Recent findings from the Venus Express mission have uncovered unexpected levels of water molecules in Venus' atmosphere, hinting at a potentially watery past similar to Earth. The study's focus on the HDO/H2O ratio sheds light on how solar radiation has influenced Venus' climatic history and the implications for its habitability. Observations by the Solar Occultation in the Infrared (SOIR) instrument on the Venus Express probe revealed elevated concentrations of H2O and HDO isotopologues in Venus' mesosphere. This discovery challenges previous notions about Venus and suggests it may have been habitable in the past. Despite being known as Earth's twin due to its size, Venus has evolved differently, with extreme surface conditions including high pressures and temperatures. The research highlights the importance of understanding the water isotopologues on Venus to unravel its watery past. The study found that the HDO/H2O ratio in Venus' atmosphere is significantly higher than initially believed, indicating substantial deuterium enrichment over time due to solar radiation breaking down water molecules into hydrogen and deuterium atoms. The study proposes a mechanism involving hydrated sulphuric acid aerosols to explain the observed water variations in Venus' atmosphere. These aerosols form above the clouds and rise to higher altitudes, releasing a higher fraction of deuterium-enriched aerosols. This process impacts the D/H ratio's evolution over time. The implications of these findings go beyond Venus, emphasizing the importance of altitude-dependent processes in understanding D and H reservoirs and predicting their evolution. By studying Venus' habitability and water history, scientists aim to gain insights into what makes a planet habitable and how to prevent Earth from facing a fate similar to its twin, Venus.