When we think of the universe, we imagine it as an inhospitable place, incapable of supporting life or minimally complex chemistry . Although it is true that the presence of life (neither present nor past) has been detected, we have detected a tremendous amount of biomolecules scattered throughout many corners of the universe . We have found these biomolecules in the atmospheres of the planets or moons of the Solar System, in the clouds of gas and dust that populate our galaxy and even in meteorites that have fallen to Earth from the confines of the Solar System.
Biomolecules are basically the set of molecules used by living beings to carry out their different functions . These can range from molecules as simple as the water we drink ( H 2 O ), the oxygen we inhale ( O 2 ), and the carbon dioxide we exhale ( CO 2 ) to the hundreds of different proteins that govern the internal mechanisms of our bodies. cells or the molecules that make up our DNA .
The most abundant molecule in any terrestrial living being is water , accounting for around 65% of the mass of a human being. This molecule is also very common in the universe. Only in our Solar System it has been detected in several bodies. We know that Mars has water ice in its polar caps and water in the form of mud under its surface, and water vapor has been detected being released into space by geysers at the south pole of the moon Enceladus, for example. All in all, we believe that there could be about 25 times more liquid water in the Solar System than on Earth . We don’t see it flowing across the surface of any planets or moons because most of it is under miles of ice.
Another place where a large number of organic molecules have been found is in the clouds of gas and dust that we can find scattered throughout galaxies like ours. These huge clouds, several light years in size, will form the seed from which a new star will be created in the future . Therefore, as a result of the material present in them (which consists of more than 90% hydrogen and helium, but contains hundreds of other different types of molecules) the planets, asteroids and comets that end up orbiting said star will also form.
Some 130 different organic molecules have been detected in this interstellar medium. Some of them, such as ammonia or formaldehyde , are believed to have been very important at the beginning of life on Earth. However, the most common type of organic molecule in these clouds are those known as polycyclic aromatic hydrocarbons (PAHs) . These molecules are relatively simple and consist of chains of carbon atoms arranged in different configurations. The largest of these molecules detected contained up to 13 carbon atoms. Although PAHs are not used by living beings directly, many molecules can be created from them that are very useful for life. Chlorophyll and hemoglobin , which are vital in transforming sunlight into energy and transporting oxygen in the blood, respectively, contain derivatives of these molecules.
However, the truly complex compounds have not been detected in these clouds, but in comets such as the Murchison meteorite , which fell on Australia in 1969. We think this may be due to two factors. On the one hand, the most complex biomolecules may exist in the interstellar medium, but they are incredibly rare and are in the “deepest” parts, where they are protected from UV radiation, which would destroy them. On the other hand, a minimum surface may be necessary on which different simpler molecules can land and react . This surface could be found on comets or asteroids with the appropriate composition.
In this Murchison meteorite, which is a meteorite known as carbonaceous chondrites, a large number of organic compounds were detected: quite large lipid chains were detected that, submerged in water, can form rudimentary cell envelopes, the five nucleotides that form the DNA and RNA molecules of all living things here on Earth and up to 70 different amino acids . Amino acids are the building blocks of proteins and play important roles in many different biological processes. Of these 70 detected amino acids, only 6 are part of our biochemistry. In addition, these molecules had a similar proportion of both enantiomers (these molecules can present two similar but opposite configurations, one being the mirror image of the other), while biological processes usually favor the formation of one or the other enantiomer, but not of the other. both, so any contamination was ruled out .
All these molecules, which form spontaneously in interplanetary and interstellar space, were able to reach Earth during their formation on board meteorites . Furthermore, if they could form in such a hostile environment, in principle they could also form in our seas and on our rocks . In the same way, we expect that these compounds are relatively common on other planets, in our solar system, but also in distant ones. Whether the leap from these compounds to something that can be considered alive is easy or difficult, the discoveries of recent decades will tell us. Hopefully it’s the first.
Referencias:
S. B. Charnley et al. 2002. Biomolecules in the Interstellar Medium and Comets. Advances in Space Research, 30 (6). DOI: 10.1016/S0273-1177(02)00499-4
