Ken Tapping, January 25, 2006

In fairytales, a pinch of stardust is what makes special things possible. This is actually not far from reality; it is used to make planets, stars, and even us. It is really interesting stuff, and we wanted to get hold of some. Last weekend that wish came true when a spacecraft returned to Earth with a small sample.

When our universe began about 13 billion years ago, it consisted mainly of hydrogen gas, with some helium and small traces of other elements, such as lithium. You cannot make planets or people from this mixture; most of the key ingredients are missing. However, parts of these clouds collapsed under their own gravity. The most compressed parts became hot enough for nuclear fusion to start, forming the first stars.

Stars use hydrogen as fuel. During their lives and final collapse or explosion, they produce all the other elements. When these early stars died, their material was released into space where it mixed with the hydrogen clouds. After a few generations of stars, the clouds became enriched with all the elements necessary to make planets and living creatures. Then things become even more interesting because the elements in the new cloud mixture started to react with one another, producing a rich brew of really interesting chemicals: such as water, ammonia, carbon monoxide, alcohol, methane, formaldehyde and so on. When we look at the radio signatures of the chemicals in these clouds, we see so many that most of the chemicals have not been identified yet. If we put a mixture of the most common primordial chemicals in a bottle and pass electrical sparks through it, we end up with aminoacids – the building blocks of proteins – the key ingredients for life as we know it.

To learn more about the processes that produced our world and the life on it requires us to know more about the original ingredients. We needed some stardust. That would not be easy. The material making up our Earth has been processed and changed. Using that to deduce what we started with would be like trying to visualise a rice plant by looking at a bowl of rice pudding! Space near the Earth is no good either. The material there comes from the Sun, blowing in the solar wind. To get the original ingredients we would have to visit the extreme outer reaches of the Solar System. Getting there is rather difficult. Luckily on occasion, visitors from those cold, distant regions come to visit us.

Comets are lumps of primordial material that have been deflected from the cold, dark outer Solar System so they come closer to the Sun, where we live. The solar heat evaporates the comet material forming beautiful tails. By flying a spacecraft through this cloud of evaporating material, we can collect a small pinch of stardust. That has been done, and a few days ago the spacecraft dropped off a capsule of this precious material. It landed safely on Earth and over the next few months we will start learning some really interesting things.

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Ken Tapping is an astronomer at the National Research Council Herzberg Institute of Astrophysics (NRC-HIA), and is based at the Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9 Tel (250) 493-2277, Fax (250) 493-7767,
E-mail: ken.tapping@nrc-cnrc.gc.ca