Venus shares many similarities with Earth - similar in size, density, and rocky composition.
However, as we know, Venus boasts an environment entirely inhospitable to life: with an average surface temperature of 465°C.
Despite its harsh conditions, there has long been speculation about the presence of liquid water on Venus's surface. Scientists from the University of Colorado Boulder now believe they have identified the reason behind Venus's water loss. Recently published in Nature, their research utilized computer models to simulate the behavior of hydrogen in Venus's atmosphere.
Illustration of Venus. Image Source: NASA
Hydrogen atoms can be found in the upper atmosphere of Venus combined with carbon and oxygen, forming "formyl cation" (HCO+), which is an effective product of water and carbon dioxide.
HCO+ contains hydrogen, carbon, and oxygen atoms and can be found in interstellar molecular clouds and planetary atmospheres. It can be formed through several chemical reactions, including those related to water.
In the atmosphere of Venus, these cations can combine with free electrons, causing HCO+ to split into hydrogen atoms and carbon monoxide molecules.
The study's lead authors, Michael Chaffin and Eryn Cangi from the Laboratory for Atmospheric and Space Physics at the University of Colorado Boulder, previously theorized the ability of hydrogen to escape the atmosphere when analyzing Mars' history. They suggest that dissociative recombination in the upper atmosphere of Venus leads to hydrogen loss into space, depriving the planet of one of the elements necessary for water formation.
Hydrogen escape is also a potential consequence of significant changes in Earth's atmospheric behavior nearly 600 million years ago.
Imaginary illustration of hydrogen escape. Image source: University of Colorado Boulder.
Chaffin stated, "Despite Venus being similar in size and mass to Earth, its water resources are 100,000 times less than Earth's."
However, if understanding the behavior of HCO+ in the atmosphere is key to understanding water on Venus, then Chaffin and Cangi face a major obstacle.
While their analysis suggests that the global-scale aridity on Venus can only be explained by the presence of abundant HCO+ in the atmosphere, several probes that have explored Venus have never measured this molecule.
"HCO+ should actually be one of the most abundant ions in the Venusian atmosphere," Chaffin said. Their analysis indicates that the global-scale aridity on Venus can only be explained by the presence of abundant HCO+ in the atmosphere, but due to the lack of instruments on previous missions to Venus capable of measuring HCO+, the team at the University of Colorado Boulder hopes that new missions can help confirm their theory.
NASA's DAVINCI mission is set to launch in 2029, specifically to analyze the chemical composition of Venus' atmosphere. By 2031, this 1-meter-wide probe will enter the thick clouds of Venus, where it will measure the gases present and capture images of the planet's surface.
Related paper information: https://doi.org/10.1038/s41586-024-07261-y
