Venus has dark streaks in its clouds and nobody knows what they are
Something small caught my eye today and I have been thinking about it since.
In normal light, Venus just looks like a bright plain ball. Photograph it in ultraviolet, though, and you see dark streaks moving across the tops of the clouds. People have been looking at those streaks for over a hundred years and still cannot say what makes them. Astronomers just call it the "UV absorber".
There is a new paper in the journal Astrobiology from Jan Spacek and an international team, and it takes a different approach. Instead of guessing which chemical it is, they asked a simpler question. If you scooped up the liquid inside those sulfuric acid cloud droplets, how dark would it have to be to explain what we see from here?
They ran a radiative transfer model and got a number. The liquid would need to soak up ultraviolet and blue light very strongly, with an absorption coefficient of roughly 1,278 per centimetre at 375 nanometres. That is a lot of darkness for something that looks pale yellow from outside.
Then they checked what could actually hit that number. Certain organic molecules could do it at a few to a few tens of grams per litre. A lot of the inorganic candidates people have suggested would need to be far more concentrated than seems likely.
The authors are careful about what this means. They are not claiming they found life, and they are not naming the absorber. What they have done is set a bar. If you want to propose a candidate now, you have to show it can be that dark at a sensible concentration.
I like this kind of result. It does not solve the mystery, but it does narrow down what the answer is allowed to be.
Source: https://www.sciencedaily.com/releases/2026/09/260912220022.htm