A dramatic rise in the deuterium/hydrogen ratio was revealed in the Venusian atmosphere

Recent findings from Venus The EXPRESS mission reveals unexpected concentrations of water molecules in Venus’ atmosphere, suggesting it once had Earth-like water levels.

The study examines how solar radiation increased HDO/H₂O ratio provides insights into the climate history of Venus and its implications for planetary habitability.

Detecting Water Variations on Venus

Thanks to observations by the Solar Eclipse in the Infrared (SOIR) instrument on the European Space Agency’s (ESA) Venus Express spacecraft, researchers have detected an unexpected increase in the abundance of two water molecule variants – H₂O and HDO – and their ratio is HDO/H₂O. in the mesosphere of Venus. This phenomenon challenges our understanding of Venus’ water history and the possibility that it was habitable in the past.

Venus: Earth’s twin is a turn

Currently, Venus is a dry, hostile planet. Venus has a pressure nearly 100 times greater than Earth and a temperature of 460 °C (860 °F). Its atmosphere is covered by thick sulfuric clouds acid And water droplets, very dry. Most of the water is found below and within these cloud layers. However, Venus may have once supported water, similar to Earth.

„Venus is called Earth’s twin because of its similar size,” notes Tohoku University researcher Hiroki Karyu, adding that despite the similarities between the two planets, it has evolved differently. Unlike Earth, Venus has extreme surface conditions.

Unraveling Venus’ watery past

Examining the abundance of H₂O and its deuterated HTO (isotopolox) reveal insights into the water history of Venus. It is generally accepted that Venus and Earth initially had the same HDO/H₂O ratio. However, the ratio observed in the total atmosphere of Venus (below 70 km) is 120 times higher, indicating significant deuterium enrichment over time.

This enrichment is primarily due to solar radiation breaking the water isotopologues in the upper atmosphere, producing hydrogen (H) and deuterium (D) atoms. Since H atoms escape into space more easily due to their low mass, HDO/H₂O rate increases gradually.

Mechanisms of water variability in the Venusian atmosphere

To find out how much H and D escape into space, it is critical to measure water isotopologues at altitudes where sunlight can refract them, which occurs above clouds above ~70 km. The study found two surprising results: concentrations of H₂At 70 and 110 km altitude O and HDO increase, and HDO/H₂The O ratio rises significantly in this range, reaching 1500 times that of Earth’s oceans.

A mechanism proposed to explain these findings involves the behavior of hydrated sulfuric acid (H₂SO₄) aerosols. These aerosols form just above the clouds, where the temperature drops below the sulfur water dew point, leading to the formation of deuterium-enriched aerosols. These particles rise to higher altitudes, where increased temperatures vaporize them, releasing a significant fraction of HDO relative to H.₂O. The steam is then carried downstream, restarting the cycle.

Implications for planetary life

The study emphasizes two main points. First, variations in elevation play an important role in locating the D and H reservoirs. Second, increased HDO/H₂The O ratio ultimately increases the deuterium release, affecting the long-term evolution of the D/H ratio.

These findings encourage the incorporation of height-dependent processes into models to make more accurate predictions of D/H evolution. Understanding the evolution of life and water history on Venus will help us understand the factors that make a planet habitable, and thus help us know how to avoid Earth following in the footsteps of its twin.

These results are published Proceedings of the National Academy of Sciences On August 12, 2024.

Reference: „An Unexpected Increase in the Deuterium to Hydrogen Ratio in the Venus Mesosphere” Arnaud Mahieux, Sébastien Viscardi, Roger Vincent Yelle, Sarah Chamberlain, Severine Robert, Arianna Picchiali, Lovink Trompett, Justin Trompett, Epuric Trompett Nakagawa, Shungo Koyama, Romain Maggiolo, By Nuno Pereira, Gail Cessatur, Yannick Willem, and Ann Karin Vandel, 12 August 2024, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2401638121