Can there be life in space?

Earth, the third planet in the solar system. The blue planet, the only one that supports life organized in complex forms. At least, as far as we know today. What makes our planet so unique and suitable for the development of life forms?

The concept of habitable zone (also called the circumstellar habitable zone) was developed by astrobiologists in the second half of the last century to study how the mutual positions and properties of a planet and its star determine the probability of finding extraterrestrial life on other planets and systems.

Isaac Asimov

The subject of life in other places, together with the dream of one day inhabiting distant and uncontaminated worlds, has always fascinated entire generations. The idea of the habitable zone was first introduced to the general public in the 1960s, thanks to the famous and prolific science fiction writer Isaac Asimov and his series of books on the colonization of space.

More specifically, the term "habitable zone" refers to the region of space around a star within which planets with liquid water can be found. The role of water in the development of life on Earth has been crucial for the first biological processes and reactions that gave rise to the development of life, to the point that it is difficult to imagine strange worlds where life does not need this element. .

The importance of water for our planet and in space

The presence of water and the limits of the habitable zone depend on the physical characteristics of the star at the center of the planetary system, such as the energy it produces.. Consider our solar system as an example: the sun, an ordinary medium-sized star, radiates enormous amounts of energy. The Earth, about 150 million km from the sun (that is, 1 astronomical unit, or AU), receives this energy in just the right amount to provide a comfortable environment for the development of life.

The planets closest to the sun (Mercury and Venus) receive much more energy in the form of solar radiation and are therefore too hot and inhospitable for organisms in the terrestrial biosphere, which are highly dependent on the presence of water. By contrast, a planet like Mars is located too far from the sun to maintain its surface water in a liquid state.

Can there be life beyond in space?

It is necessary to consider that the development of life (or Earth-like life, since it is not possible to know with certainty the existence of different types of life in space that are not based on carbon*) depends on many other factors, in addition to the presence of water. First of all, the presence of an atmosphereThe atmosphere exerts enough pressure on the planetary surface, in space, to keep water in its most precious state, while allowing it to be (re)cycled through evaporation and precipitation.

The property of a planet to create an atmosphere that protects its surface and any biosphere from meteorite impacts, thermal excursions, and damaging radiation is largely tied to its mass. Low-mass planets do not generate, in some cases, a sufficient gravitational attraction to support the layers of an atmosphere, composed of light elements such as nitrogen, which easily escape the force of attraction exerted by the Earth. Exobiology and its relationship with extraterrestrial life It is a field of study that seeks to understand these relationships.

movement is also very important

In addition to the mass of the planet, the chemical composition of its atmosphere, and the amount of solar energy reaching it (or, in other words, its distance from the sun), the shape of its orbit plays an equally important role. The status of a "habitable planet" cannot be guaranteed if the orbit around the star is particularly eccentric, to the point of causing its regular departure from the habitable zone (for example, in the case where the planet reaches aphelion or perihelion, points respectively more distant and closer than the orbit of the sun).

The habitable zone of our solar system is between 0,5 and 3 AU wide. As illustrated in the figure: in the case of stars more massive and luminous than the sun, the habitable zone is located at a greater distance from the star itself because a greater amount of energy invests the planets (the exact amount scales with the square of distance). For smaller, fainter stars, such as dwarf stars, the habitable zone is closer to the star. Earth-like planets are of great interest in the search for life in space.

What would we be without the stars in space?

Stars also follow their own evolution, like planets and life on Earth, and go through phases of increasing luminosity, growth, or slow extinction, especially at the beginning and end of their existence. During these phases, the habitable zone changes accordingly. Our sun is currently in a stable evolutionary stage, approximately halfway through its life.

From the 1950s to the present, many planets located in the habitable zone of distant stars (exoplanets) have been identified and studied. These planets are generally larger and more massive than Earth, making them easier to detect with our astronomical instruments. With the development of more precise instruments and new search techniques, more and more Earth-sized planets have been discovered. Recent studies report that there may be more than 10 billion Earth-sized planets orbiting Sun-like stars. only in our galaxy.

desert planets in space

An interesting class of exoplanets are desert planets. These types of planets, where water is scarce, can be found in a larger circumstellar area than other planets for two reasons: 1) since they do not have ice and snow (white surfaces) in large quantities, they reflect less light and can maintain high temperatures even at greater distances from the sun; 2) thanks to the reduced evaporation of water and, therefore, to a lower greenhouse effect, it maintains temperatures suitable for life even at shorter distances than the typical Earth-Sun distance.

However, the concept of a habitable zone has been challenged, based on the hypothesis that liquid water could be present on other planets thanks to exothermic processes such as tidal heating or radioactive decay. Furthermore, water can be found in solution along with other elements, under different temperature and pressure conditions. This means that some worlds suitable for the development of life may exist outside the habitable zones, where we don't look for them.

The sun won't last forever

Stars are born, live, and die. The sun is no different, and when the sun dies, the Earth goes with it. But our planet will not go quietly into the night.

Rather, when the sun expands into space into a red giant during its death throes, it will vaporize the Earth.

Maybe it's not the story you were hoping for, but you don't need to start buying star-death insurance just yet. The timescale is long: 7 or 8 billion years from now, at least. Humans have existed for only about 40 thousandths of that amount of time; if the age of the Earth were compressed into a 24-hour day, humans would occupy only the last second, at most. If contemplating stellar lifetimes does nothing else, it should underscore the existential insignificance of our lives.

The brilliance that gives us life

So what happens when the sun rises? The answer has to do with how the sun shines. Stars begin life as large clumps of gas, mostly hydrogen, with a sprinkling of helium and other elements… Gas has mass, so if you put too much of it in one place, it collapses in on itself under its own weight.

This creates pressure inside the protostar, which heats the gas until it becomes so hot that electrons are stripped from the atoms and the gas becomes charged, or ionized (a state called plasma). The hydrogen atoms, each with a single proton, fuse with other hydrogen atoms to become helium, which has two protons and two neutrons. The fusion releases energy in the form of light and heat, which creates outward pressure and prevents the gas from collapsing further. A star is born (with apologies to Barbra Streisand).

Also read the article What would happen if the Sun went out?

What happens to Hydrogen?

There is enough hydrogen to sustain this process for billions of years. But eventually, almost all the hydrogen in the sun's core will have fused into helium. At that point, the sun will not be able to generate as much energy and will begin to collapse under its own weight. That weight cannot generate enough pressure to fuse the helium, as it did with hydrogen at the beginning of the star's life. But whatever hydrogen remains on the core's surface will fuse, generating a little extra power and allowing the sun to continue to shine.

However, that helium core will begin to collapse in on itself. When it does, it releases energy, though not through fusion. Instead, it simply heats up due to the increased pressure (compressing any gas increases its temperature). That energy release results in more light and heat, making the sun even brighter. On a darker note, though, the energy also causes the sun to swell into a red giant. Red giants are red because their surface temperature is lower than that of stars like the sun. Even so, they are much larger than their hotter counterparts.