Last month’s news that phosphine (PH3), a toxic gas commonly produced by organic life forms, had unexpectedly been discovered in the middle layer of the atmosphere of Venus sent ripples through the scientific community—and made international news. To put the discovery into proper perspective, we turned to Susanna Widicus Weaver, the Vozza Professor of Chemistry who also has an appointment in the Department of Astronomy. As she notes, there’s reason for excitement—and caution, as well.
Why does the discovery of phosphine in Venus’s atmosphere matter?
This group of researchers undertook this study to test a method of finding a “biomarker” for future studies of planets outside of our solar system. They never expected to find an actual signal. They were simply testing their methods. The Merriam-Webster Dictionary defines a biomarker as “Something (such as a chemical compound, isotope, or cellular component) that indicates or suggests the presence of a biological process indicative of life.” If this detection is later confirmed and the amount of PH3 that they calculate is truly as elevated as this study indicates, then life on Venus becomes one of a handful of likely explanations for that result. Other options include an as-of-yet undiscovered geological or atmospheric process that can result in large amounts of atmospheric PH3. But this molecule was specifically targeted because it is thought to be a great biomarker candidate. This means that life in Venus’ atmosphere is one plausible explanation for these results.
You’ve expressed some concerns about how media outlets are portraying this discovery. What caveats should we keep in mind?
The authors state this best in the first sentence of the last paragraph of the paper: “Even if confirmed, we emphasize that the detection of PH3 is not robust evidence for life, only for anomalous and unexplained chemistry." Unfortunately, this point seems to have been lost on the media.
Any scientific study relies on certain assumptions. Scientists base these assumptions on the best information available at the time. But with every assumption comes a caveat. If there is more than one assumption made, there is more than one possibility for factors that could change the interpretation of the results. That is the case with this study. The authors state many times that more lines need to be observed to confirm the detection. Beyond that, they also have interpreted the result in terms of what experts currently know about the chemistry of Venus. But no model is ever 100% complete.
Keeping these caveats in mind, this result is still very exciting. If the molecule is confirmed to be there through additional observations, and if its concentration is confirmed to be at the elevated levels inferred by this work, then this is a surprise. One possible explanation – and I stress here that this is only one possible explanation – is that there is phosphine-producing life in the atmosphere of Venus.
What is this discovery likely to mean for the future of our country’s space exploration efforts?
There is a telescope being built by NASA called the James Webb Space Telescope (JWST). One of its key scientific goals is to take spectra of the atmospheres of exoplanets (planets outside of our solar system) and search for biomarkers. This discovery makes the anticipation for and the potential science payoff of JWST incredibly exciting!
As a scientist and professor of chemistry, what excites you most about a discovery like this?
Instead of using chemistry to probe the physics of the universe, I focus on studying how physics influences the chemistry of the universe. New discoveries of unexplained chemistry in space are exciting science puzzles waiting to be solved. Phosphorous chemistry in general is very poorly understood in the interstellar medium. It’s fascinating to me to see this puzzle also appear in a planetary atmosphere. There is so much cool chemistry out there in the universe that we don’t yet understand! This is what motivates my research and excites me about science.