In search of extraterrestrial life, scientists have long ‘followed the water,’ pointing their telescopes at Mars, once a wet world with a temperate climate. Recently, the icy moons Enceladus and Europa have also gained considerable interest owing to their subsurface oceans. Yet, a recent discovery has pointed to a new astrobiological frontier, a planet so inhospitable, few believed it could harbor life.

With a dense, acidic atmosphere made up mostly of carbon dioxide, the surface of Venus boasts crushing pressures of over ninety times that of the Earth at sea-level, and can reach stifling temperatures of over 400°C. Yet, only 50 kilometers above its surface lies a layer of clouds where the temperature and pressure drop significantly, reaching levels comparable to those on Earth. This atmospheric region could potentially support a habitable zone for biological life.

Using the James Clerk Maxwell Telescope in Hawaii, an international team of scientists were searching for signatures of molecules indicating life in this layer when they detected phosphine gas. The atmospheric conditions on Venus do not supply enough energy to produce phosphine spontaneously. On Earth, phosphine is found, but it is produced by a different source: anaerobic microbes. With non-biological sources such as volcanoes and lightning insufficient to explain the high density detected on Venus, living organisms have become a possible answer.

Scientists believe that Venus was once covered in water but suffered from a runaway greenhouse effect. As the planet dried up, microbes could have evolved protective outer layers to survive in the high-acid conditions, and could live airborne, riding the air currents. While this is an appealing hypothesis, the result is far from a definitive discovery of such extraterrestrial life. Even if life is not the source of Venus’s phosphine, however, the authors of the Nature Astronomy article have still discovered an unknown mechanism for phosphine production — a meaningful finding in its own right.

Professor Jane Greaves is an astronomer at Cardiff University, UK. This research was conducted in collaboration with 18 other researchers in the UK, USA, and Japan.

Managing correspondent: Melis Tekant

Original article: Phosphine gas in the cloud decks of Venus – Nature Astronomy

Media coverage: Is there life floating in the clouds of Venus? – BBC
Life on Venus?Astronomers See as Signal in its Clouds – The New York Times

Image credit: NASA