Sciency Words: The Unknown Absorber

Hello, friends!  Welcome back to Sciency Words, a special species here on Planet Pailly where we talk about those weird and wonderful words scientists like to use.  Today on Sciency Words, we’re talking about:

THE UNKNOWN ABSORBER

We’ve talked about this one before.  Several times now.  But given the recent news about Venus, I feel like this is a topic worth revisiting right now.

In 1974, NASA’s Mariner 10 spacecraft discovered that an unknown chemical in Venus’s atmosphere was absorbing copious amounts of ultraviolet light.  No one could figure out what this chemical could be.  And whenever science can’t figure something out, people’s imaginations tend to run wild.

What if this unknown ultraviolet absorber were a complicated chlorophyll-like molecule?  That would imply that some sort of organism, perhaps something like Earth’s cyanobacteria, was soaking up U.V. light and using it for some sort of alien version of photosynthesis!

Now you may be wondering how anything could live on a planet as absurdly hot as Venus.  Venus’s surface temperature is approximately 460°C (870°F).  But the unknown absorber wasn’t found on Venus’s surface; it was drifting around in the upper layers of Venus’s clouds, where the temperature is about 30°C (80°F)—almost Earth-like!  And as we learned in a previous Sciency Words post, microorganisms can (and do) use clouds as a habitat.

Don’t get too excited, though.  The unknown absorber was a mystery for a time, but in 2016 it was identified as a fairly simple sulfur compound.  At this point, there is no reason to think the formerly unknown absorber has anything to do with photosynthesis or any other biological process.  It’s just another weird chemical among the many, many weird chemicals found on Venus.

So when you hear about the discovery of phosphine in Venus’s atmosphere, and when you hear speculation about where that phosphine might be coming from, remember the story of the unknown absorber.