KELT-9b: This Planet's Atmosphere Is so Hot It Can Vaporize Heavy Metals

The sun sets in this artist’s illustration of planet KELT-9b. Its nearby warm blue star is about 70 times the apparent size of the sun in the Earth’s sky. Under this scorching sun, the planet’s atmosphere is warm enough to shine in reddish-orange tones and vaporize heavy metals such as iron and titanium. Denis Bajram

Last year, astronomers made an intriguing discovery: a scorching planet, hotter than any other known to man, where dayside temperatures might exceed 4,000 Kelvin (6,740 degrees Fahrenheit). That would make it hotter than many stars.

Now, further intriguing details of this unusual exoplanet, dubbed KELT-9b, have emerged. According to a study published in the journal Nature, the planet's atmosphere contains heavy metals, such as iron and titanium, which take the form of a vaporized gas because of the extreme heat.

Iron is the most abundant transition metal—those in the center of the periodic table. However, it has never been directly detected in the atmosphere of an exoplanet because it is highly refractory, meaning it has a high melting point and, therefore, requires very high temperatures to be turned into a gas.

KELT-9b, which is located around 650 light years away, belongs to a class of planets known as "ultrahot Jupiters"—Jupiter-size exoplanets that orbit extremely close to their host stars.

KELT-9b, for example, is 30 times closer to its star, KELT-9, than the Earth is to the sun, completing an entire orbit in just 36 hours. As a result, like other ultrahot Jupiters, its atmosphere becomes so hot that the chemistry within resembles that of a star more than a planet.

Currently, we do not know what KELT-9's atmosphere looks like and how it can evolve under such conditions. To understand more, a team of researchers from the University of Bern created computer simulations of the planet's atmosphere.

These simulations predicted that it should be possible to detect metals like iron and titanium as single atoms because the bonds that usually join them together with other atoms will be broken by the high-energy collisions taking place between particles at extremely high temperatures. That's according to Kevin Heng, an author of the study from the University of Bern.

Armed with this knowledge, astronomers from the University of Geneva (UNIGE) observed the planet during transit. When this happens, light from the star is filtered through the planet's atmosphere, enabling scientists to learn about its composition using an instrument known as a spectrograph.

These devices spread white light into its component colors, a spectrum in which the chemical "fingerprints" of different substances can be identified. As the researchers dug into the data, they found evidence of both titanium and iron existing both as single atoms and a gas in the atmosphere.

"This is the first time they have been so definitively and robustly detected in any exoplanet," Heng told Newsweek.

The results prove the effectiveness of new techniques for studying ultrahot Jupiters, a class of planets that were only identified about a decade ago. They are still perplexing scientists with their curious properties and unusual atmospheres.

Most planets in KELT-9b's situation, for example, would have completely evaporated atmospheres. Some researchers think that its large mass may be sufficient to prevent total evaporation from happening, however.

"This planet is a unique laboratory to analyze how atmospheres can evolve under intense stellar radiation," David Ehrenreich, principal investigator with the UNIGE's team, said in a statement.

The methods used could also have implications for scientists hunting for life outside the Earth, according to Heng.

"The technique itself is exciting, because it uses a so-called spectrum at high resolution to detect these metals," he said. "Atoms and molecules have distinct spectral fingerprints. Given enough of these signatures, we can be sure of detecting a specific atom or molecule, and this is precisely what our study reports."

"You can imagine that this technique can be used to detect any atom or molecule of interest, including those that hint at biology (i.e., biosignatures). It is not inconceivable that this technique can be used to detect biosignatures in yet-to-be-discovered exoplanets in the foreseeable future."