The so-called warm Jovian planets are among the strangest of all. They are gas giants that revolve around the star much closer than, for example, Jupiter, and because of this, they have a much higher surface temperature. Now researchers have looked more closely at the atmosphere of the planet KELT-9b, one of the warm Jovians with the hottest atmosphere ever.
The new observations confirm the strangeness of this type of planet. The planet has a mass of almost three times that of Jupiter and orbits around its star, about 670 light-years away from us, so close that it takes only a day and a half to make a complete revolution, the one that the Earth makes in a year around the Sun. For this reason, the planet is “stuck”: it always has only one face facing the star while on the opposite side there is eternal night.
Using data from the Spitzer Space Telescope, the researchers realized that the heat of the atmosphere on the “diurnal” side of this planet is so high that even the molecules can’t remain intact. For example, hydrogen gas molecules are torn apart and are unable to reform until the atoms that make them up are on the “night” side. On this side, the slightly lower temperature allows these atoms to reform the molecules.
The dayside has such an extreme temperature that these planets are the only ones with such characteristics, as the researchers explain in their study published in Astrophysical Journal Letters. KELT-9b was discovered in 2017 thanks to Kilodegree Extremely Little Telescope (KELT), a program that used two robotic telescopes, one from Arizona and another from South Africa.
An interesting characteristic of this planet is that the temperature on its nightside was barely lower than the temperature on its dayside. This represented a characteristic that surprised the researchers themselves because usually such planets, which always have the same side facing the star, present considerable differences in temperature between one side and the other, something that does not appear in this case. Probably there is a continuous flow of heat that, thanks to strong winds, is constantly facing the dayside towards the night side.