An international team of scientists has conducted a study of the amount of deuterium in the atmosphere of Venus using the Solar Occultation Infrared instrument on the European Space Agency’s Venus Express probe. The data obtained made it possible to build a model of the planet’s water cycle mechanism and showed the importance of including altitude-dependent processes in the model for accurate predictions of the evolution of the deuterium/hydrogen ratio.

Today, Venus is a dry and hostile world. The pressure on it is almost 100 times greater than that of Earth, and the surface temperature is about 460°C. The planet’s atmosphere is extremely dry and is hidden under clouds of sulfuric acid and water droplets. Most of the water is under and within these cloud layers. However, Venus may once have been similar to Earth in the prevalence of water.

Studying semiheavy and normal water on Venus is helping scientists reconstruct its water history. Semiheavy water has the same chemical formula as normal water, deuterium hydroxide, H₂It is, but instead of two atoms of protium, the most common isotope of hydrogen with an atomic mass of one, oxygen is combined with a hydrogen atom and a deuterium atom D, a heavier isotope of hydrogen. A deuterium atom has an extra neutron in one nucleus, an atomic mass of two, and is called semi-heavy water HDO.

HDO/H ratio₂The O in the primary atmosphere of Venus is 120 times greater than that of Earth, indicating significant deuterium enrichment over time. This fact may indicate the presence of large amounts of moisture on the surface of Venus in the past. The planet’s dryness is primarily due to solar radiation destroying both types of water in the upper atmosphere, creating hydrogen (H) and deuterium (D) atoms.

Since H atoms are extremely light, they are not trapped in the atmosphere and do not fly into space, and the HDO/H2O ratio _gradually To determine how much H and D evaporate, researchers measure the amount of water species at altitudes where sunlight can destroy them. Quantification is achieved in the mesosphere at altitudes greater than 70 kilometers above the clouds.

When measuring with a probe Venus Express The researchers discovered two unexpected patterns: H concentrations ₂ O and HDO increase with altitude at the 70-110 km level and the HDO/H ratio ₂ It reaches an order of magnitude higher, reaching indicators 1500 times higher than terrestrial ones.

Large amounts of deuterium may explain the behavior of hydrated sulfuric acid (H) aerosols.₂FOR THIS REASON₄), is formed in the region at temperatures below the dew point of sulfur water. Such an environment leads to the formation of aerosols with the participation of deuterium, which is already in the cold region. Escaping particles rise to the height, where high temperatures cause their evaporation, and a larger fraction of HDO is released compared to H.₂O. The steam is then transported back to relatively cooler conditions, starting the cycle over again.

The researchers described two results as the most important. First, changes in altitude play a crucial role in determining the location of deuterium and hydrogen reserves. Second, the increasing HDO/H ratio₂As a result, O increases deuterium emission. These results indicate that it is necessary to include altitude-dependent processes in the model for accurate predictions of changes in the D/H ratio in the Venusian atmosphere.

Understanding the evolution of Venus’s natural conditions and the history of its water will help us understand what makes the planet habitable. This knowledge will help us prevent Earth from being reborn as an uninhabitable Venus. The study was published in the publication Proceedings of the National Academy of Sciences.