What does space look like?
On a clear and cloudless night, we can see the stars on the black curtain overhead. In the photos returned by the astronomical telescope, in the endless darkness, the huge and dazzling planet for humans is like grains of gray dust, and the space is like a vast black and uninhabited desert.
This is not the case in science fiction movies. Space is full of diverse lives and civilizations. There are high-IQ creatures on many planets in “Star Wars”, but their appearance is very different from that of people on earth. Humanoid creatures with triangular heads and golden eyes; slugs without eyes and mucus all over their bodies; those with periscopes on their heads Snakes and so on. The aborigines of Pandora, the alien planet in “Avatar”, are blue-skinned humanoid creatures about 3 meters high. They are called the Na’vi people by the earth people and have the ability to communicate with plants and animals.
Is space a lifeless desert or a large vibrant garden? Although we have not found traces of living life in space so far, many scientists still believe with confidence that the answer should be the latter.
Different environments, different creatures
Life on Earth is the result of billions of years of adapting to the environment, development and evolution, and life on other planets should be the same. Therefore, in the imagination of scientists, life on other planets and life on Earth will be very different in appearance.
Let us first look at the orbit of the planet. In 2016, Chinese scientists calculated the measurement data of the Guo Shoujing telescope and Kepler satellites and found that about 80% of the extrasolar planets have orbits similar to those of the solar system planets, mostly near circular orbits with an eccentricity of less than 0.1, only about 20% The eccentricity of the exoplanet of, with an average value greater than 0.3, presents an obvious elliptical orbit. This result is exciting, because planets in a near circular orbit will not get too close to or distant from their stars at any time, and the temperature will be more stable and comfortable, and more suitable for nurturing life. Eighty percent of the planet’s orbit is nearly circular, which greatly enhances scientists’ confidence in searching for extraterrestrial life. On such planets, there may be creatures similar to those on Earth.
However, even for planets with long and narrow orbits, such as HD 76920b, the planet with the largest orbital eccentricity discovered so far, its close time to the star is short, the summer is very hot, and a long cold winter will follow. The living environment of such a planet is very bad for earth creatures, but scientists have not given up hope. They optimistically imagine that maybe there will be walking plants with limbs and leaves on such a planet. The walking plants are covered with green leaves, but they have animal limbs and can move flexibly. In the afternoon with sufficient sunlight, it will quietly bathe in sunlight for photosynthesis, and when resources are tight, its limbs can help them compete and seize survival materials. In hot summers and cold winters, they will escape to areas with suitable temperatures, or they may live through the winter with long sleep. When the planet approaches and leaves the star, there will be two short periods of suitable temperature. At this time, walking plants can seize the time to blossom and bear fruit and reproduce their offspring.
If you want to find similar creatures on the earth, it may be the green leaf sea slug or the snail worm. The former is a kind of snail, and the latter is a ciliate. They survive by swallowing algae, but they do not completely digest the algae. Instead, they incorporate the chloroplasts of the algae into their own cells and perform photosynthesis on their own, so that they have the ability of plants and animals at the same time.
The gravitational force of the stars on the planets will also affect the “children” born by the planets. Planets that are too close to the star will be affected by the strong gravitational force of the star, making the planet move in a fixed orbit. In this orbit, the rotation period of the planet is the same as the period it revolves around the star, which causes the planet to always face the star in the same hemisphere, just as we always see the same side of the moon on the earth. One side of such a planet is always bathed in sunlight, and the other side is plunged into eternal darkness, and different creatures will live on different sides. Photosynthesis is carried out on the light side, and organisms similar to desert plants on earth can live here. The backlit side is cold and dark. There may be animals covered in fur and sleepless. They open their mouths to “welcome” the lost animals from the Xiangyang side.
The gravitational force on planets that are too far away from the star is too weak. When affected by the gravitational force of a star in another galaxy, it is likely to deviate from its original orbit and become a lone wanderer in the universe. There are as many as 25 billion such “wanderers” in the universe. In the process of wandering, it is difficult for a planet to enjoy the light and heat of a star anymore, but maybe it is not a cold “dead star”. Its core may undergo elemental decay reactions or undergo violent geological activities. The life of the planet provides energy. But these beings will have to adapt to the environment without sunlight, just like the nitrifying bacteria, sulfur bacteria and iron bacteria in the rock and ocean depths of the earth, even without sunlight, they can also use chemical energy synthesis to oxidize inorganic substances and use them. The energy released by the oxidation process synthesizes carbon dioxide and water into organic matter to sustain life. However, the energy produced in this way is limited, and it can only meet the needs of the survival of miniature creatures, so most of the life in the dark star has a miniature size.
Walking plants live on a planet with both ice and fire (imaginary picture)
Internal conditions determine “appearance”
In addition to the planet’s orbit and stellar gravity, the internal conditions of the planet also affect the shape of living things.
For example, whether it is a gaseous planet or a solid planet, this can determine whether the creature is as light as a swallow or as strong as a cow. Animals and plants on gaseous planets like Saturn and Jupiter can obtain huge buoyancy, and they all “swim” in the atmosphere. Because of the lower gravity, the trees there can grow up to 10 times the height of the trees on the earth. Animals will “fly” in the air with airbags filled with hydrogen or methane, and enjoy the green algae clouds and balloon-like plants floating on the heights. And octopus-like animals.
When the ability to fly becomes a necessary skill for living things, the oxygen supply capacity of the muscles will determine whether the animal can hunt or escape for a long time. Most animals on the earth use the iron atoms in hemoglobin to combine and transport oxygen, but cephalopods such as octopuses use copper atoms in hemocyanin to transport oxygen. Compared with iron atoms, copper atoms The speed of combining oxygen is slower, but it can combine more oxygen, which makes the octopus slow to move but can move for a long time. For long-term flight, perhaps creatures on gaseous planets will abandon the red hemoglobin, and their blood will be blue-purple.
We know that life on earth originated from the ocean, so we have always believed that water is a necessary condition for the existence of life. Under the surface of Jupiter’s moon Ganymede, scientists have discovered a huge layered ocean whose total amount of seawater is much larger than that of the earth. There must be many alien creatures we dream of hiding here. The high core temperature of Ganymede makes the ice near the core melt into water, but the entire ice cannot be melted. The ice close to the surface is affected by Jupiter’s gravity and breaks and melts, so the ocean is divided into a layer of ice and water. The “sandwich” structure. If there is life in this layered ocean, they are likely to originate on the seabed, slowly invading layer by layer, forming a vertical ecosystem with a common origin. From the outside, this ecosystem is like a huge old tree. The “roots” at the bottom may be composed of countless amoeba cells, and the “trunks” and “branches” extending to the upper level are occupied by carnivores such as shrimps, crabs, fish, etc.
But must the liquid in the ocean be water? Will other liquid environments produce life? Scientists think it is possible. Saturn’s moon Titan looks very much like the earth. Its rivers and lakes are filled with liquids, but these liquids are very different from the water on the earth. This is liquid methane, the main component of fuel natural gas. A team of scientists from the United States and Mexico discovered a methane-based ecosystem in Mexico’s Yucatan Peninsula, where microorganisms depend on methane to survive, and other animals feed on methane microorganisms. Since there are methane microorganisms on the earth, other planets may also exist.
Imagination may come true
Although the above-mentioned life still exists only in the imagination of scientists, now we have found some evidence for the existence of creatures different from life on earth.
“Octopus” may be bred in gaseous planets
Titan, the largest satellite of Saturn, data from NASA’s Huygens probe shows that Titan contains many organic components related to the origin of life similar to the earth, such as nitrogen, methane and other hydrocarbons. Composed of a thick atmosphere. But unfortunately, the average temperature of Titan is -187℃, there is little liquid water, and the lake is basically liquid methane. Although there are also methane microorganisms on the earth, they will definitely not survive on the more severely cold Titan.
Can the methane microorganisms survive in Titan’s methane lakes? The available evidence gives scientists full confidence in this.
In 2017, NASA’s Cassini spacecraft detected the presence of two compounds on Titan. Their discovery made scientists more convinced that Titan can nurture life. A compound called acrylonitrile was found in the upper atmosphere of Titan. This compound can form a stable membrane structure similar to cell membranes in the cryogenic methane in the laboratory. And another compound called carbon chain anion was found to exist in Titan’s ionosphere. It is the “seed” that can grow into more complex organic particles. It is used as a starting point to continue chemical reactions. There may be organic life forms.
Coincidentally, the “Cassini” spacecraft also discovered the possibility of life on Enceladus. In 2015, NASA analyzed samples collected by Cassini on Enceladus and found large and complex organic molecules with molecular masses exceeding 200 relative atomic masses (1/12 of the mass of a 12C atom). As a standard, the ratio of the average atomic mass of any kind of atom to 1/12 of the mass of a 12C atom is called the relative atomic mass of the atom. It is composed of long carbon chains and carbon rings. This means that Enceladus can undergo complex biochemical processes, and such biochemical processes were also going on at the beginning of life on Earth.
In early 2017, “Cassini” also detected hydrogen molecules on the surface of Enceladus. On the earth, the biochemical reaction process that produces hydrogen is unique to the microorganisms of deep-sea hydrothermal vents, and the entire surrounding ecosystem is powered by this process. Based on this, Hunter Waite, an atmospheric scientist at the Southwest Research Institute in the United States, speculated that the organic matter at Enceladus’s underground hydrothermal vents may have evolved into life forms, and hydrogen is produced by their chemical reactions.
At present, we cannot verify whether there are aliens in the above-mentioned satellites, but their biochemical environment is very similar to the environment in the early stage of life on Earth. This is the strongest support for scientists’ conjecture. And if microorganisms that rely on chemical energy synthesis actually exist, wouldn’t the possibility of other organisms’ survival greatly increase?
DNA makes us different
If alien creatures are really completely different from Earth creatures as scientists imagined, then what caused it? On the earth, we call the substance that determines the properties of organisms DNA. Let’s just call the thing that determines the properties of alien organisms as alien DNA. Scientists have made some bold conjectures about the difference between the two DNAs.
We already know that the DNA of earth creatures is composed of 4 kinds of small organic molecules called bases. They are named guanine, cytosine, adenine and thymine. Changing the sequence of bases can determine all of earth creatures. Traits. Is alien DNA also composed of four bases? What if it is not four, but six or eight? A research team led by American biochemical scientist Steven Benner produced some “alien DNA” in the laboratory.
Will alien DNA be DNA made up of 8 bases? (Green (natural base G), red (A), blue (C), yellow (T), cyan (synthetic base B), pink (S), purple (P), orange (Z))
Steven Benner’s research on synthetic DNA has a long history. As early as 2006, Benner’s team created two artificial bases called Z and P by adjusting the structure of natural bases. Later, they used the same method to obtain a pair of bases called S and B. Base pair.
In February 2019, Benner’s team combined their artificial bases with natural bases and created hundreds of synthetic DNA molecules. Synthetic DNA is indeed different from natural DNA. It cannot be copied, transcribed, and translated by the original enzymes of earth organisms. Benner’s team found a mutant RNA polymerase of the T7 bacteriophage and finally succeeded in the transcription of this synthetic DNA. Does this mean that the bases of extraterrestrial DNA are very likely to be very inconsistent with those of earth creatures, because they have their own bases and corresponding enzymes?
But the work of Benner’s team ends here. Another scientist did an experiment to transfer synthetic DNA into the genome of earth creatures to make new proteins.
The research team led by Floyd Romsberg of the Scripps Research Institute in the United States created new bases that were different from Benner’s team, and they were named X and Y. In May 2014, they inserted the synthetic DNA containing this pair of new bases into the E. coli genome for the first time. When E. coli divides and reproduces, these artificial bases are also successfully replicated and inherited into the offspring, and as long as sufficient artificial bases are provided, it can be inherited stably.
However, similar to Benner’s group, the original amino acid-carrying tRNA of E. coli does not work when it encounters artificial bases and cannot be translated. In order to solve this problem, they improved the tRNA and the amino acids it carried, and eventually the offspring of Escherichia coli produced some new types of proteins and became a “new species.”
Natural DNA can control the production of 20 kinds of amino acids, while 8-base DNA can control the production of 172 kinds of amino acids, and more types of proteins can be synthesized. If alien DNA is completely different from natural DNA, and the proteins produced are naturally very different, then it is entirely possible for aliens to grow “weird-shaped” and possess various peculiar abilities.
Perhaps we have never been alone, and space is full of life, but we are born differently, unable to recognize and communicate with each other. But our enthusiasm for exploring life on other planets has never diminished, and we look forward to breaking the barriers one day in the future and aliens Say Hi.