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American astronomers from the University of Wisconsin-Madison have identified the most promising type of planet for the search for extraterrestrial life. We are talking about worlds covered in oceans orbiting white dwarfs (the cores of extinct stars). The study was published in the scientific journal of the American Astronomical Society (AASJ).
According to experts, the brightness of the white dwarf is dim enough not to interfere with radiation observations of the planets in its system.
Meanwhile, finding life in systems where the star has gone dark would require that planets around white dwarfs somehow survive one of the final stages of a star’s life, when the star expands 100 times and becomes a red giant. During this phase, the star engulfs nearby worlds. A similar fate awaits Earth, but it will only happen in 5 billion years.
Even if the water planet escaped destruction, the star’s rapid growth would be accompanied by a loss of mass and a huge spike in brightness. This would heat up all worlds in the system, causing the oceans to evaporate. Astronomers have calculated that in order to conserve water, the planets would have to be five to six times farther from their stars than the Earth is from the Sun.
When the star eventually cools and becomes a white dwarf, the water on the distant planet will turn to ice. To keep it liquid, the world needs to be close to the extinct star. The orbit may change due to a phenomenon called tidal migration.
The team notes that their model combines many conditions, but does not seem impossible. Scientists intend to intensify the search for new white dwarfs in order to study the planets around them and search for life on them.
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