Despite possible similarities in body chemistry, aliens may not look like us

The stuff of life

In a universe that must contain an enormous number of planets, with a good fraction of them “Earthlike", it is almost certain we are not alone.

That raises two interesting possibilities. Could it be that on any planet where some sort of processes can operate to produce life, and the ingredients are available, life is likely to appear? In that case, living things from different worlds could be bizarrely different, having evolved completely independently.

A second possibility is the seeds, or the basic stuff of life, are produced in space. When a new planet forms, it gets some of this stuff, and if possible, life develops and adapts to the environment in which it finds itself. This idea has come to be known as "Panspermia".

Decades of studying the composition and chemistry of the dark, cold dust and gas clouds between the stars suggest the Panspermia idea is more probable.

In galaxies like ours, the space between the stars, especially in the spiral arms, where we live, is filled with dark, cold, clouds of gas and dust. In many cases these clouds completely block the light from stars lying behind them.

Those clouds are the raw material for making new stars, planets and living things. In the youth of the universe, those clouds were mostly hydrogen and helium. But, as successive generations of stars were born and died, those clouds became enriched with the waste products from their energy production—the other elements. Although they are dark and cold, slowly, over billions of years, a lot goes on.

Radio telescopes make it possible to look inside those clouds to see what is going on, and also to detect results of a process of long, slow chemistry. So many signatures of organic (carbon-based) molecules have been detected that a large number have still to be identified. However, among those that have been identified are chemicals critical to the processes of life as we know it, including amino acids, the building blocks of proteins.

Proteins consist of careful arrangements of huge numbers of amino acids. Assuming those amino acids would happily come together to form proteins is rather like a pile of bricks moving together of their own accord to form a house. This rarely if ever happens, a fact for which the construction industry is grateful.

In Earthly life, the plan for assembling proteins from amino acids is encoded in our DNA. It has been proposed that this magical chemistry may have taken place in our primordial oceans, but as yet not exactly how.

Some new research suggests the production of really complex organic molecules works better in space. It is proposed that the cold, dark dust and gas clouds between the stars are a good place for complex molecules to very slowly come together, over millions of years.

The chemistry happens on the surface of minute dust grains. Carbon, molecules of carbon monoxide and ammonia, along with other things, get stuck to the grain and then react very slowly to form amino acids. Then, these can combine to form peptides, comprising anywhere between a few and hundreds of amino acids.

These have the property of promoting the chemical reactions that are important for life, including forming the membranes needed to enclose cells. Complex organic molecules, including amino acids, sugars and lipids (a family of organic compounds including fats and oils, also important for life) have been detected in meteorites.

That is not only evidence that complicated organic chemistry is going on, it shows how these chemicals might have got here.

Similarities in our body chemistries does not mean those aliens are going to look anything like us. The evolutionary path of life on Earth has been shaped by a series of processes and accidents that are probably unique in the universe.

The same will apply to the all those other worlds.


• Mars and Saturn lie low in the dawn glow.

• The Moon will be new on May 7.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.

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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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