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One journalist defined Clara Sousa e Silva’s work as an “alien pum detector”; something very precise, as she says. The 33-year-old Portuguese astronomer says that for most of her adult life she was involved in searching for life markers on very, very distant planets. Many of them can contain oxygen, methane, carbon and other compounds essential for life and their derivatives. But all of these biomarkers are not unique to living things. The geochemistry of an inert planet can also generate them. From them it will never be possible to know if there is something alive in them or not.
This is where Sousa e Silva’s favorite compound comes into play: phosphine – with the official name phosphane – a gas that on Earth is produced by microbes associated with decomposition and death. “Someone compared the smell of this gas to that of the dirty diapers of a Satan baby,” he says in a virtual interview. Sousa e Silva belongs to Sara Seager’s team at the Massachusetts Institute of Technology (MIT), whose objective is to study all possible chemical compounds in the atmosphere of a planet that would indicate the presence of living beings. According to several previous studies of this group, if there is phosphine on a rocky planet with a moderate temperature, there is life.
In 2018, Jane Greaves, an astronomer at Cardiff University (UK), found traces of phosphine on Venus for the first time. She had been making observations for two years. But the results were inconclusive. Greaves contacted the MIT team, which had done various theoretical work on this gas as a biomarker, and together they prepared a new observation with a more powerful telescope, the ALMA in the Atacama desert. The results came in 2019 and were published today. “The phosphine signal was 15 times more powerful than the background noise,” recalls Sousa e Silva. The covid-19 pandemic has slowed down her investigation.
Question. In your study, how close are you to saying there is life on Venus?
Answer. Based on our knowledge of chemistry, physics, Venus, and spectroscopy, the most plausible explanation for the detection we have made is that there is phosphine. I’m also sure that the most plausible explanation for your presence, crazy as it may sound, is that there is life. But an extraordinary statement needs extraordinary evidence and we don’t have it yet. We don’t even deeply understand Venus. We need to look at more aspects of phosphine to confirm that it is this compound. This is our first problem. And then you will have to work hard until you confirm that your origin is life.
P. How should this discovery be interpreted?
R. Everyone must be skeptical; I am. We want the scientific community to analyze us and explain to us where we have failed, if we have. I have been studying phosphine for most of my adult life. After these years we find no other explanation for its presence in the observed quantities. We analyze all the possibilities without finding another explanation.
P. Why is there such a clear connection between this gas and life?
R. Phosphine is a horrible molecule that kills by interfering with oxygen metabolism. On Earth, the vast majority of phosphine is produced by anaerobic microbes. It is not toxic to them because they do not need oxygen to live. That seemed amazing to me, that there is all this life that has a horrible smell and that it could be a marker of life and planets where there is almost no oxygen. For most of Earth’s history there has been life without oxygen. So why rule out the possibility of life on planets without oxygen?
P. How do Earth and Venus compare?
R. The pressure and temperature in the atmosphere of Venus are very suitable for life. In addition, the atmosphere protects from solar radiation and lets through a little energy to be able to use it. On Earth there are much more hostile regions where there is life. But Venus is special and uninhabitable because it is extremely acidic. The acidity of Venus is much higher than that of the most acidic places on Earth. This means that if there is life in that environment, it must be based on a totally different biochemistry than what we know, a life that is not incompatible with sulfuric acid, for example. This is my hope for the “Venusians”.
P. Saturn and Jupiter contain phosphine and do not harbor life. Why Venus?
R. On these two planets, phosphine is produced in the heart of the planet, where there is enough heat and a lot of pressure to cause phosphorus to bind to hydrogen, two compounds with almost no compatibility under normal conditions. Then the phosphine rises and reaches the outer layers of the atmosphere, which is where we observe it. Until today, phosphine has only been found in gas giants and on Earth, and is associated with life. Now the question is whether on Venus it is due to an exotic geochemical phenomenon that we do not know or the presence of life.
P. How is it possible to confirm that there is phosphine on Venus?
R. My thesis was to characterize phosphine and I discovered that there are more than 16 billion states in which it can be observed. So far we have only been able to see one of them. To confirm this observation, we need to see more states. These observations were made in the microwave light spectrum. We do not know of any other molecule that emits at this wavelength and with that intensity. Phosphine is the most plausible explanation, but it needs to be confirmed. Now we intend to observe phosphine in the infrared spectrum. For that, we want to use IRTF on Mauna Kea and the SOFIA project, a Boeing plane that takes a telescope and reaches the upper layers of the atmosphere to make observations. Both projects were accepted, but so far we have not been able to carry them out due to the pandemic. The instrument to be used on Mauna Kea is from the University of Texas and someone from that institution needs to go to Hawaii to prepare the instruments and calibrate them, and at that time no one from Texas will go to Hawaii, quarantine, go up to the telescope and then pass another quarantine. We all have families and priorities and this is by no means the most urgent. The next possible date is January 2021.
P. If there is life on Venus, is it possible to capture and study it?
R. If there is phosphine, how do we show that it is due to the presence of life? This is much more difficult. So far we have managed to demonstrate everything that it is not: it is not due to lightning, it is not meteorites, it is not a photochemical process, it is not volcanism. But we must continue to exclude possibilities. Another of my intentions is to try to map how phosphine is distributed in the atmosphere of Venus. It changes during the day and night due to the solar cycle, which would be expected if the source is life forms. There are also seasonal cycles, which would also be compatible with the presence of life. Ultimately, until we go there to collect samples, we will have to remain skeptical. This would be a very expensive and distant mission, perhaps it will be done at some point.
P. Is it possible a robotic mission that can demonstrate that there is life without any doubt?
R. The only other phosphorous measurement on Venus was made by the Vega probe. It appeared more or less at the point where we now see phosphine. The probe detected phosphorous compounds, but did not have the technology to know exactly which one. But it is very controversial because many people think that this party came from the ship itself when it disintegrated. If we now try to send a mission that does not reach the surface, but to the clouds in its atmosphere, we would only need a spacecraft capable of withstanding acidity. It is not trivial, but it can be done. The ideal would be to do the analyzes in the place because if there is life on Venus, we shouldn’t bring it to Earth. They would be life forms that have adapted to living in a very hostile environment and are probably very toxic and dangerous for us.
P. What implications will this discovery have if confirmed?
R. If it’s life, it changes everything. It doesn’t just mean that we are not alone. It also means that if there is life on Earth and on Venus, life is much more common than we think. Perhaps the presence of life in the Universe is inevitable. This may mean that there are hundreds, thousands of different forms of biochemistry in the galaxy, including the solar systems closest to our own. It fills me with hope. If there is life on Venus, it will also exist in many other places.
