Canadian and British astronomers have discovered the darkest planet in the Galaxy in the constellation Auriga, whose surface reflects only 0.6% of its star's light, according to an article accepted for publication in the Astrophysical Journal Letters.
“This albedo level is extremely low for any celestial body, and it suggests that this planet is blacker than new asphalt. This discovery suggests that we still have a lot to learn about WASP-12b and other similar exoplanets,”said Taylor Bell, an astronomer at McGill University in Montreal, Canada.
Over the past ten years, astronomers have discovered thousands of planets outside the solar system, some of which turned out to be similar in size to the Earth, and others - to smaller or enlarged copies of Jupiter. Now planetary scientists are actively working to study their atmosphere to assess whether life can exist on them, and to reveal the history of formation.
Great advances in this direction have been achieved in the study of "hot Jupiters" - the largest and most convenient for studying planets outside the solar system. Their hot atmosphere turned out to be similar in composition to the shells of gas of Jupiter and Saturn, mainly consisting of hydrogen, helium and hydrocarbons, and in their skies astronomers have discovered exotic glass and lead clouds and rain of precious stones.
Some "hot Jupiters," Bell says, would be nearly invisible to the human eye due to the fact that their atmosphere is filled with vast amounts of alkali metal ions and other elements that absorb visible light and convert it into heat and other forms of radiation. The most unusual representative of such planets was the "twin" of Jupiter WASP-12b, located in the constellation Auriga at a distance of about 1400 light years from Earth.
This planet was discovered in 2008 and since then, thanks to record-high surface temperatures, a short "year" that lasts only a day, and an unusual chemical composition, it has constantly attracted the attention of planetary scientists and astrophysicists. Over the past 10 years, scientists have found that the WASP-12 star "stretched" its companion, forcing the planet to turn into a kind of "egg", and gradually "blows away" its atmosphere, warming it up to 2500 degrees Celsius.
The high temperatures of WASP-12b, Bell notes, have made it difficult for scientists to measure how much light and heat the gas giant's surface reflects. The first chance to do this appeared for astronomers in October last year, when a total "planetary eclipse" occurred in this star system - the gas giant completely disappeared behind the disc of a yellow dwarf, around which it revolves.
When this happens, the overall brightness of the system decreases, allowing scientists to measure the planet's albedo by comparing the strength of the star's glow before and after the start of an eclipse. Such measurements are extremely difficult to carry out, since even the brightest planets are extremely weak light sources compared to the dimmest and coldest luminaries.
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Analyzing the images from the Hubble, Bell and his colleagues could not believe their eyes - the initial measurements showed that the strength of the WASP-12 glow did not actually change during the eclipse. After re-examining the data, scientists came to the conclusion that "hot Jupiter" is almost completely black - it reflects only 0.6% of the light falling on it. In reality, this indicator may be even lower, since the measurement error was quite high due to the imperfection of the space observatory instruments.
How exactly the planet manages to remain coal black, astronomers do not yet know, since clouds of alkali metals cannot form on it due to ultra-high temperatures in the upper atmosphere. Revealing its composition, according to scientists, could bring us closer to solving this riddle and understanding where the border between planets, brown dwarfs and stars lies.