The search for extraterrestrial life focuses on exoplanets, such as Kepler-186f, orbiting the M-class star in the habitable zone. However, not all of these “zones” are formed equal. Some planets are too close to the stars and receive a dangerous portion of radiation.
On January 9, 1992, scientists reported an important discovery. At a distance of 2,300 light-years from the Sun, two planets rotate, called Poltergeist and Draugr. They became the first confirmed exoplanets - worlds outside our system. Now in the list of foreign worlds there are 3,728 planets in 2795 systems. And for each of us is ready the question: "Is there anyone alive?".
For decades, astronomers have been trying to find signs of life on exoplanets. First of all, they were interested in the presence of water. However, Michael Mendillo of Boston University is considering another idea. In a recent article, he suggested studying the ionosphere of a foreign world more closely. You just need to find such as on Earth, that is, filled with single oxygen ions.
The work of the scientist began after receiving a grant from the National Science Foundation, which allows to compare all the planetary ionospheres in the solar system. The team also collaborated with NASA's MAVEN mission, trying to understand how molecules in the Martian ionosphere managed to escape from the planet. It has long been known that the planetary ionospheres are different, so the researchers decided to understand why the earth was so lucky. While the ionospheres of foreign worlds are filled with complex charged molecules created from carbon dioxide and hydrogen, the Earth fills everything with oxygen. And this is a special kind of - single atoms with a positive charge.
The team had to cross out various options until the main suspects appeared - green plants and algae. It's all about atomic oxygen, whose origin can be traced to photosynthesis. Now you need to find a criterion by which the ionosphere can become a biomarker that points to real life.
10-minute infrared representation of the Earth, obtained by the Apollo 16 mission. Bright yellow color - “day” of atomic oxygen (O). On the dark side near the equator, bands of the “night sky” are visible, appearing from atomic oxygen ions (O +) in the ionosphere
Most solar planets have some oxygen in the lower atmospheric layers. But at the Earth level reaches 21%. The reason is that a huge number of organisms are engaged in the transformation of light, water and carbon dioxide into sugar and oxygen. This is photosynthesis, lasting 3.8 billion years.
If you destroy all the plants, the oxygen will disappear from the earth's atmosphere after thousands of years. Excess oxygen molecules in the form of O 2 rise up. At an altitude of 150 km, UV light divides it into two parts. Single atoms rise into the ionosphere, where even more UV light and X-rays detach electrons from the outer shells, leaving charged oxygen. The abundance of O 2 near the earth's surface creates an abundance of O + at height. Mendillo believes that this idea will significantly narrow the search. Yes, we know that water is needed, but no one really knows how much it should be. Would we have just enough of the Mediterranean? Or enough of the Pacific? However, the ionosphere provides more specific answers. Just need to understand: the maximum electron density associated with oxygen ions, which allows access to photosynthesis and life.
Of course, scientists do not forget about other components, like the right temperature, the presence of a magnetic field, etc. But Mendillo believes that the ionosphere will be an excellent starting point. He also says that in 10 years we will be able to have the necessary search technology.