Sciency Words: Tholin

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Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us all expand our scientific vocabularies together. Today’s term is:


My travels through the Solar System have once again brought me to Titan, Saturn’s largest moon. My spacecraft has commenced landing procedures, and I am currently descending through a haze of aerosol particles called tholins.

The term tholin was coined in a 1979 paper co-authored by Carl Sagan. The word comes from two similar sounding Greek words, one meaning vault (as in the great vault of the heavens) and the other meaning mud. Apparently Sagan toyed with the idea of naming this stuff “star-tar.”

Back on Earth, tholins can be created in the lab. Just take some simple organic compounds like methane and ethane and zap them with UV light or an electric current. You’ll end up with this yucky, orange gunk all over the bottom of your test chamber.

Here on Titan, the same thing is happening due to photolysis. When chemicals like methane (CH4), ethane (C2H6), ammonia (NH3), and formaldehyde (CH2O) get irradiated by sunlight, they break apart and recombine as new, more complex structures.

Ag05 Tholins on Titan

Tholins fill the air as a dense, orange haze. They cover the ground below as orange sludge. They’re also starting to coat the viewport of my spaceship with an orangey film that, I suspect, will be a real pain to scrub off.

While tholins have been notoriously difficult to analyze in the lab, they seem to be a mishmash of organic molecules. It’s hard to say which organic molecules are present, but some of them appear to be extremely large, extremely complicated organic compounds.

It’s easy to imagine amino acids, peptide chains, or even some sort of proto-DNA emerging from tholins, provided the tholins are allowed to dissolve in some sort of aqueous solution (note to self: double check Titan’s liquid methane lakes for dissolved tholins).

I can’t say for certain if there’s life on Titan, but I have to admit with all these tholins lying around, conditions are ripe for some sort of biochemistry to get started.


What in the World(s) are Tholins? from the Planetary Society.

How Titan’s Haze Help Us Understand Life’s Origins from Astrobiology Magazine.

6 thoughts on “Sciency Words: Tholin

  1. Sounds like the orange crap I used to find all over the piping of my fuel cell back at my old job. I’d pump methane into the heated metal lines and this orange goo would begin forming over time. At least it dissolved nicely in acetone, which made cleanup a lot easier.

    Liked by 1 person

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