Archive for February, 2013

Interstellar Ice

February 1, 2013

A couple of days ago I gave a talk at the Astrobiology Seminar about organic chemistry—IN SPAAAAACE. I chose the topic because I didn’t actually know anything about it to start out, so I learned a lot of cool stuff researching the talk. One of the things I learned is that ice (note that at ten degrees above absolute zero, “ice” can include things like frozen methane and ammonia as well as our old favorite water ice) is actually quite important to the formation of molecules in interstellar dust clouds.

Trifid Nebula

The Trifid Nebula, a hotbed (coldbed?) of interesting chemistry. From http://apod.nasa.gov/apod/ap130128.html.

Ice accumulates on tiny bits of rocky or sooty dust at the blazing rate of one molecule per day, and then acts as a surface on which chemical reactions can take place. Atoms and molecules just zipping around on their own tend to bounce off of each other, but on the surface of an icy grain they have time to get acquainted and engage in a little friendly covalent bonding. A surprising number of molecules can be built this way, including familiar ones like acetic acid, acetone, and ethanol.

Interstellar ice-grain chemistry could even be partly responsible for the “handedness” of chemistry on Earth, since circularly polarized starlight is one of the few known ways to create a bias toward left- or right-handed chemistry. What I didn’t know until researching this talk is that amino acids with a preference for left-handedness over right have actually been found in asteroids. The going theory is that a small initial bias toward left-handedness, perhaps created by interstellar polarized light, could have been amplified by as-yet-unknown chemistry inside the asteroid. Mystery!