Free Astronomy Magazine July-August 2021

JULY-AUGUST 2021 A size comparison of Earth (image taken by the Apollo 17 crew) and Venus, showing their similar size, but very different surfaces. [NASA] Past or current habitability − With a mean surface temperature of 464 °C (867 °F) and only the scant presence of water vapor detected in the at- mosphere, it is very difficult to con- ceive of extant life of any form on the Venusian surface. As space en- thusiasts of all kinds were made well aware of during the presenta- tion of possible phosphine detec- tion during October 2020, the situ- ation changes dramatically with al- titude (for more information, see the November-December 2020 is- sue). At 50 km (30 miles) above the surface, conditions could be consid- ered reasonable (albeit highly acidic), even if only for what we would consider extremophiles on Earth. While the many re-analyses of the original phosphine detection seem to discredit the results of the original study, the first announce- ment clearly motivated people to think about how life might be thriv- ing on a planet that most thought far too extreme to even support long-term robotics missions. Just as Mars has been revealed to have been water-rich in its past, so too have researchers hypothesized on the conditions of an ancient Venus. Computational modeling performed at NASA’s Goddard Insti- tute for Space Studies in 2016 hint at the possibility that liquid water oceans once may have existed on Venus, but that these oceans may have also been a driver for the run- away greenhouse effect we see today. Over time and due to the in- creased amount of solar radiation incident on Venus due to its closer proximity to the Sun, the increasing water vapor in the atmosphere would have itself been broken down by UV radiation, leaving hy- drogen gas to escape into space and the reactive oxygen atoms and mol- ecules to slowly contribute to the production of carbon dioxide that now constitutes over 95% of the atmosphere. Studies of the atmos- A false-color image of part of Alpha Regio, the proposed landing site for the DA- VINCI+ descent stage, as originally taken by the Magellan orbiter. [NASA/JPL]