On the exoplanet KELT-9b the day is so hot that it breaks hydrogen molecules

Artist's concept of the exoplanet KELT-9b (Image NASA/JPL-Caltech)
Artist’s concept of the exoplanet KELT-9b (Image NASA/JPL-Caltech)

An article published in “The Astrophysical Journal Letters” reports a study of the exoplanet KELT-9b with evidence that the conditions are so extreme as to break hydrogen molecules. A team of researchers led by Megan Mansfield of the University of Chicago used NASA’s Spitzer space telescope to find evidence that KELT-9b is an extreme example even in the hot Jupiter planet class due to the conditions existing on its surface. Not accidentally, it’s the hottest known planet and on its dayside hydrogen molecules are broken and then recompose when the atoms move on its nightside.

About 670 light years from Earth, the exoplanet KELT-9b was discovered thanks to transits detected since 2014 by one of the two Kilodegree Extremely Little Telescopes (KELT). It orbits very close to its star, to the point that its year lasts only 36 hours, with the consequence that it’s tidally locked to it. An article published in the journal “Nature” in June 2017 reported a study of the planet KELT-9b that indicated that on its dayside the temperature on the surface can be higher than 4,600 Kelvin, higher than that of many dwarf stars.

The extreme characteristics of the exoplanet KELT-9b make it interesting for research, this new one conducted using NASA’s Spitzer space telescope. Repeated observations over many hours allowed to detect changes in the atmosphere of KELT-9b when, orbiting its star, it shows us different faces. Its nightside is much less warm than its dayside one, but the temperatures are still around 2,600 Kelvin.

The gases in the atmosphere of the exoplanet KELT-9b move from one side to the other and the researchers tried to create models that explain those flows. Computer simulations made it possible to test various hypotheses and the one that best matches the data includes hydrogen molecules broken by the heat of the dayside and then recomposed on the planet’s nightside. Megan Mansfield stated that the alternative would be winds at speeds of 60 kilometers per second (about 37 miles per second), unlikely even on such an extreme planet.

Peculiar conditions even for an ultra-hot Jupiter planet are useful also to better understand the atmospheres of exoplanets, in particular with the interactions between the radiation coming from the star and the heat flows on KELT-9b. In this specific case, it’s still unclear why the “hot spot” on this exoplanet’s dayside side isn’t in front of the star but is moving away from that position. The atmosphere’s ionization could create magnetic effects that generate this phenomenon and research continues to verify this theory.

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