Meteor Chemistry

Have you ever noticed that not all meteors you see falling are the same colour? Growing up in the dark countryside away from city lights, I saw them sometimes, and their colour occasionally seemed to be an unusual and striking shade. Other times entire meteor showers tend to be a certain colour (the Quadrantids, for instance, tend to be blue). The reason for this is all down to what chemical elements are found in the meteors.

I stumbled across this image from AccuWeather.com somewhere on the internet and thought it seemed pretty cool. It’s a handy little chart for determining what’s in a meteor based on its colour.

The purple ones are pretty rare.

These look accurate to me. Incidentally, a flame test for Calcium shows a rich red colour, but in this case I’d assume that you don’t find Calcium without Magnesium, so you’d get purple. As for the oxygen/nitrogen meteors, I’d guess the colour is due to chemical compounds in the meteor breaking down. Atomic oxygen emits red light when it’s excited. Which is actually why aurorae are red after heavy solar storms, when charged particles from the sun are energetic enough to reach Earth’s inner atmosphere. There, they fragment oxygen atoms and make a red glow.

So now you can know a little bit more about what you’re seeing if ever you watch a meteor shower. Adds an extra dimension, I think…

I always love seeing a bright blue one. This one looks like it has a tinge or purple too...

Image is “Fireball over Banff Rundle Mountain” © Brett Abernethy. His photos are spectacular and make me wish I had a better camera!

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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2 Responses to Meteor Chemistry

  1. ran190 says:

    Colors emitted by the substance when heated is not due to the breaking up of compounds but the from the substance’s electrons absorbing energy from the heat source. When the color actually appears from this , this is when the substance moves from a higher state of energy to a lower state of energy and this light that is actually called a photon. The energy emitted from the photon determines the color of the flame. This is from my chemistry class if you want to know more just look up the photons.

    • invaderxan says:

      I think perhaps your chemistry class hasn’t taught you everything quite yet. ;)

      You’re quite right that emission lines are due to electrons, but the thing is that electron energy levels are unbelievably sensitive. In the case of oxygen, the emitted photons from atoms, molecules, etc will be at different energies and therefore be at different colours.

      As an example, if you try to burn water, you won’t see red because the oxygen is present as H₂O. If you burn a regular flame in air, it will be burning O₂, but you won’t see red. The red colour is specifically from oxygen atoms, and you won’t ever see those unless a chemical compound is breaking down.

      Interestingly, when molecules break up, the remaining pieces tend to be full of energy, and they need to lose that energy somehow. For example, this reaction:

      Mg₂SiO₄ → Mg₂SiO₃ + O*

      Forsterite (Mg₂SiO₄) is one of the most common minerals in the universe, and a major component of everything from meteorites to planet Earth. This reaction needs about 110 kJ/mol to occur (which is pretty high). As a result, the oxygen atom which gets chopped off is written as O* to show that it’s in an excited state. That oxygen will then fall back into its ground state and emit a photon as it does:

      O* → O + hν

      And it’s that photon which you see emitting the red colour. (Or green colour, depending on how highly excited the atom is – the green colour of aurorae comes from oxygen atoms in the upper atmosphere).

      The full emission spectrum of oxygen looks like this:
      Auroral-emission
      But if there isn’t enough energy to get the atoms excited enough to show the green colour, red is all you get. Hence red coloured meteors.

      Thanks, kid. Say hi to your chemistry teacher from me. And ask them to tell you more about auroral emission. It’s pretty cool.

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