The Voyager Golden Record: why is cytosine “S”?

/ nsaunders

Long time, no blogging. Breaking the silence with something a bit different than my usual content – a molecular biology question for you.

So a colleague posted this link to Yammer; a collection of images selected for the Voyager Golden Record. The record was designed as a “time capsule” illustrating aspects of life on Earth and was launched on the Voyager spacecraft in 1977.

image014

Chemical definitions

Three of the images are confusing me: chemical definitions (shown at right), DNA Structure and DNA Structure magnified, light hit.

You see why I’m confused, right? The symbol used for cytosine is “S”.

I’ve had two suggestions so far. First:

@neilfws I think to avoid confusion with ‘G’

Second – someone has suggested that they had already used “C” for carbon and wanted to avoid confusion.

Or – was “S” commonly used as the symbol for cytosine in 1977? I know it can mean “C or G”, but that does not make sense in this context. Or is it – surely not – an error?

My web searches on the topic are leading nowhere, so if you know the answer – let’s hear it!

8 thoughts on “The Voyager Golden Record: why is cytosine “S”?”

  1. I searched “s for cytosine” and on the 4th of 4th page got this weird result, which seems to have code corresponding from Reddit comments: http://coderedd.net/r/space/comments/wyyq1/the_images_of_voyager/

    it says:

    > ‘I had a book about the Voyager record as a kid (really interesting and I wish I knew where it ended up). From what the book said, the reason they chose S for cytosine rather than the universally accepted C was because the creators were worried that C might look too much like G on the recording. (edit: it was the remarkable [Murmurs from Earth](http://www.amazon.com/Murmurs-Earth-Voyager-Interstellar-Record/dp/0345283961))’

    I s’pose you could buy the book used for $40 or $65 and find out for sure.

    • An excerpt including Carl Sagan’s explanation was posted to a mailing list: http://groups.yahoo.com/group/SFGR/message/4183

      > We had to try to eliminate all possible sources of ambiguity, and it seemed ambiguous to use the same symbol for two different things: “cytosine” begins with a C, but we already had used a C to define carbon. I brought the problem up with Frank [Drake], and he shrugged and said, “Spell it with an S.” “Cytosine with an S?” I said dubiously. “The biochemists will have a fit.” “Do it anyway,” Frank said. “It’ll be a good object lesson in the special problems of communicating with extraterrestrials.” “Cytosine with an S?” [Stuart J.] Edelstein complained. I’m not sure our explanation convinced him.

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