The search for extraterrestrial life is one of the main motivations behind our current efforts in space exploration and behind the development and advancement of the study and understanding of the universe. This life, if it exists, does not have to resemble current terrestrial life. However, by studying the chemical properties of life , the conditions that exist and have occurred on our planet and those that we can find in the thousands of worlds discovered orbiting around other stars, we can perhaps understand the different alternatives and direct our efforts where they can be most fruitful. In short, before detecting it, we must understand in broad strokes how life works at the most fundamental level, to know what exactly we should look for .
In recent weeks, several scientific advances have been published that bring us one step closer to detecting this alien life. Using photosensitive molecules (that is, they react to light), a team of scientists has reconstructed the conditions in which the first terrestrial organisms lived . With this effort they hope to learn to identify the signs left by the most primitive life , similar to that which existed on our planet before any organism learned to produce oxygen. This life lived in the oceans , in a world where oxygen was scarce in the atmosphere and where, as a consequence , there was no ozone layer (O 3 ) capable of protecting them from ultraviolet radiation from the Sun. These microorganisms developed rhodopsins , proteins capable of of transforming sunlight into energy , in a kind of primitive photosynthesis.
The energy present on the early Earth was probably scarce, as complex biomolecules did not exist in sufficient quantity to serve as food. These organisms therefore ended up turning to sunlight as a source of energy . We use a derivative of these rhodopsins in the rods of our eyes, the cells responsible for registering the intensity of the light we perceive. This team has analyzed rhodopsin sequences present in microorganisms from habitats around the world , to study how they have evolved over time. In this way they have been able to develop a kind of family tree of rhodopsins , reconstructing the molecules that must have existed more than 2.5 billion years ago .
Modern rhodopsins are capable of absorbing light of different wavelengths , from blue to orange light, thus showing pink, purple or reddish colors, as this is the light they reflect and do not absorb. However, primitive rhodopsins only seemed to absorb green and blue light . Since the primitive Earth in which these organisms inhabited lacked an ozone layer, it is believed that they lived several meters below the surface of the sea , in order to protect themselves from intense ultraviolet radiation.
By understanding the optical properties of these organisms, and the molecules they use in their metabolism, we can look for signs of their presence on distant exoplanets . Therefore understanding primitive life could give us clues about life in other corners of the galaxy.
On the other hand and simultaneously, a team from the University of Hawaii has developed a scientific instrument that could greatly facilitate the search for extraterrestrial life (even fossilized) on bodies in the solar system. The Compact Color Biofinder , as they have called the instrument, has been able to detect bioresidues (organic molecules, basically) in fish fossils over 34 million years old in the Green River rock formation , present in the states of Colorado, Wyoming and Utah, in the USA.
In the search for extraterrestrial life, the ideal is to find life that lasts today. However, finding fossilized organisms can also be a milestone and could allow us to study such organisms more intensively. This search is an important pillar of our special exploration efforts by space agencies such as NASA, ESA, Roscosmos or CNSA, as evidenced by the large number of instruments developed for this purpose .
Most biological materials leave behind molecular debris that can be detected by fluorescence . The researchers used a terrestrial fossil as an analog to what we might find on bodies like Mars or one of the moons of Jupiter or Saturn.
This instrument would make it possible to study large surfaces efficiently, in search of these biosignals. Although it cannot replace direct searches for biological samples, it can be an important support in these efforts, helping to define the areas where this direct search could be more fruitful.
Although we do not know how quickly biowaste is replaced by minerals in the mineralization process, especially in environments as different as those present in other bodies in the solar system, the results of the CCB show that on Earth they can last for millions of years. of years .
Its objective would therefore be to install one of these detectors on a Martian rover , so that it could take measurements from the ground. This could work even if the organisms present were microscopic, as long as they appear in sufficient numbers. This detection method also has the advantage of being non-invasive, as it does not require direct contact between the microorganism to be studied and the detector . Who knows, maybe we’ll see his instrument aboard a future mission to Mars.
Reference:
D. Cathryn et al, 2022, Earliest Photic Zone Niches Probed by Ancestral Microbial Rhodopsins, Molecular Biology and Evolution 39 (5) DOI: 10.1093/molbev/msac100
Anupam K. Misra et al, 2022, Biofinder detects biological remains in Green River fish fossils from Eocene epoch at video speed, Scientific Reports 12 (1) DOI: 10.1038/s41598-022-14410-8
