The Astronomer’s Periodic Table

I discovered this a little while ago and have been meaning to post about it for a while. Another reason why us astrochemists are a bit atypical by the standards of virtually all other chemists…

The astronomer’s periodic table. Effectively, this is what people like me have to work with. How abundant any one element is is shown by the size of its white square. All other elements combined would probably fit inside a single pixel in this image — possibly with room to spare.

Pretty amazing, huh? Several of those wonderful elements which are essential components of us living creatures (like phosphorus, calcium and sodium) are really quite rare on the grand scale of things. So rare, in fact, that it takes a huge ball of iron and silicates (like Earth) to gravitationally scoop up enough of them for us to exist at all.

This is also why we don’t do any astrochemical searches for funkier chemicals in interstellar space. Things like phosphines, boranes and uranium oxides probably all exist in the interstellar medium. There’s no good reason why they shouldn’t. The thing is, there would be so little of them out there that we could never ever detect them!

So instead, we limit ourselves to elements we actually have a chance of finding. Incidentally, looking at that image, you can also see pretty easily why the most common molecules in the Universe are H2, CO and H2O!

Image half-inched from the McCall Research Group website.

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
This entry was posted in Imported from Livejournal and tagged . Bookmark the permalink.

8 Responses to The Astronomer’s Periodic Table

  1. Clouthier. The grad student who actually found the spectrum hidden in some old HCP data was Fumie Sunahori, who is an incredibly fun and awesome person. Perhaps someday you’ll meet her :)
    I have to admit I’m much more interested in astrochem since I started reading your blog. :)

  2. helen99 says:

    I’m happily surprised that Oxygen and water are so common.

  3. invaderxan says:

    You know, the chemist half of me still twitches whenever I say that. :P

  4. invaderxan says:

    Hmmm… Yes, perhaps that was worded badly. I probably should have said that several elements are rare.
    It does certainly help astrobiologists though. For instance, while biochemistries with other elements and solvents are possible, the abundance of those gives a set of constraints. So it’s possible to say, for example, that boron is unlikely to be a significant factor in an alien biochemistry. :)
    It’s also notable that hemoglobin and chlorophyll feature porphyrin rings containing Fe and Mg, respectively.

  5. pax_athena says:

    And don’t forget to mention that any element that is not hydrogen or helium is a metal ;)

  6. 6_bleen_7 says:

    The most common elements in biological macromolecules—C, H, O, N, P and S—all appear on the diagram, with the exception of P. Hence, if you look at what is unique to life, we’re not all that unusual.
    However, the “ionic” constituents of life—Na, K, Cl, Fe, etc., don’t appear, except for Fe and Mg, so we can at least claim that distinction.

  7. invaderxan says:

    Right — Is he Halfen, Clouthier or Ziurys? :D
    And yeah, there’s certainly phosphorus out there. Lots of it, too. It’s created by the oxygen burning process in massive stars, as well as (I think) the s-process in AGB stars. It’s just that by contrast to everything else, there’s hardly any. On that picture above, sulfur is the least abundant element, and there are two orders of magnitude more sulfur out there than phosphorus!
    Thing is though, the star IRC+10216 is an old AGB star, so it’s had a chance to accumulate lots of heavier elements — and they’re all still conveniently concentrated around it. Plus, it’s really nearby (the closest AGB star to Earth, I think?). It’s a particularly well studied star for just that reason!
    …*ahem*
    Sorry. I think I geeked out a bit back there. ;)

  8. There has to be a trace of phosphorus in space…my quantum prof found CCP there :)

Comments are closed.