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To discover and confirm the presence of a planet around other stars than the sun, astronomers expect to have completed three orbits. However, this very effective technique has its drawbacks because it does not confirm the presence of planets at relatively long periods (it is ideally suited for periods of a few days to a few months). To overcome this obstacle, a team of astronomers under the direction of the University of Geneva (UNIGE) has developed a method that ensures the presence of a planet in a few months, even if it takes 10 years to encircle its star: This new method is described for the first time in the journal Astronomy & Astrophysics .
The method of transits, consisting of detecting a drop in the luminosity of the host star at the moment of the passage of the planet, is very effective in finding exoplanets. It allows to estimate the radius of the planet, the inclination of the orbit and can be applied to a large number of stars at the same time. However, it has a significant limitation: since it is necessary to wait at least three passages in front of the star to confirm the existence of a planet, it is currently only appropriate to detect planets with short orbital periods (typically from a few days to a few months). Astronomers should wait more than 30 years to detect a planet similar to Jupiter that needs 11 years to go around.
To overcome this obstacle, an astronomical team led by researcher Helen Giles, of the Department of Astronomy of the UNIGE Faculty of Science and a member of the NCCR PlanetS, developed a original method. In analyzing data from the K2 space telescope, a star showed a significant temporary decay in brightness, the signature of a possible transit, ie the passage of a planet in front of its star. "We had to analyze hundreds of light curves," says the astronomer, to find one where such transit was unequivocal
Helen Giles consulted recent data from the Gaia mission to determine the diameter of the Referenced star EPIC248847494 and its distance, 1500 light-years from the planet Earth. With this knowledge and the fact that the transit lasted 53 hours, she found that the planet is 4.5 times the distance between the sun and the Earth, and so it takes about 10 years to orbit a time. The key question that had to be answered was whether it was a planet and not a star. The Euler telescope of UNIGE in Chile would provide the answer. By measuring the radial velocity of the star, which allows to deduce the mass of the planet, she was able to show that the mass of the object is less than 13 times that of Jupiter, well below the minimum mass of a star ("This technique could be used to chase living planets resembling the Earth around stars like the sun," says Helen Giles, "we have already found Earths around 39; red dwarf stars whose stellar star is close to that of Jupiter. "The radiation can have consequences on life that are not exactly known." With its method, it will no longer be necessary to d & # 39; wait several years to find out if the only transit detected is due to the presence of a planet. "In the future, we could even see if the planet has one or more moons, like our Jupiter," she concludes.
Learn more:
Japanese astronomers discover giant gaseous planets orbiting evolved stars
More information:
The longest period transiting the candidate planet of K2. arxiv.org/abs/1806.08757
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