Enlarge / The spectral signature of phosphine superimposed on an image of Venus. (credit: ALMA (ESO/NAOJ/NRAO), Greaves et al. & JCMT )

Today, researchers are announcing they've observed a chemical in the atmosphere of Venus that has no right to be there. The chemical, phosphine (a phosphorus atom hooked up to three hydrogens), would be unstable in the conditions found in Venus' atmosphere, and there's no obvious way for the planet's chemistry to create much of it.

That's leading to a lot of speculation about the equally unlikely prospect of life somehow surviving in Venus' upper atmosphere. But a lot about this work requires outside input, which today's publication is likely to prompt. While there are definitely reasons to think phosphine is present on Venus, its detection required some pretty involved computer analysis. And there are definitely some creative chemists who are going to want to rethink the possible chemistry of our closest neighbor.

What is phosphine?

Phosphorus is one row below nitrogen on the periodic table. And, just as nitrogen can combine with three hydrogen atoms to form the familiar ammonia, phosphorus can bind with three hydrogens to form phosphine. Under Earth-like conditions, phosphine is a gas, but not a pleasant one: it's extremely toxic and has a tendency to spontaneously combust in the presence of oxygen. And that later feature is why we don't see much of it today; it's simply unstable in the presence of any oxygen.

Enlarge / A simulated view of Gale Crater Lake, measuring about 150km across, on Mars about 3 billion years ago. (credit: NASA/JPL-Caltech/ESA/DLR/FU Berlin/MSSS)

Mars clearly once had a lot of water—there are simply far too many features that clearly formed in a watery environment for that to be a matter of debate. What's less clear is how much of that water was liquid and for how long. While some features clearly indicate that liquid water was present for a long time , others likely formed under glacial ice .

It's not clear whether the differences are a matter of timing—a wet period followed by an icy one, for example—or due to regional differences in Mars' climate. It's difficult to tell in part because we can't get climate models of Mars to produce a climate that's wet enough for long enough to form a lot of watery features.

To try to put some constraints on what the ancient Martian climate might have looked like, a team of planetary scientists decided to take a careful look at some of the once-watery features identified on the surface of the red planet. Timothy Goudge, Caleb Fassett, and Gaia Stucky de Quay (yes, that's a planetary scientist named Gaia) identified a series of lakes, and used the features of the lakes to put some constraints on the precipitation that fed them.