Life is justified by itself, since the ultimate goal of every living being is survival, and consequently, the propagation of its species in all the means that allow its development. To explain this “longing for life” hypotheses as interesting as panspermia are proposed, which argues with reliable data that it is more than likely that we are not alone in the solar system. Panspermia definition biology
When looking at the stars, it is inevitable for us to think about the infinity of the universe, since only our solar system dates from 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 conceived by our minds does not serve to describe biological entities external to the earth.
Dive with us on this astronautical journey into panspermia, or what is the same, the hypothesis that postulates that there is life 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 throughout the universe and is in motion attached to space dust, meteorites, asteroids, planetoid comets and also space structures for human use that they carry microorganisms unintentionally.
Again, we emphasize that we are faced with a hypothesis, that is, an assumption made from a few bases that serves as a pillar to initiate an investigation or an argument. Much less the information presented here should be taken as an unchanging reality or dogma, but it is true that there is more and more reliable evidence that supports the hypothesis that we present here. Panspermia definition biology
Furthermore, it must also be made clear that the concept grounded in the popular imaginary of “extraterrestrial” is out of place in the formulation of these ideas. At all times we speak of microorganisms or living beings analogous to them , not morphologically complex foreign entities.
Once these initial clarifications are made, let’s look at the pros and cons of this exciting application.
Extremophiles and survival in space
An Extremophile, as its name suggests, is a microorganism that can live in extreme conditions . In general, these microscopic living beings inhabit those places where the presence of complex animals or plants is impossible, either due to temperatures, acidity, high amounts of radiation and many other parameters that are harmful to “normal” entities. The question is obvious: can Extremophiles live in space?
To answer this question, a research team exposed the spores of the bacterial species Bacillus subtilis to space conditions, by transporting them on 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 spores in and on rock formations that tried to mimic natural inorganic bodies in space. Panspermia definition biology
After two weeks of exposure to spatial conditions, the survival of the bacteria was quantified according to the number of colony formers. The results will surprise you:
- The dry layered spores without any protection were completely inactivated.
- The survival rate quintupled in spores mixed with clay and other compounds.
- Survival reached almost 100% in spores that were encased in “artificial meteorites.”
This only confirms an idea that has already been demonstrated in the terrestrial sphere: the ultraviolet radiation produced by sunlight is deleterious for living beings that inhabit the earth when they leave the atmosphere. Even so, experiments like this record that solid mineral materials are capable of acting as “shields” if they are in direct contact with the microorganisms carried in them .
The data presented here propose that rocky celestial bodies with a diameter of a few centimeters could protect certain forms of life against extreme insolation, although micrometric-sized objects could not provide the necessary protection for the preservation of life in space.
Lithopanspermia is the most widespread and well-established form of possible panspermia , and is based on the transport of microorganisms through solid bodies such as meteorites. On the other hand we have radiopanspermia, which justifies that microbes could be spread through space thanks to the pressure of radiation from stars. Without any doubt, the main criticism of this last theory is that it largely obviates the lethal action of space radiation in the cosmos. How is a bacterium going to survive without any protection from space conditions? Panspermia definition biology
The example that we have provided here in the previous section responds to a part of the transport process of microorganisms between planetary bodies, but the journey is just as important as the landing. Therefore, some of the hypotheses that must be tested the most today are those based on the viability of microorganisms when 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 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 have to fully confirm the viability of certain microorganisms after planetary ejection.
In addition to space transit, another particularly delicate moment is the atmospheric entry. Fortunately, these conditions are experimentally simulable, and research has already subjected microorganisms to entry into our planet using sounding rockets and orbital vehicles.
Again, the spores of the species Bacillus subtilis were inoculated into granite rocky bodies and subjected to the atmospheric hypervelocity transit after being launched in a rocket. The results are again promising, because despite the fact that the microorganisms located on the front face of the mineral body did not survive (this descending face was subjected to the most extreme temperatures, 145 degrees Celsius), those that were on the sides of the rock yes they did.
So, as we have seen, from an experimental point of view the presence of life in space mineral bodies seems plausible. Although it is with great difficulty and under certain very specific conditions, certain microorganisms have been shown to survive during the various necessary stages involved in interplanetary travel . Panspermia definition biology
An increasingly unfounded criticism
The main detractors of the hypothesis of panspermia argue that it does not respond to the origin of life, but simply places it in another celestial body . Yes, the first microorganisms could have reached the earth inside meteorites and were in circulation throughout 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 meaning for the first time in the 5th century BC. C., so that throughout the centuries, the detractors of this idea have been based on the fact that it is a process that is impossible to explain.
New scientific advances have been fighting this preconception for years, because as we have seen, the survival of microorganisms in planetary ejection, during transit and after entering the atmosphere has already been demonstrated. Of course, a note is necessary: everything collected so far has been under experimental conditions with terrestrial microorganisms .
So let’s be clear: is panspermia possible? From a theoretical point of view, yes. Is panspermia likely? As we have seen in scientific trials, too. Finally: is panspermia proven? We fear not yet.
As much as the experimental conditions have shown the viability of this hypothesis, the day has not yet come when a meteorite fallen on Earth gives us extraterrestrial life . Until this happens, panspermia (especially lithopanspermia) will remain hypothetical, which can only be raised by an irrefutable and indisputable test. Meanwhile, human beings will continue to look up at the stars and wonder if we are alone in the universe.