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Skywatching

Cosmic dust in your eyes

Dust might not sound like a very exciting subject compared with, say, black holes, but actually it is.

Not only is it the raw material for making new planets, asteroids and other bodies, it also provides an environment for all sorts of other important and fascinating things to happen.

Most of us have suffered from sunburn. This happens because overexposure to solar ultraviolet rays results in damage to the complex organic molecules making up our skin. Moreover this is after our atmosphere has filtered out most of this dangerous radiation.

However, over the last few decades, we have found space to be loaded with fairly complex organic molecules.

How can this happen?

In addition to being very cold and a near vacuum, space is flooded with ultraviolet light. The answer is surprising, dust.

In most places, space is fairly clear, making it possible for our telescopes to reach far out into space, and back in time to almost the beginning of the universe.

However, in some directions we see great dust clouds, thick enough to block the light of the stars lying behind.

Tis summer, if you are somewhere with a dark, clear sky, look into the southern sky. You will see the Milky Way apparently splitting into two streams. Of course, there is really only one stream, but there is a thick belt of dust down the middle that blocks out the stars.

Inside these dust clouds, the ultraviolet is blocked, and it is very dark and cold. Thanks to previous generations of stars, the clouds are loaded with all the elements produced as waste products by those stars.

This makes the clouds excellent places for chemistry to happen. At such low temperatures, chemicals react very slowly, but there is lots of time — billions of years. The result is an incredible witch’s brew of organic chemicals.

Ultraviolet light penetrating the outer part of a cloud can break a molecule into fragments. When this happens in the Earth’s warm, dense atmosphere, those fragments won't last long.

Inside those dark, cold clouds things move slowly and the chance of colliding with something is low. So the fragments can slowly diffuse more deeply into the cloud.

If by some small chance, two fragments do run into one another, they will almost certainly bounce apart again, like billiard balls.

In this scenario, with collisions infrequent and unlikely to result in larger molecules, reaction rates would be very low. This is where the dust comes in.

It provides somewhere for chemical reactions to take place. The rough surfaces of the dust grains provide lots of opportunities for the molecule fragments to bounce around until they come to rest on the surface.

There they sit while more molecular fragments slowly accumulate. Chemical reactions take place and the grain becomes coated with complex, organic molecules.

Then, when a cloud becomes unstable, collapsing under its own gravity and forming a new planetary system, those planets receive a ration of the organic molecules that can, under the right conditions, form the basis of life.

This is why there are more optical and radio telescope hours dedicated to studying dust than are spent looking at or for black holes.

We look for the radio and infra-red signatures of the organic molecules in the clouds, and try to deduce the reactions slowly taking place, and we look at these dust clouds as they form protoplanetary discs, the beginnings of new planetary systems.

The current situation is that we are finding many times more molecular signatures in those clouds than we have managed to identify. Whatever recipe for life we consider, the ingredients are probably there, providing the conditions on the new planet are suitable.

We know it happened at least once.

  • Mars lies low and inconspicuous in the west, sinking slowly into the twilight as it moves toward the other side of the sun.
  • Jupiter, shining like a searchlight, rises around 1 a.m.
  • Saturn rises at 3 a.m.
  • The moon will be new on the 4th.

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About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]



The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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