ULTRAHOT JUPITERS ACT LIKE STARS
Their atmospheres are intense enough to rip water molecules apart
A pair of recent studies into ultrahot Jupiters have revealed that they are super-heated to the point of acting act like stars, with atmospheres so intensely hot they can tear water molecules apart, and vaporise iron and titanium.
Ultrahot Jupiters are gas giants that are tidally locked to their star, meaning that one side is constantly in daylight. As these worlds are also in a tight orbit, temperatures can reach 4,000°C , which is hotter than many stars.
The spectra of these worlds – which indicate what elements and compounds are in their atmospheres – has confused astronomers for many years. To help understand what’s going on in the atmospheres of these odd worlds, one group of researchers recently simulated the atmosphere of ultrahot Jupiter KELT-9b.
“The results of these simulations show that most of the molecules found there should be in atomic form, because the bonds that hold them together are broken by collisions between particles that occur at these extremely high temperatures,” says Kevin Heng from The University of Bern, who led the study.
This means that metals would be vaporised by the heat, making them detectable. This was indeed confirmed when astronomers made follow-up observations of KELT-9b and found titanium and iron in the atmosphere. Considering the planetary atmosphere to be more like that of a star’s than a planet’s led another group, headed by Vivien Parmentier from Aix Marseilles University, to uncover a different mystery regarding ultrahot Jupiters. Astronomers expected them to be rich in water, but instead they appear almost completely arid. This study found that the extreme heat of the starlit side would tear apart the water molecules in the atmosphere, creating oxygen and hydrogen. However, the dark sides of ultrahot Jupiters are thousands of degrees cooler and the disparity creates powerful winds that carry these elements into an atmosphere that’s cold enough for them to reform. As the dark side is constantly in shadow, this can’t be confirmed directly through observation, but it could explain why traces of water have been spotted along the terminator between day and night. “With these studies, we are bringing some of the century-old knowledge gained from studying the astrophysics of stars to the new field of investigating exoplanetary atmospheres,” says Parmentier.
Ultrahot Jupiters have one side that always faces their sun, which is one reason they heat up to such extremes