Humans on Mars

It would be wrong to send humans to Mars.

It might compromise forever the answer to the question of whether there is life on Mars.

We know that all Terran organisms carry their genetic information in RiboNucleic Acid(RNA), or its derivative DeoxyriboNucleic Acid(DNA). The plain 'acid' double helix is stabilised by a sequence of 'bases' in pairs that link the helices. The bases are denoted by their initial letters (A,G,C,T), and the genetic code is embedded in the order in which a given DNA strand carries them.

It has been shown in the laboratory that the code of this language, insofar as it describes protein synthesis, is arbitrary.

It follows that, since every known organism on Earth uses the same DNA language (or its RNA equivalent), every known organism on Earth shares the same ancestry. This applies even to organisms as different from us as Clostridium botulinum, which is poisoned by oxygen, and Desulfotomaculum auripigmentum, which uses arsenic as its metabolic oxidant.

Potential Damage

It also follows that if life arises separately from us on some other planet, whether in our Solar System or megaparsecs away, then even if it uses DNA or RNA as its genetic material, its genetic language is bound to be different from the one common to all Terran organisms.
So if a bacterium-like organism is found on Mars, and it shares our RNA language, we must conclude either that it is contamination like the starlings in North America, or that Fred Hoyle's wildly improbable hypothesis, Panspermia, is true.

Hoyle was brilliant, and had his own solution to the so-called Irreducible Complexity problem. Panspermia is the hypothesis that all life on Earth originated as 'seeds' in interplanetary space.

If all exploration of Mars is done with scrupulously sterilized robots, we might rule out the contamination alternative. But you cannot sterilize an 'astronaut'. All humans, probably all vertebrates, possess a population of beneficial bacteria necessary to their digestion and other health matters.

Protein Synthesis

An amino acid is a smallish molecule with an acidic end and a basic (base-ic) end. A protein is a long chain of amino acids, linked by the acid-to-base bond. Silk is a protein fibre, produced by silk moth larvae. It has been shown that the code for proteins is carried by sequences of 'codons' each codon consisting of three of the bases (or letters) given above. A codon is like a word in this language, and designates an amino-acid or a start or stop command. There are 64 codons, some of which are synonyms for the same amino acid. In actual protein synthesis, the cell carries out its assembly of a protein using special RNA molecules which link to the codon at one end, and acquire an amino acid with the other end. An experiment showed that the meaning of the words in a language could be changed. It was done by creating synthetic RNA molecules which specified different amino acids from the standard. Cells supplied with RNA from this non-Terran language manufactured different proteins!

Organic acids and bases

Carbon dioxide, dissolved in water, is a mild acid. It is called carbonic acid. Calcium hydroxide (lime, slaked lime) is a base. The two will combine to form calcium carbonate and water The most familiar acid in organic chemistry is probably acetic acid, the sour taste in vinegar. The usual structure of an organic acid contains a carboxyl group, which is a carbon atom linked to an oxygen atom and a hydroxyl group (OH). Each ribose-derived link in the helix has such a group, and can therefore link to a base.

DNA Bases

The helices are linked together by pairs of four organic chemicals called bases: adenine (A) and guanine (G) - purines,
and cytosine (C) and thymine (T) - pyrimidines.
Purines form hydrogen bonds to pyrimidines, with A bonding only to T, and C bonding only to G. These 'base pairs' serve to hold the DNA helices to each other.

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