(ORDO NEWS) — The TESS exoplanet hunter discovered the youngest hot Jupiter, only 17 million years old. These red-hot gas giants are dangerously close to their star – some make a complete revolution around her in just a few hours. There are no such exotic objects in the Solar system, but in the Galaxy, as it turned out, there is enough.
In 1995, astronomers from Switzerland discovered the first planet in another stellar system – the same as the Sun, a yellow dwarf in the constellation Pegasus. At first they thought that it was similar to the Earth, but soon realized: the planet 51 Pegasus is closer to its star than even Mercury. The circulation period is only four days. The mass is half Jupiter, and the size is probably much larger. In fact, a gigantic burning gas ball.
“It was a shock. Previously, it was believed that other planetary systems are similar to ours. Our giant gas planets are very far from the Sun. For comparison: Jupiter has a circulation period of more than four thousand days. And here it’s only four! Because of the proximity the temperature on the surface there reaches a thousand degrees to the parent star. Then they are still the same. Now there are about five hundred out of four thousand open exoplanets, “says Valery Shematovich, head of the solar system research department of the Institute of Astronomy RAS (INASAN).
Hot Jupiters were named after the largest planet in the solar system. According to modern concepts, such giants form behind the line of snows – where gas and water condense. We have this border between Mars and Jupiter. Why is this rule not valid for his ardent distant fellows?
“According to the main hypothesis, they migrated. The big question is why. Perhaps several giant planets formed on the outskirts begin to move due to resonant interaction. Another mechanism is braking in the residual gas-dust cloud. In favor of migration, a number of hot jupiters is in elliptical, elongated orbits. Sometimes they are strongly inclined to the ecliptic plane. Subsequently, due to tidal action, the stars of the orbit become circular, “the scientist explains.
A few years ago, Switzerland proposed a model for the formation of hot Jupiters: a compaction of matter occurs and attracts gas and dust falling on a star.
“In principle, such a scenario is possible, but so far it has many uncertain parameters that need to be clarified,” Valery Simatovich notes.
The strangest atmosphere
Giant hot Jupiters are the largest of the exoplanets. They were discovered first, because with their mass they perturbed the orbit of the parent star. Her pulsation could not explain this, there was only one option – a planet nearby.
Another observation method is the passage of a planet through a star’s disk (transit). Scientists for a long time could not understand why, when hot Jupiter only approaches the disk, but does not overlap it, the brightness of the star decreases. Most likely, the planet has a gas shell of hydrogen, the edge of which is the first to crawl onto the disk. Thanks to such eclipses, it was possible to consider the structure and study the properties of exotic atmospheres.
In about a quarter of them, the gas shells are elongated. In theory, hot Jupiters should eventually dump gas on a star and die. But since these are giant planets, strong gravity and gas reserves in the atmosphere, despite the high rate of its loss, provide a sufficiently long life time. Perhaps hot jupiters have silicate or iron nuclei – this cannot yet be verified.
In Russia, the gas shells of hot Jupiters are engaged in a scientific group at INASAN led by Director Dmitry Bisikalo. Scientists have gained extensive experience modeling the atmospheres of Jupiter and Saturn, and this is now useful for the study of exoplanets. In 2019, a laboratory was established there to study Stars with Exoplanets under a government grant. It was headed by a leading specialist in spectroscopy of stellar atmospheres, professor at Uppsala University Nikolai Piskunov.
“Hot Jupiters are extremely important for testing modern theories of the formation of planetary systems. In the future, everything that we develop for their study will be applied to sub-neptunes and super-earths. The main task is to find planets in the habitable zone of stellar systems. Statistics claim that they exist. Then in their atmospheres we will look for biomarkers of life,” Simatovich lists.
Hopes are pinned on new instruments, because hot Jupiters, unlike other exoplanets, are easier to observe – they are huge and close to the star. And this gives many times more opportunities for testing hypotheses and models. Next year, they plan to launch into orbit the NASA space observatory, James Webb, and in 2024, the Russian Spectrum-UV telescope, the successor to the Spektr-RG successfully operating in space.
Hot Jupiters also study from Earth – for example, using ALMA radio telescopes in Chile. In Russia, new spectrographs for this purpose will soon be installed on small telescopes in Simeiz in the Crimea and at the peak of Terskol in the Caucasus.
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