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Curiosity for exobiology

2006/12/01 Rementeria Argote, Nagore - Elhuyar Zientziaren Komunikazioa Iturria: Elhuyar aldizkaria

Behind are the stories of the green little ones. The research of life outside the Earth, in a broad universe, is not science fiction, but encompasses different fields of science, and is called exobiology. They analyze how life arose on Earth to facilitate the search on other planets. The question behind all this is long ago: Is there life outside the Earth?
Curiosity for exobiology
01/12/2006 | Rementeria Argote, Nagore | Elhuyar Zientzia Komunikazioa

(Photo: ESA)
Exobiology is a science for some, for others it is a branch of biology. It is difficult to reach an agreement, but two data are enough to say what exobiology is: it combines many areas of knowledge and all work behind the answer to a question - is there life outside the Earth?-, in their respective areas.

The question is not the half-night cough of the goat. The answer, of course, does not know it, and is about to see if they will ever know it. But the effort is worth it, the search for the answer is so enriching.

To begin with, they will have to know where and what to look for exactly to find life. They investigate, among other things, how life on Earth arose. And there is a single model of life search outside the Earth: Terrestrial. Therefore, it is essential to know the conditions in which life arose on Earth (assuming it was so) to search for planets with similar conditions.

The truth is that it can be a very different kind of life in the broad universe. But the simplest thing is to find a life similar to what we know: based on carbon, in close relation to water, with some molecule of storage of information... In short, a system similar to that of the cell.

Since life on Earth is composed of carbon-based molecules, they believe that life outside of it will have the same base.
From file

At the limit of life

They seek the first living system, on the border between life and the inanimate. And the researchers adopt different paths to reach this border. From the biological point of view, for example, from the current living beings to time, one of the objectives is to analyze the evolution of the genes and know the genome of the first ones. From a chemical point of view they make the opposite way, that is, they leave the inanimate to reach the first living beings. Combining biology and chemistry, they study cellularity, looking for the first system that meets the definition of life.

One of the hypotheses is that this system was a single molecule, that is, before the cell there was a living system. To do this, this molecule had to meet two requirements: to store information (genetic code) and to be able to double. Currently this work is done by two types of molecules: DNA and enzymatic proteins. Some believe that before creating DNA, the RNA would perform both functions. This hypothesis is known as the world of RNA.

One of the proponents of the RNA world hypothesis is Sydney Altman, 1989 Nobel Prize. He discovered a strong argument in favor of the RNA world: A RNA catalyst (which has also found more). Therefore, the RNA, in addition to storing information, could be possible to perform enzymatic work and duplicate.

One of the exobiological debates is whether life arose on Earth or whether, on the contrary, it came from elsewhere, like a meteorite.
ANDÉN
One of the followers of Altman's ideas is researcher David Bartel, who assures that "we will never be able to prove that it was the world of the RNA because we cannot go back in time, but we can analyze the basic characteristics of the RNA and see if these characteristics coincide or not with the vision of the world of the RNA".

However, the main tendency is to think that the first living system was a cell. Some hypotheses consider it fundamental that the first living system is separated from the medium, separated by a membrane. The membrane is critical for any living system, since it controls the inputs and outputs of energy, so study the molecules that form it and its precursors.

So what to investigate

Other starting points for research. One of the characteristics of life is that some molecules, such as amino acids, are a certain isomer (although in nature both isomers are in the same amount), so some research is directed to the difference between isomers. The proportion of isotopes is also special in living beings, so others also act behind these isotopes.

Life appeared shortly after having the right conditions to create life on Earth, then living beings were greatly diversified. And evolution continues.
NASA-ARC

Another fundamental issue is when and how life arose. As Altman said, we cannot go back in time, but astronomers and geologists try to approach this time with the traces they have today. They study the genesis of the Earth and the whole solar system, as well as when and under what conditions life was born. In this way, we could search for other planets that meet these conditions.

It is true that the Earth also lives in very harsh conditions: extremophiles are an example of this: bacteria that eat iron, that live in very acidic means like Tinton River or salts... However, experts do not believe that life arose spontaneously in an environment like this, but it arose in mild conditions and some living beings evolved to adapt to harsher conditions.

However, in exobiology, extremophiles are also investigated, but not because they give the key to the origin of life, but because they can give some clue about where to find life outside the Earth.

In the geisers of Yellowston (USA) there are extreme conditions, but there are living beings.
(Photo: ANDÉN)
What is clear is that to create life you need a suitable environment. Analyzing microfossils, it is estimated that life on Earth occurred about four billion years ago (the oldest fossils are three thousand five hundred million years ago). Apparently, up to four thousand five hundred million years ago, the Earth was filled with meteorites, so it was not a suitable place to create life or to survive. Then came a quieter era, with ideal conditions for life, and soon emerged the first living systems.

Hypothesis hypothesis hypothesis hypothesis hypothesis hypothesis hypothesis hypothesis

However, there are those who think that life did not arise on Earth, but came from another place (brought by a meteorite). It is a hypothesis called exogenia -- better known as panspermia, but more limited than this --. Life appeared somewhere in the universe, then came to Earth, and as here had the right conditions, it multiplied and evolved.

Simulating the possible spatial conditions, through different experiments, they have discovered that some basic molecules for life can be generated spontaneously. The most classic experiment on the genesis of life is that of Miller (1953), who caused electric shocks to a mixture of methane, ammonia, water vapor and hydrogen, resulting in several amino acids (some of the basic molecules of life). Along this path, other experiments have been carried out to obtain complex organic molecules from common compounds in space or other planets, such as ultraviolet radiation, which is very abundant in space.

They still hope to find traces of life on Mars, current or ancient.
NASA-JPC

Another argument used by supporters of the exogenous hypothesis is the meteorite ALH84001. It was discovered in Antarctica in 1984 and, according to some NASA exobiologists, the nodules contained in the meteorite are very similar to those produced by bacteria. Therefore, it is possible that these structures have been created by some living being, but for the moment they do not know.

The meteorite is about four thousand five hundred years old and comes from Mars. In fact, within the exogenous hypothesis, there are those who think that life arose on Mars. The Marcians, more suitable than the conditions of the Earth, were created at that time. And they say that life was born on Mars and then came to Earth. That is why efforts have been made to find life tracks on Mars and will continue to be made.

In addition to Mars, life could be present on other planets and satellites (or could be, time and time should also be taken into account and in exobiology). Next to Mars, the podium is composed of two satellites: Europa de Jupiter and Titanes de Saturn. That in our solar system, but in general we look at distant planets. In the last decade, countless exoplanets have been found, so they believe that our solar system is quite normal in the universe and that there can be many more planets like Earth.

On that path, they investigate the habitability of the planets: if a planet meets or has never fulfilled the conditions to develop its life. It must be taken into account that when investigating the distant planets, they have a great technological limitation. And, therefore, they determine the size of a planet, the atmosphere, the distance to the Sun, etc., to which it must be adjusted to be able to find life in the best conditions. Thus, there are about 50 planets that can have life and from time to time are news of this type.

Meteorite found in Antarctica (left) with remains of some alleged living being (right seen under a microscope).
(Photo: NASA-JPC)

Game of odds

But as technology advances, the number of planets that can have life changes. The probability that in the Universe there are other lives other than that of the Earth is measured mathematically, but logically it is necessary to use the data provided by technology to use mathematical tools. And they still do not know that probability. For example, the result of the Drake equation cannot be determined.

Astrophysicist Frank Drake proposed an equation to calculate the number of possible technological civilizations in the universe. This amount depends on seven factors: The number of stars created annually in the Milky Way, the percentage of stars that surround the planets, the proper orbit to the life of a few of those planets, including the number of times that life has occurred, the number of times that intelligent life has developed in which life has occurred, and how many of them have developed technology (and the desire to communicate). In addition to these six, there is a correcting factor that takes into account time: the duration of this intelligent and technological civilization.

In the central image is our solar system, and in both we see how the distance between a planet and the star -- depending on the size of the star -- changes to make the planet habitable.
ESA ESA

As seen, all these factors vary with discoveries. And this equation has no result. Yes, it seems that astronomical factors give a much more optimistic image than that provided by biology, so biology is the biggest limitation to developing an intelligent life.

However, despite the existing uncertainties, there is a large project underway for a long time in the search for technological civilizations: SETI. As its director Jill Tarter said at the 2006 General Assembly of Astronomers: "Although there are many civilizations, it is not surprising that no one has yet been detected." In fact, they explore the sky in search of radiofrequencies, directed at each moment to a specific point, and in each of these points they work with nine dimensions: the three corresponding to space, time, frequency, sensitivity...

Jill Tarter is director of SETI. It was based on this woman to shape the protagonist of the novel Carl Sagan Contact.
SETI Institute
It will not be easy to get right full. According to Fermi's paradox, as on Earth there is life, in any other corner of the universe life will be a normal event and an intelligent life. And if intelligent life is normal, then your footprints should be visible. That is why SETI expects these tracks to appear.

However, more than one will wonder why they have not contacted if there is intelligent life. Experts approach the question with good humor and more than one has responded in jokes, such as Stephen Hawking: "Seeing humanity, how do you want to have relationship with us?"

As you can see, in exobiology there is no lack of humor. And as it is full of assumptions and hypotheses, and they do not get clear results, there are also those who think that real science is not. In this field, the limit of knowledge is marked by technology, imagination has no limits.

On an intense reflection
There is no denying, the subject has a philosophical side. Consequently, philosophers also have something to say on this subject, and it is also little wonder that scientists discover philosophy. From the base, exobiology seeks life outside the Earth. But what is life?
There is no problem in daily life to distinguish the living from the inanimate. But exobiologists work on the border between the two and need a precise definition of life. However, there is no universal definition. The definition includes concepts such as metabolism, growth, reproduction... At NASA, for example, they use the following definition of work: "Life is a chemical system that supports and maintains a vorical evolution".
Felix Olasagasti: "It is not possible to know exactly how life was born"
This young lasartearra works in the field of exobiology at the University of California. And it has taught us another vision of research.
Two terms are used: exobiology and astrobiology. Are they equivalent?
In fact yes. However, there is no precise definition to differentiate them. I think the decision to use one or the other has a commercial reason. Astrobiology is a concept created by the people of NASA that can take into account the origin of life on Earth more than exobiology, but not necessarily. For its part, ESA uses the term exobiology more.
There are many questions to answer, for example, how did life arise?
It is not possible to know exactly how the origin of life on Earth was, because one's life has lost its mark, but it is possible to say "that could be so." We can approach the moment the first genome appeared, since there is a subsequent record. But the previous story is lost and then we start from chemical approaches.
(Photo: N. N. Blacksmithing)
There is a leap: from biology down we get to one point and from chemistry to another, but there is a gap. We do not know everything from the first cell to the first genome.
Do you want to reach that first cell in your research?
It is one of the purposes of research. From my point of view there is no life without cells. In view of the laws of chemistry, one could make an approach to this cell through a system.
In my thesis I have studied the mathematical model of a system that is maintained. I have proposed an abstract reaction system, with the components that require a maintenance system. The membrane, for example, is critical in a living being and to maintain it needs a reaction network, to maintain it a source of energy is needed and overcome other problems. For example, in a membrane the substances cause osmotic pressure because the internal concentration is greater than the external one, and if it is very large the cell could explode. The cell must fix it.
Taking into account these concepts, I have raised the minimum elements that the system needs and a network of reaction, in abstract, I have determined mathematical equations and studied if it is kinetically stable.
(Photo: From archive)
So, don't you consider what life is made?
Although life is linked to matter, more than that is a process. This system that allows this process is the one that gives life. Note that in the definition they use in NASA no matter is mentioned (chemical system with Darwinian evolution).
Do you think you will find life outside the Earth?
I have the hope of finding life.
And intelligent life?
There may be intelligent life, but the probability is much lower. In any case, it is not something that concerns me especially.
Rementeria Argote, Nagore
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