Very novice astronomer here. I keep seeing terms like "S-Complex" thrown around when talking about asteroids, but no matter how much Googling I do I can't figure out what that exactly means (every article just writes about it assuming the reader knows the definition).

Finally I looked up a free textbook and read the section on asteroids. In Composition and Classification it talks about there being three "types" of asteroids (another term I have seen thrown around): C-type, S-type, and M-type. (I've also seen them referred to as Type C, Type S, etc.)

So are the words "type" and "complex" just synonymous words to classify asteroids? If not, what does "_ -Complex" mean when talking about things like S-Complex asteroids?



1 Answer 1


Yes they are basically the same. The original asteroid taxonomies were defined from photometry (brightness) in a few filters such as the Eight Color Asteroid Survey of Tholen (1984). This resulted in asteroids with similar slopes being grouped together into the main complexes or classes. Once we got more detailed spectra of asteroids subtle differences between sub-members of e.g. the S-complex showed up and so the large complex was broken into more sub-classes such as Sc, Sq etc.


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