A new study led by a research team from the UK and
German (with support from NASA) has shown that the existence of life may have
less to do with the quantity of water and more to with the presence of
atmospheric water molecules. As a result, we may have better luck finding life
on Jupiter’s turbulent cloud deck than Venus’.
The study that describes their findings, which was
recently published in Nature Astronomy under the title “Water activity inVenus’s uninhabitable clouds and other planetary atmospheres,” was led by Dr.
John E. Hallsworth of the School of Biological Sciences at Queen’s University
Belfast. He was joined by colleagues from multiple universities in the UK and
Germany, and the NASA Ames Research Center’s Space Science Division (SSD).
Venus has been the focal point of a lot of interest
lately, ever since the announcement that phosphine gas had been detected in the
planet’s dense atmosphere. These findings, according to a team of independent
researchers, were a possible sign that microbial life might exist in Venus’
sulfuric acid clouds (aka. a potential biosignature). However, according to
this latest study, Venus’ atmosphere doesn’t have enough water activity to
support this claim.
This conclusion is based on a new method devised by
Hallsworth and his colleagues to determine the level of water activity in a
planet’s atmospheres. They then applied this method on Venus’ atmosphere, where
temperatures range from 30 to 80 °C (86 to 176 °F) at altitudes of 50 km (30
mi) above the surface and water vapor accounts for about 0.002% of the
atmosphere by volume.
Ultimately, the researchers found that the water
activity in Venus’ atmosphere was over one hundred times beneath the lower
limit. When they applied this same method to Jupiter’s clouds, they found
something else entirely. Above the stratosphere-thermosphere boundary (320 km
above the troposhere) there is a “sweet spot” where temperatures are stable and
the clouds have a high enough concentration of water vapor.
In short, the clouds of Venus do not have what it
takes to support life, but Jupiter’s upper atmosphere does. This information is
highly significant at a time when NASA and other space agencies are proposing
various astrobiology missions for the near future. Before these missions can be
sent out to search for life, it’s imperative that we prioritize destinations
based on the likelihood of scientific returns.
As Dr. Hallsworth explained in a Queen’s University
Belfast news release:
“Our research shows that the sulphuric acid clouds in Venus have too little water for active life to exist based on what we know of life on Earth. We have also found that the conditions of water and temperature within Jupiter’s clouds could allow microbial-type life to subsist, assuming that other requirements such as nutrients are present.
“This is a timely finding given that NASA and the European Space Agency just announced three missions to Venus in the coming years. One of these will take measurements of Venus’s atmosphere that we will be able to compare with our finding.”
In addition, the results of this study present another
possibility for widening the search for habitable exoplanets. As it stands,
exoplanet characterization is focused on finding evidence of life on rocky
planets that have surface water. However, the detection of sufficient water
vapor in the atmosphere’s of gas giants – such as Exo-Jupiters and Exo-Neptunes
– could also point the way towards life beyond our Solar System.
“We have also performed calculations for Mars and Earth and show that these calculations can be done for planets outside our solar system,” added Dr. Hallsworth. “While our research doesn’t claim that alien (microbial-type) life does exist on other planets in our solar system, it shows that if the water activity and other conditions are right, then such life could exist in places where we haven’t previously been looking.”
Further Reading: Queens University Belfast, NatureAstronomy