10 possible life forms

In search of extraterrestrial intelligence, scientists often getaccusations of “carbon chauvinism,” because they expect other life forms in the universe to be made up of the same biochemical building blocks that we are, building our searches accordingly. But life may well be different - and people are thinking about it - so let's explore ten possible biological and non-biological systems that expand the definition of "life."


  • 1 Methanogens
  • 2 Silicon Based Life
  • 3 Other biochemical options
  • 4 Memetic life
  • 5 XNA-based synthetic life
  • 6 Chromodynamics, weak nuclear interaction and gravitational life
  • 7 Life forms from dust and plasma
  • 8 Inorganic chemical cells
  • 9 von Neumann probes
  • 10 Gay Hypothesis


In 2005, Heather Smith of InternationalSpace University in Strasbourg and Chris Mackay of the Ames Research Center at NASA have prepared a paper examining the possibility of life based on methane, the so-called methanogens. Such life forms could consume hydrogen, acetylene, and ethane, exhaling methane instead of carbon dioxide.

This could make habitable zones in cold worlds like the moon of Saturn the Titan. Like Earth, the atmosphere of Titan is represented mostly by nitrogen, but mixed with methane. Titanium is also the only place in our solar system, except for the Earth, where there are large liquid bodies of water - lakes and rivers from an ethane-methane mixture. (Underground ponds are also present on Titan, its sister moon Enceladus, as well as on the satellite of Jupiter Europe). Liquid is considered necessary for the molecular interactions of organic life and, of course, the main focus will be on water, but ethane and methane also allow such interactions to take place.

NASA and ESA Cassini-Huygens Mission in 2004I watched a dirty world with a temperature of -179 degrees Celsius, where the water was solid as stone, and methane floated through river valleys and basins into polar lakes. In 2015, a team of chemical engineers and astronomers at Cornell University developed a theoretical cell membrane made from small organic nitrogen compounds that could function in liquid titanium methane. They called their theoretical cell “nitrogenosome,” which literally means “nitrogen body,” and it had the same stability and flexibility as the terrestrial liposome. The most interesting molecular compound was acrylonitrile nitrogenosome. Acrylonitrile, a colorless and poisonous organic molecule, is used for acrylic paints, rubber and thermoplastics on Earth; he was also found in the atmosphere of Titan.

The implications of these experiments for searchesextraterrestrial life is difficult to overestimate. Life could not only potentially develop on Titan, but it can also be detected by hydrogen, acetylene and ethane traces on the surface. Planets and moons, in whose atmospheres methane predominates, can be not only around stars like the Sun, but also around red dwarfs in the wider “Goldilocks zone”. If NASA launches the Titan Mare Explorer in 2016, already in 2023 we will receive detailed information about a possible life on nitrogen.

Silicon Based Life

Silicon-based life is perhaps the mosta common form of alternative biochemistry, beloved by popular science and science fiction - remember the Horta from Star Trek. This idea is far from new, its roots go back to the thoughts of Herbert Wells in 1894: “What a fantastic imagination could play out of this assumption: imagine silicon-aluminum organisms - or maybe silicon-aluminum people right away? “Who travel through the atmosphere from gaseous sulfur, let's put it this way, along the seas of liquid iron with a temperature of several thousand degrees, or something like that, just above the temperature of a blast furnace.”

Silicon remains popular precisely becausevery similar to carbon and can form four bonds, like carbon, which opens up the possibility of creating a biochemical system completely dependent on silicon. This is the most common element in the earth's crust, except for oxygen. There are algae on Earth that incorporate silicon into their growth process. Silicon plays a second role after carbon, since it can form more stable and diverse complex structures necessary for life. Carbon molecules include oxygen and nitrogen, which form incredibly strong bonds. Complex silicon-based molecules, unfortunately, tend to decay. In addition, carbon is extremely abundant in the universe and has existed for billions of years.

Silicon-based life is unlikely to appear inan environment similar to terrestrial, since most of the free silicon will be locked in volcanic and igneous rocks of silicate materials. It is believed that in a high-temperature environment, everything can be different, but no evidence has yet been found. An extreme world like Titanium could support silicon-based life, possibly coupled with methanogens, because silicon molecules like silanes and polysilanes can mimic the Earth’s organic chemistry. Nevertheless, carbon prevails on the surface of Titanium, while most of the silicon is deep below the surface.

NASA astrochemist Max Bernstein suggested thatsilicon-based life could exist on a very hot planet, with an atmosphere rich in hydrogen and poor in oxygen, allowing complex silane chemistry to occur with reverse silicon bonds with selenium or tellurium, but this, according to Bernstein, is unlikely. On Earth, such organisms would multiply very slowly, and our biochemistry would not interfere with each other. However, they could slowly eat our cities, but "they could use a jackhammer."

Other biochemical options

In principle, there were quite a few suggestionsregarding life systems based on something other than carbon. Like carbon and silicon, boron also tends to form strong covalent molecular compounds, forming different structural variants of hydride, in which boron atoms are connected by hydrogen bridges. Like carbon, boron can bind to nitrogen, forming compounds similar in chemical and physical properties to alkanes, the simplest organic compounds. The main problem with boron-based life is that it is a fairly rare element. Life based on boron will be most appropriate in an environment whose temperature is low enough for liquid ammonia, then chemical reactions will proceed more controlled.

Another possible life form that attractedsome attention, this is arsenic-based life. All life on Earth consists of carbon, hydrogen, oxygen, phosphorus and sulfur, but in 2010, NASA announced that it had discovered the bacterium GFAJ-1, which could include arsenic instead of phosphorus in the cell structure without any consequences for itself. GFAJ-1 lives in the arsenic-rich waters of Lake Mono in California. Arsenic is poisonous to any living creature on the planet, except for a few microorganisms that normally tolerate it or breathe it. GFAJ-1 was the first case when the body included this element as a biological building block. Independent experts diluted this statement a bit when they found no evidence of arsenic incorporation into DNA or at least some arsenates. Nevertheless, interest in a possible biochemistry based on arsenic flared up.

As a possible alternative to water forammonia was also advanced in the construction of life forms. Scientists have suggested the existence of biochemistry based on nitrogen-hydrogen compounds that use ammonia as a solvent; it could be used to create proteins, nucleic acids and polypeptides. Any ammonia-based life form must exist at low temperatures, at which ammonia takes on a liquid form. Solid ammonia is denser than liquid ammonia, so there is no way to stop it freezing during a cold snap. For unicellular organisms, this would not be a problem, but would cause chaos for multicellular organisms. Nevertheless, there is the possibility of the existence of unicellular ammonia organisms on the cold planets of the solar system, as well as on gas giants like Jupiter.

Sulfur is believed to have served as the basis for a start.metabolism on Earth, and well-known organisms whose metabolism includes sulfur instead of oxygen, exist in extreme conditions on Earth. Perhaps in another world, sulfur-based life forms could have gained an evolutionary advantage. Some believe that nitrogen and phosphorus could also take the place of carbon under rather specific conditions.

Memetic life

Richard Dawkins believes that the basic principle of lifeit sounds like this: "All life develops, thanks to the survival mechanisms of reproducing creatures." Life must be able to reproduce (with some assumptions) and reside in an environment where natural selection and evolution will be possible. In his book “The Selfish Gene,” Dawkins noted that concepts and ideas are developed in the brain and spread among people through communication. In many ways, it resembles the behavior and adaptation of genes, so he calls them "memes." Some compare the songs, jokes and rituals of human society with the first stages of organic life - free radicals floating in the ancient seas of the Earth. The creations of the mind are reproduced, evolving and fighting for survival in the realm of ideas.

Similar memes existed before humanity, insocial calls of birds and the learned behavior of primates. When mankind became able to think abstractly, memes were further developed by managing tribal relations and forming the basis for the first traditions, culture and religion. The invention of writing pushed the development of memes even more, as they were able to spread in space and time, transmitting memetic information similar to how genes transmit biological information. For some, this is a pure analogy, but others believe that memes represent a unique, albeit slightly rudimentary and limited form of life.

Some went even further. Georg van Dream developed the theory of "symbiosism", which implies that languages ​​are themselves life forms. Old linguistic theories considered the language a bit of a parasite, but van Dreem believes that we live in collaboration with the memetic entities that inhabit our brains. We live in symbiotic relationships with linguistic organisms: without us they cannot exist, and without them we are no different from monkeys. He believes that the illusion of consciousness and free will resulted from the interaction of animal instincts, hunger and lust of a human carrier and a linguistic symbiont, reproduced with the help of ideas and meanings.

XNA-based synthetic life

Life on Earth is based on two transportsinformation to molecules, DNA, and RNA, and for a long time, scientists pondered whether other similar molecules could be created. Although any polymer can store information, RNA and DNA display heredity, coding and transmission of genetic information and are able to adapt over time during evolution. DNA and RNA are chains of nucleotide molecules consisting of three chemical components - phosphate, a five-carbon sugar group (deoxyribose in DNA or ribose in RNA) and one of five standard bases (adenine, guanine, cytosine, thymine or uracil).

In 2012, a group of scientists from England, Belgium andDenmark was the first in the world to develop xenonucleic acid (KNA, XNA), synthetic nucleotides that functionally and structurally resemble DNA and RNA. They were developed by replacing the sugar groups of deoxyribose and ribose with various substitutes. Such molecules were made before, but for the first time in history they were able to reproduce and evolve. In DNA and RNA, replication occurs using polymerase molecules that can read, transcribe and reverse transcribe normal nucleic acid sequences. The group developed synthetic polymerases that created six new genetic systems: HNA, CeNA, LNA, ANA, FANA, and TNA.

One of the new genetic systems, HNA, orhexitonucleic acid was reliable enough to store the right amount of genetic information that could serve as the basis for biological systems. Another, threosonucleic acid, or TNA, was a potential candidate for the mysterious primary biochemistry that reigned at the dawn of life.

There are tons of potential uses for theseachievements. Further research can help develop better models for the emergence of life on Earth and will have implications for biological speculation. XNA can be used in therapeutic applications because nucleic acids can be created to treat and communicate with specific molecular targets that will not deteriorate as quickly as DNA or RNA. They can even form the basis of molecular machines or, in general, an artificial life form.

But before this becomes possible, there must bedeveloped other enzymes compatible with one of the XNA. Some of them have already been developed in the UK at the end of 2014. There is also the possibility that XNA can harm RNA / DNA organisms, so safety should come first.

Chromodynamics, weak nuclear interaction and gravitational life

In 1979, scientist and nanotechnologist RobertFreitas Jr suggested a possible non-biological life. He stated that a possible metabolism of living systems is based on four fundamental forces - electromagnetism, strong nuclear interaction (or quantum chromodynamics), weak nuclear interaction and gravity. Electromagnetic life is the standard biological life that we have on Earth.

Chromodynamic life could be based onstrong nuclear interaction, which is considered the strongest of the fundamental forces, but only at extremely short distances. Freitas suggested that such a medium could be possible on a neutron star, a heavy rotating object 10-20 kilometers in diameter with the mass of the star. With incredible density, a powerful magnetic field and gravity 100 billion times stronger than on Earth, such a star would have a core with a 3-km crust of crystalline iron. Under it would be a sea with incredibly hot neutrons, various nuclear particles, protons and atomic nuclei, and possible “neutron-rich” nuclei. In theory, these macronuclei could form large supernuclei similar to organic molecules; neutrons would act as the equivalent of water in a bizarre pseudobiological system.

Freitas saw life forms based on the weaknuclear interactions as unlikely, since weak forces act only in the subnuclear range and are not particularly strong. As beta-radioactive decay and free neutron decay often show, weak interaction life forms could exist with careful monitoring of weak interactions in their environment. Freitas introduced creatures made up of atoms with excess neutrons that become radioactive when they die. He also suggested that there are regions of the Universe where a weak nuclear force is stronger, which means that the chances of such a life appearing are higher.

Gravity beings can also exist,since gravity is the most common and effective fundamental force in the universe. Such creatures could receive energy from gravity itself, receiving unlimited power from collisions of black holes, galaxies, and other celestial objects; smaller creatures - from the rotation of planets; the smallest - from the energy of waterfalls, wind, tides and ocean currents, possibly earthquakes.

Life forms from dust and plasma

Organic life on Earth is based on molecules.with carbon compounds, and we have already figured out possible compounds for alternative forms. But in 2007, an international group of scientists led by V.N. organic chemistry. This behavior is also born in the state of plasma, the fourth state of matter after solid, liquid and gaseous, when electrons break away from atoms, leaving a mass of charged particles.

Tsytovich’s group found that when electroniccharges are separated and the plasma is polarized, particles in the plasma self-organize into spiral structures like a corkscrew, electrically charged, and are attracted to each other. They can also divide, forming copies of the original structures, like DNA, and induce charges in their neighbors. According to Tsytovich, “these complex, self-organizing plasma structures meet all the necessary requirements in order to consider them candidates for inorganic living matter. They are autonomous, they reproduce and they evolve. ”

Some skeptics believe that such statementsare more an attempt to attract attention than serious scientific claims. Although helical structures in plasma may resemble DNA, similarity in form does not necessarily imply similarity in function. Moreover, the fact that spirals reproduce does not mean life potential; clouds do that too. Even more depressing, most of the research has been done on computer models.

One of the participants in the experiment also reported thatalthough the results did resemble life, in the end, they were "just a special form of the plasma crystal." And yet, if inorganic particles in a plasma can grow into self-reproducing, evolving life forms, they may be the most common life form in the Universe, thanks to the ubiquitous plasma and interstellar dust clouds all over space.

Inorganic chemical cells

Professor Lee Cronin, chemist at the College of Science andengineering at the University of Glasgow, dreams of creating living cells from metal. He uses polyoxometallates, a series of metal atoms bonded to oxygen and phosphorus, to create cell-like bubbles, which he calls “inorganic chemical cells”, or iCHELLs (this acronym can be translated as “non-ovlet”).

Cronin's group began by creating salts fromnegatively charged ions of large metal oxides associated with a small positively charged ion like hydrogen or sodium. A solution of these salts is then injected into another saline solution full of large positively charged organic ions associated with small negatively charged ones. Two salts meet and exchange parts, so that large metal oxides become partners with large organic ions, forming something like a bubble that is impervious to water. By changing the backbone of metal oxide, it is possible to achieve that the bubbles acquire the properties of biological cell membranes, which selectively pass and release chemicals from the cell, which can potentially allow the same type of controlled chemical reactions to occur in living cells.

A group of scientists also made bubbles in the bubbles,mimicking the internal structures of biological cells, and has made progress in creating an artificial form of photosynthesis, which could potentially be used to create artificial plant cells. Other synthetic biologists note that such cells can never become alive until they get a replication and evolution system like DNA. Cronin does not lose hope that further development will bear fruit. Among the possible applications of this technology there is also the development of materials for solar fuel devices and, of course, medicine.

According to Cronin, “the main goal is to createcomplex chemical cells with living properties that can help us understand the development of life and go the same way to bring new technologies based on evolution into the material world - a kind of inorganic living technology. "

Von Neumann probes

Machine-based artificial life isa fairly common idea, almost banal, so let's just look at von Neumann's probes so as not to bypass it. They were first invented in the mid-20th century by the Hungarian mathematician and futurologist John von Neumann, who believed that in order to reproduce the functions of the human brain, a machine must have self-healing and self-healing mechanisms. So he came up with the idea of ​​creating self-reproducing machines, which are based on observations of the increasing complexity of life in the process of reproduction. He believed that such machines could become a kind of universal designer, which could not only create complete replicas of himself, but also improve or change versions, thereby realizing evolution and increasing complexity over time.

Other futurologists like Freeman Dyson and EricDrexler quickly applied these ideas to the field of space research and created a von Neumann probe. Sending a self-reproducing robot into space may be the most efficient way to colonize a galaxy, because you can capture the entire Milky Way in less than one million years, even if it is limited by the speed of light.

As Michio Kaku explained:

“Von Neumann probe is a robot designedto reach distant star systems and create factories that will build copies of themselves by thousands. A dead moon, not even a planet, can be an ideal destination for von Neumann probes, since it will be easier to land and take off from these moons, and also because there is no erosion on the moons. The probes could live off the land, mining iron, nickel and other raw materials for the construction of robotic factories. They would create thousands of copies of themselves, which would then disperse in search of other stellar systems. "

Over the years, various versions have been invented.the basic idea of ​​the von Neumann probe, including exploration and reconnaissance probes for quiet research and observation of extraterrestrial civilizations; communication probes scattered throughout the cosmos to better capture the radio signals of aliens; work probes for the construction of supermassive space structures; colonization probes that will conquer other worlds. There may even be guiding probes that will launch young civilizations into space. Alas, there may be berserker probes whose task is to destroy the traces of any organic matter in space, followed by the construction of police probes that will repel these attacks. Given that von Neumann probes can become a kind of cosmic virus, we should carefully approach their development.

Gay Hypothesis

In 1975, James Lovelock and Sidney Upton jointlywrote an article for New Scientist titled "Finding Gays." Adhering to the traditional point of view that life originated on Earth and flourished due to the necessary material conditions, Lovelock and Upton suggested that life thus took an active role in maintaining and determining the conditions for its survival. They suggested that all living matter on Earth, in the air, oceans, and on the surface is part of a single system that behaves like a superorganism that can adjust the temperature on the surface and the composition of the atmosphere in a way that is necessary for survival. They named this system Gaia, in honor of the Greek goddess of the earth. It exists to maintain homeostasis, through which the biosphere can exist on earth.

Lovelock has been working on the Gaia hypothesis since the mid-60s.years. The basic idea is that the Earth’s biosphere has a number of natural cycles, and when one goes awry, the others compensate for it in such a way as to maintain vitality. This might explain why the atmosphere is not entirely carbon dioxide or why the seas are not too salty. Although volcanic eruptions made the early atmosphere primarily composed of carbon dioxide, nitrogen-producing bacteria and plants that produced oxygen during photosynthesis appeared. Millions of years later, the atmosphere has changed in our favor. Although rivers transport salt to the oceans from rocks, the salinity of the oceans remains stable at 3.4% as salt seeps through cracks in the ocean floor. These are not conscious processes, but the result of feedback that keeps the planets in habitable balance.

Other evidence includes that if not forbiotic activity, methane and hydrogen would disappear from the atmosphere in just a few decades. In addition, despite a 30% increase in the temperature of the Sun over the past 3.5 billion years, the average global temperature has staggered by only 5 degrees Celsius, thanks to a regulatory mechanism that removes carbon dioxide from the atmosphere and locks it in fossilized organic matter.

Lovelock's initial ideas were mettaunts and accusations. Over time, however, Gaia’s hypothesis influenced ideas about the Earth’s biosphere and helped shape their whole perception in the scientific world. Today, Gaia’s hypothesis is more respected than accepted by scientists. It is rather a positive cultural framework in which scientific research should be carried out on the topic of the Earth as a global ecosystem.

Paleontologist Peter Ward has developed a competitiveMedea’s hypothesis, named after the mother who killed her children, in Greek mythology, the main idea of ​​which is that life inherently seeks self-destruction and suicide. He points out that historically most of the mass extinctions have been caused by life forms, such as microorganisms or hominids in pants, which cause severe damage to the Earth’s atmosphere.

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