Panspermia: what is it, and to what extent has it been proven?

The panspermia hypothesis suggests that life on Earth could come from outer space.

Life is justified by itself, since the ultimate goal of every living being is survival, and therefore the propagation of its species in all the means that allow its development. To explain this "lust for life", interesting hypotheses are proposed, such as panspermia, which argues with reliable data that it is more than likely that we are not alone in the solar system.

When we look at the stars, we inevitably think of the infinity of the universe, since our solar system alone is 4.6 billion years old and has a diameter of 12 billion kilometers. These concepts are incomprehensible to the human mind, and therefore, it is easy to suspect that the idea of "life" as our mind conceives it does not serve to describe Biological entities external to the earth.

Dive with us on this astronautical journey into panspermia, or panspermia, or, in other words, the hypothesis that life exists in the universe transported by meteorites and other bodies..

What is panspermia?

As we have hinted in the previous lines, panspermia is defined as a hypothesis that proposes that life exists in the universe transported by meteorites and other bodies. hypothesis that proposes that life exists in all the universe and is in movement adhered on space dust, meteorites, asteroids, planetoids comets and also space structures of human use that transport microorganisms in an unintentional way.

Again, we emphasize that we are dealing with a hypothesis, that is, an assumption made on the basis of some bases that serves as a pillar to initiate an investigation or an argumentation. The information presented here should not be taken as a reality or an immovable dogma, but it is true that there is more and more reliable evidence to support the hypothesis presented here.

In addition, it should also be made clear that the concept of "extraterrestrial", which is grounded in the popular imagination, is out of place in the formulation of these ideas. At all times we speak of microorganisms or living beings analogous to them, not of foreign entities that are morphological aliens.not of morphologically complex foreign entities.

Having made these initial clarifications, let us look at the pros and cons of this exciting postulation.

Extremophiles and survival in space

An extremophile, as its name suggests, is an extremophile that is a microorganism that can live under extreme conditions. In general, these microscopic living beings inhabit those places where the presence of complex animals or plants is impossible, either because of temperatures, acidity, high amounts of radiation and many other deleterious parameters for "normal" entities. The question is obvious: can extremophiles live in space?

To answer this question, a research team exposed spores of the bacterial species Bacillus subtilis to space conditions by transporting them in FOTON satellites (capsules sent into space for research purposes). The spores were exposed to space in dry layers without any protective agent, in layers mixed with clay and red sandstone (among other compounds) or in "artificial meteorites"; that is, structures that combined the spores in and on rock formations that tried to mimic natural inorganic bodies in space.

After two weeks of exposure to space conditions, the survival of the bacteria was quantified according to the number of colony formers. The results will surprise you:

• Spores in dry layers without any protection were completely inactivated.
• The survival rate increased fivefold for spores mixed with clay and other compounds.
• Survival reached almost 100 % in spores that were enclosed in "artificial meteorites".

This only confirms an idea that has already been demonstrated in the terrestrial realm: ultraviolet radiation produced by sunlight is deleterious to living things on Earth when they leave the atmosphere. Even so, experiments like this one record that solid mineral materials are capable of acting as "shields" if they are in direct contact with the microorganisms carried on them..

The data presented here propose that rocky celestial bodies a few centimeters in diameter could protect certain forms of life from extreme insolation, although micrometer-sized objects may not provide the protection necessary for the preservation of life in space.

Lithopanspermia

Lithopanspermia is the most widespread and well-established form of possible panspermia.It is based on the transport of microorganisms by solid bodies such as meteorites. On the other hand, we have radiopanspermia, which justifies that microbes could be propagated through space thanks to the pressure of radiation from the stars. Undoubtedly, the main criticism of this last theory is that it largely ignores the lethal action of space radiation in the cosmos. How can bacteria survive without any protection from space conditions?

The example given in the previous section deals with part of the process of transporting microorganisms between planetary bodies, but the journey is just as important as the landing. Therefore, some of the hypotheses to be tested today are those based on the viability of microorganisms leaving the planet and entering a new one.

As far as ejection is concerned, the microorganisms should withstand extreme acceleration and shock forces, with the drastic increases in temperature must withstand extreme forces of acceleration and shock, with the drastic increases in temperature on the surface on which they travel on the surface on which they travel associated with these processes. These deleterious conditions have been simulated in laboratory environments using rifles and ultracentrifuges with success, although this does not necessarily fully confirm the viability of certain microorganisms after planetary ejection.

In addition to space transit, another particularly delicate moment is atmospheric entry. Fortunately, these conditions are experimentally simulatable, and research has already subjected microorganisms to entry into our planet via sounding rockets and orbital vehicles.

Again, spores of the Bacillus subtilis species were inoculated into granite rock bodies and subjected to atmospheric hypervelocity transit after being launched on a rocket. The results are again promising, because although the microorganisms located on the front face of the mineral body did not survive (this downward face was subjected to the most extreme temperatures, 145 degrees Celsius), those on the sides of the rock did.

So, as we have seen, from an experimental point of view, the presence of life in space mineral bodies seems plausible. Even if only barely, and under certain very specific conditions, it has been demonstrated that certain microorganisms survive during the various necessary stages of interplanetary travel..

An increasingly unsubstantiated criticism

The main detractors of the panspermia hypothesis argue that this hypothesis does not answer to the origin of life, but simply places it in another celestial body.t answer to the origin of life, but simply place it in another celestial body.. Yes, the first microorganisms could have arrived on earth inside meteorites and circulated in the universe, but where did these bacteria originally come from?

We must also bear in mind that this term was used in its most basic sense for the first time in the 5th century B.C., so that over the centuries, the detractors of this idea have argued that it is a process impossible to explain.

New scientific advances have been fighting this preconception for years, since, as we have seen, the survival of microorganisms in the planetary ejection, during the transit and after entering the atmosphere has already been demonstrated. However, a note is necessary: everything collected so far has been under experimental conditions with terrestrial microorganisms..

Summary

So, let's be clear: is panspermia possible? From a theoretical point of view, yes. Is panspermia probable? As we have seen in scientific tests, yes. Finally, is panspermia proven? We fear not yet.

As much as the experimental conditions have proven the feasibility of this hypothesis, the day has not yet come when panspermia will become a reality, the day has not yet come when a meteorite falling on Earth will bring us extraterrestrial life.. Until this happens, panspermia (especially lithopanspermia) will remain a hypothesis, which can only be elevated by irrefutable and indisputable proof. In the meantime, we humans will continue to raise our eyes to the stars and wonder if we are alone in the universe.

Bibliographical references:

• Ginsburg, I., Lingam, M., & Loeb, A. (2018). Galactic panspermia. The Astrophysical Journal Letters, 868(1), L12.
• Horneck, G., Rettberg, P., Reitz, G., Wehner, J., Eschweiler, U., Strauch, K., ... & Baumstark-Khan, C. (2001). Protection of bacterial spores in space, a contribution to the discussion on panspermia. Origins of Life and Evolution of the Biosphere, 31(6), 527-547.
• Napier, W. M. (2004). A mechanism for interstellar panspermia. Monthly Notices of the Royal Astronomical Society, 348(1), 46-51.
• Wickramasinghe, C. (2015). VIVA PANSPERMIA!. In VINDICATION OF COSMIC BIOLOGY: Tribute to Sir Fred Hoyle (1915-2001) (pp. 317-322).
• Bochkarev, N. G. (2017). Limits on panspermia. Astronomy Reports, 61(4), 307-309.