What image comes to mind when you hear the words "molecular astrophysicist"? Most probably an old man working at NASA writing indecipherable equations on a board? And yet Dr.Clara Sousa-Silva is the complete opposite of those worn stereotypes, bright-eyed and keen to talk about her breakthrough research, which has now pointed to signs of life on Venus.
"I never tire of being a mother to phosphine," she jokes on the Zoom call, referring to her extensive research on the little molecule. Dr.Sousa-Silva is one of the few phosphine experts, having devoted much time and energy to finding and studying it. It is this chemical that she and her team detected in the upper atmosphere of Venus, pointing towards signs of biological life. She has experience working as a Research Scientist and 51 Pegasi b Fellow at MIT's Earth, Atmospheric and Planetary Sciences, at the Kavli Institute for Astrophysics and Space Research and is now working as a research fellow for the Harvard-Smithsonian Center for Astrophysics.
Last month, their research paper sent a buzz through the scientific community and the world as a whole, prompting renewed speculations on extraterrestrial life. Her effusive interest is only heightened when we ask about it. She pulls out a small molecular model of phosphine to illustrate her points.
"It's such a deceptively simple thing," she says. "But it takes tremendous energy put into a system to form it. Life, however, is willing to make that sacrifice."
Technically it is difficult to make phosphine, she explains. Even the component atoms - 3 hydrogen-bonded to one phosphorus – need certain conditions to come together.
"Phosphorous prefers oxygen. Hydrogen on the other hand doesn't really care for phosphorous. There's not a lot of free hydrogen, even in our own atmosphere but where it exists it prefers to go off with carbon, with water, with oxygen…"
Dr. Sousa-Silva reiterates that there is no (as of yet!) known mechanism that would produce the quantities of phosphine they have detected on Venus - other than biological pathways.
So why Venus and not Mars or Europa as is the usual suspect for hosting life in popular media? Dr. Sousa-Silva thinks it has to do with the hellish landscape of Venus that is so acidic that even our probes melted in the sulfuric acid atmosphere. "Even though the upper cloud decks are much more hospitable for life rather than say, Mars, which has such a thin atmosphere, people feel more comfortable thinking about the planet which won't melt your skin on contact," she laughs. She is confident that the planet will receive more attention from new generations of scientists than it did from hers.
Her enthusiasm for phosphine came at a heavy price though, and that was lack of interest even from others in her field. "Nobody was willing to listen," she recalls. "They were all convinced it was an unimportant and rather dangerous molecule." It was with the intervention of Professor Jane Greaves that her work began to truly take shape.
"Prof. Greaves was already investigating potential 'biomarkers' - signs of life – on other planets and encouraged her to pursue her research on the elusive phosphine.
"For example, chlorofluorocarbons are a good biomarker," Dr.Sousa-Silva says. "If they're in an atmosphere in large amounts they're being created by life and put there. So in my research, I have looked at dozens of exoplanets, in various ranges of habitability, looking for these biomarkers."
Earlier this year, there were news stories on unusual UV-absorbent patches in the atmosphere of Venus, which some speculated could be signs of photosynthesis. But Dr. Sousa-Silva is quick to point out that life there might differ from anything we imagine.
"Water may not be a limiting factor for Venusian life to survive," she says, referring to theories that Earth probes had contaminated the atmosphere with our own bacteria. "If there's life on Venus…small microorganisms, not like us - then it will be adapted to the unique conditions on Venus. Venus may have been habitable at one point but now our extremophiles would have a tough time in its highly acidic atmosphere, with such little water to go around."
Although it has been suggested to send working laboratories to Venus to sample the atmosphere in situ, Dr. Sousa-Silva has much humbler ideas about how to pursue this course of research.
"My team was split on this," she recalls. "One half wanted to build these…big flashy machines…and I didn't agree. I think we have so little fundamental data that even if we come across an inhabited planet, we won't even know how to look for life. I think we need more fundamental data. And the only way to get that is by funding and supporting PhD students and research scientists to focus on the remote analysis of data so we can understand what and how to look for life."
Without this base in research, it will be a waste of time and expense to send probes to distant planets and not know how to search for alien life, she says.
When it comes to working with students, her passion for encouraging science in the younger generation is visible. "I see a lot of fellow scientists who say: "Oh my research is too complex for students" and I say: No way."
Dr. Sousa-Silva, is the former Educational Co-ordinator for the Twinkle Space Mission where she founded EduTwinkle, the mission's educational program and started the ORBYTS program (Original Research By Young Twinkle Students), where high school students work along with scientists. She has even published papers with those students, remarking on their intelligence and curiosity and hopes she can do more to get more children into STEM careers and lay the groundwork for a better and more inclusive scientific community.
"After my PhD, I noticed the demographics narrowed the further up the ladder I looked," she says. "There was a serious lack of diversity. Even my professor, Jonathan Tennyson, who had equitable hiring practices struggled not to hire the same type of people over and over. It was because many people didn't have the right undergraduate backgrounds or the right high school subjects." Blaming "bad gatekeeping," of science, she hopes to see more young people involved in the scientific research of tomorrow.
So what are her future plans? Nothing that involves giving up on research into phosphine, evidently!
"We have identified around 16,367 possible biosignatures!" says Dr.Sousa-Silva. "So phosphine is one but that leaves 16,366 more. More research is needed but I'm convinced this is a very good biosignature…it has low false positives and is hard to confuse with non-biological processes. Oxygen and water can both be produced by a variety of abiotic mechanisms on a rocky planet…but, not phosphine, at least not as far as we know."
She is also quite happy with how the matter has been covered by the media.
"I didn't have enough faith in the press," she confesses. "Normally it's a lose-lose situation. If your research doesn't get picked up, nobody will hear about it, you won't get funding. And if it does, then the media oversells it. But I'm really happy with how this has been covered, there are no grand claims and the press has been really careful and sensitive."