non-thermal processes for the water loss.
- The thermal process refers to hydrodynamic escape. As the Sun heated Venus’s outer atmosphere, it expanded, allowing hydrogen gas to leak to space. This escape lasted until the outer atmosphere sufficiently cooled, by about 2.5 billion years ago.
- Research focused on how water loss occurs in the present day, specifically via a non-thermal process.
- They focused on hydrogen atoms escaping Venus to space. Water levels drop as a result because the oxygen atoms left behind have fewer hydrogen atoms with which to form water.
Key Findings:
- HCO+ dissociative recombination reaction (DR) occurs at an altitude of about 125 km above the clouds of Venus, in the upper atmosphere.
- This reaction was found to accelerate the decline of water on Venus after the hydrodynamic escape of hydrogen gas ended.
- The HCO+ DR reaction could have doubled the rate at which Venus lost water through hydrogen escape.
- If Venus had oceans in the past, they could have lasted longer than expected due to the faster rate of hydrogen escape, which would have allowed more water to be lost in the same amount of time.
- According to the model, the amount of water on Venus would have stayed roughly the same from nearly 2 billion years ago until the period when the HCO+ DR reaction started influencing water loss..
Way Forward:
- Direct evidence of HCO+ ions and the HCO+ DR process in Venus's atmosphere is still lacking, and future missions are needed to confirm their presence and role in water loss.
- Understanding Venus's water loss could shed light on planetary habitability and whether Venus is abnormally dry or Earth is abnormally wet.
