There are many wandering planets in the universe. Wandering planets are sometimes called “galactic wanderers” or “orphan planets”. These cold, dark planets travel alone in space and have no stars to “rely on”. In fact, a long time ago, at the beginning of their formation, they revolved around a certain star, but they were later thrown out, which can be said to be “abandoned by their parents”. Astronomers estimate that there may be billions of wandering planets in the Milky Way—with a ratio of at least 1:1 to stars.
It seems futile to find life on these cold, desolate planets, but in the past 20 years, astronomers have put forward many possible scenarios. They believe that life may also appear on planets that do not orbit stars—as long as they are suitable. Under the conditions, plus a little luck…
The famous American astronomer and astrophysicist Frank Drake proposed an equation named after himself in 1961 to estimate how many extraterrestrial civilizations may exist in the Milky Way. , The emergence of this equation is generally regarded as the beginning of a new era in the search for extraterrestrial intelligent life. But a few decades later, Frank Drake admitted that his estimate was too conservative, because he believed that not only the extraterrestrial planets orbiting stars may have life, but also the wandering planets.
Beyond the habitable zone
The distance between the sun and the earth
For a planet to nurture life, it first needs to have two important conditions-one is a certain liquid solvent, which helps to transport minerals and other substances that are vital to life between cells; the other is that organisms can obtain it. The source of energy, so that it can continue to survive and grow.
The earth is close enough to the star, an ocean with liquid water (to meet solvent requirements), and a source of visible light that can ensure sufficient photosynthesis (to meet energy requirements). If the earth is too close to the sun, the light will be too strong and the sea water will boil; if the earth is too far from the sun, the ocean will freeze, and it will be difficult for plants to obtain enough light energy to convert into chemical energy. In fact, the position of the earth is perfect: it is neither too hot nor too cold, just in what astronomers call the “habitable zone” or “habitable zone”. Such a planet is a paradise for living organisms.
For a long time, when scientists search for extraterrestrial life, they have always focused on habitable planets like the Earth; those that orbit stars but are outside the traditional habitable zone; or those that may have different biochemistry from the Earth. Characteristic planet. However, some scholars believe that such a strategy limits the search range-why does this planet orbit the star? If this is a wandering planet, is it possible that it has life components?
In 2019, a paper published in the International Journal of Astrobiology analyzed the possibility of life in the ocean beneath the outer ice layer of wandering planets. The article believes that if a terrestrial planet is thrown out of the orbit of its star, an outer layer of ice will be formed, and the cold of interstellar space will prevent the ocean from being completely liquid. However, the ice layer can also isolate the inside of the planet from the cold external environment, as if covering the planet with a blanket. In the depths of the planet’s core, radioactive elements will continue to generate heat, warming it from the inside out.
This combination of external insulation and internal heating may protect the oceans of wandering planets from freezing. For example, if the current earth is thrown out of the solar system, its own radioactive material content may not be enough to prevent the ocean from freezing, and the earth may not have enough water or geothermal activity to ensure the survival of life. However, scientists believe that if the earth is thrown out of the solar system shortly after its formation, there will be more geothermal activity in the core at that time, and the ocean of liquid water may continue to exist.
In addition, in a few other cases, the wandering planet can still maintain the temperature of liquid water-if the wandering planet has a dense hydrogen atmosphere, it will act as a blanket and even allow liquid to exist on the surface of the planet. , Rather than under a thick layer of ice; or, if a planet is thrown from the orbit of a star, and it has a satellite attached to it, then the satellite can remain in the friction caused by the planet’s tidal force warmth.
In the centers of some very active galaxies, there are supermassive black holes. When matter falls into the black hole, it will emit strong radiation.
Therefore, on the wandering planet, the need for solvents may be met. But there is also a missing factor, that is, where liquid water may be available, where does the energy for the organism’s metabolism come from? Where do they get the energy to sustain themselves?
For this reason, astronomers envisioned an unlikely source of energy.
In the centers of some very active galaxies, there are supermassive black holes. When matter falls into the black hole, it will emit strong radiation. If the wandering planet is close to the core of this active galaxy, the radiation emitted by the black hole can be used to provide energy for photosynthesis.
When this radiation produces photosynthesis, there is a balance between the damage of extreme ultraviolet rays to cells. The seawater, which is several meters deep on the surface of the soil or planet, can be used as a barrier to protect life underground or in the ocean from ultraviolet radiation, while allowing enough visible light to pass through to promote photosynthesis. Scientists believe that an active galactic nucleus (supermassive black hole) may be able to support the emergence of life on a wandering planet less than 1,000 light-years from the center of the galaxy (by comparison, the Earth is 25,000 light-years from the center of the Milky Way).
What would life be like on such a wandering planet? You can imagine that they will be larger than microbes, but perhaps not as complicated as the most complex creatures we have seen on earth. There, we may not see dolphins, or any similar advanced species.
However, even if all the above conditions are met, whether we can detect signs of life on extraterrestrial planets in the near future is still an open question, and it is even more difficult for wandering planets, because astronomers cannot study typical exoplanets like a typical exoplanet. , Using the light from the parent star as a possible sign of life. But even on the earth, we are still amazed by the ability of extremophiles to survive in the harshest corners of the environment; then in the dark and cold interstellar space, on a wandering planet, why can’t the same extreme life appear?