Discovery on the planet Venus

Although nicknamed Earth's twin due to its similar size, Venus today presents very different surface conditions to those of our planet, with surface pressure almost 100 times higher and temperatures approaching 460°C. Venus is entirely covered by thick clouds of sulphuric acid and water droplets at altitudes of between 45 km and 65 km. What's more, its atmosphere is over 100,000 times drier than Earth's, and most of the water lies beneath the surface and within these cloud layers.

Thanks to observations made by the SOIR (Solar Occultation in the Infrared) instrument on board the European Space Agency's (ESA) Venus Express space probe, researchers at the Royal Belgian Institute for Space Aeronomy have revealed an unexpected increase in the abundance of two variants of water molecules – H2O and HDO – as well as their HDO/H2O ratio, in Venus' mesosphere.

This study highlights two important points. Firstly, a thorough understanding of any variations with altitude is essential for locating deuterium and hydrogen reservoirs in Venus' atmosphere, which will allow scientists to better understand the planet's water history. Secondly, an increase in the HDO/H₂O isotope ratio has an impact on the escape rates into space of hydrogen and deuterium.

This discovery provides a better understanding of the evolution of the planet Venus, allowing researchers to ascertain whether it has ever been habitable in the past.