A study that suggested that a chemical, which had been proposed to be a possible indicator of life, was found in Venus' atmosphere made headlines last year. Although life is impossible on the surface of the planet, it's possible that there may be milder conditions in its clouds. The possibility that the chemical was indicating the existence of life cannot be discounted immediately.Other researchers questioned the claims that the chemical was even present in the months that followed. Today, a paper has been released that suggests that Venus' cloud conditions are not compatible with life on Earth. Although temperatures are warmer in the clouds, there isn't enough water to sustain life. Most of the water in the clouds is made up of droplets of sulfuric acid.LimitsJohn Hallsworth, Queen's University Belfast, announced the results at a press conference. He said that the new research was inspired by the discovery of phosphine within Venus' atmosphere. His collaborators and he realized that the two areas of research could be combined to provide new ways to study the possibility of life on Venus. The other was a study on life in extreme conditions, partly driven by NASA's efforts to protect Mars from contamination.NASA also drove the second: probes were sent into the atmospheres on some planets to image them. Although these probes weren't designed to look for life, the data they collected provided measurements like temperature and pressure. This allowed us to set limits on the amount of water in the atmosphere and the shape it will take.People have discovered organisms that are able to maintain a metabolic rate within certain limits, such as temperature, acidity and water content. The temperature of the atmosphere changes with altitude. Therefore, it is important to limit altitudes that can be considered. These two factors are important because Venus is a very dry planet. Its clouds are not created by condensed water, but by sulfuric acid droplets, which would contain water.AdvertisementA salt-tolerant fungus holds the world record for living in dry conditions. It can perform a metabolism and undergo cell divides even when there is very little water. The water activity is a measurement that scientists use to quantify how much water is available. This is simply the amount of water available in a given environment, such as a humid atmosphere. It is equal to the relative humidity (the amount of water present versus what the temperature and pressure allow). It can also be measured using dissolved salts and ice formation.A microbe can survive down to pH -0.06, which is equivalent to having sulfuric acid make up a little over 10% of its solution. The rest of the solution is water.Rain is not always brought by all cloudsThis information is applied to Venus' conditions and the results are grim. The researchers calculated that Venus' relative humidity is below 0.4 percent, which is 100 times lower than what an organism can tolerate on Earth.The sulfuric acid is a problem if you believe that Venusian life could have developed methods to pull water from the dry atmosphere. Researchers calculate that droplets formed around sulfuric acids would contain so little water that their concentrations by weight would be at a maximum of 78 percent. With a little water, the droplets would be almost pure sulfuric acid.At this point, acidity of sulfuric acid is not as important as its ability to chemically destroy molecules and form new water molecules. This video shows how sugar converts to pure carbon after it is stripped of its water. The paper's authors list the following problems: "Sulfuric Acid dehydrates the cell systems, removes water biomacromolecules and reduces hydrophobic interactions. It also damages plasma-membrane integrity."The researchers have ruled out Venus and now they are focusing their attention on other parts of the Solar System. Based on data from probes that have scanned Mars' atmosphere, Mars' clouds are well below the temperature at which Earth's metabolism is shut down completely. Any water found on Mars is ice, which is then bombarded with enough ultraviolet radiation to sterilize. Also, Mars' clouds have been ruled out.AdvertisementWhat about Earth, Jupiter?The Earth's upper atmosphere may also be too dry for life. However, the troposphere can have a relative humidity anywhere between zero percent and 100 percent. However, most clouds in the troposphere will have water activity compatible with life. This is consistent with research that shows that many microbes may survive the journeys through the clouds they make.The most bizarre finding is from a look at Jupiter. It was visited by a probe dropped off during the Galileo mission. Although the probe fell through a dry area of Jupiter's atmosphere, we know that cloud bands can vary in composition and some are quite wet. Although ammonia can be a problem, it is usually found at higher altitudes than those that are compatible with life.Although there are many unknowns, it is likely that enough water will be available to sustain life at altitudes of -30 to 10 C.This is lifeResearchers note that the same approach could be used to study high-altitude life and provide details about the atmospheres on exoplanets. However, it won't give us any information about surface conditions (although some of these could be inferred using other data). Hallsworth stated that it excites him to be able pinpoint potential habitability using this data.Another thing to note is that this applies for life as it exists today: Water-based, with high use of hydrocarbons, and both hydrophilic & hydrophobic interactions. Different liquids would require different chemistries because they have different boiling and freezing temperatures. Although we don't have any evidence that life could exist within these liquids, it is still possible. Chris McKay, NASA's Ames Research Center, stated during the press conference that "part of me hopes, when we find life elsewhere, it will be really, really different."Nature Astronomy 2021. DOI: 10.1038/s41550021-01391-3 (About DoIs).
