In the white-hot atmosphere of this exoplanet called KELT-9b, even the molecules are torn apart.
Massive gas giants called "hot Jupiters" - planets that orbit too close to their parent star for life on their surface - are some of the most unusual worlds outside the solar system. New observations show that the hottest of these planets contain ionized gas in the atmosphere - that is, a gas whose molecules, when exposed to high temperatures, dissociate into atoms.
This planet, called KELT-9b, is a super-hot, hot Jupiter about three times the mass of the largest planet in the solar system, orbiting a star about 670 light-years away. This planet - whose surface temperature reaches 4300 degrees Celsius (which is more than even the temperature of some stars) is the hottest planet ever discovered by scientists until today. The proximity of the planet to the star determines its synchronous rotation - in other words, the planet KELT-9b always faces the parent star with the same side, called the day side, while the other, night side of the planet remains in eternal shadow.
In the new study, a team of astronomers led by Megan Mansfield, a graduate student at the University of Chicago, USA, used NASA's Spitzer space telescope to observe the planet KELT-9b. The observations made by the team showed that the thermal regime on the planet causes the dissociation of hydrogen molecules on the day side of the planet, while on the night side there is a recombination of particles with the formation of molecular hydrogen. The molecules of neutral hydrogen then again fall on the day side, where they again dissociate, closing the cycle. Calculation of alternative models, in which hydrogen dissociation does not occur, requires the presence of fast winds on the planet, moving at a speed of about 60 kilometers per second - which seems unlikely, the authors explained.
The study is published in the Astrophysical Journal.