One of the craziest exoplanets found in the Milky Way just got even more interesting. Astronomers have discovered the rare earth metal terbium swirling in clouds of vaporized metal in KELT-9b’s atmosphere; This extremely rare element has been found for the first time in a distant world. The team also confirmed previous detections by making new detections for vanadium, barium, strontium, nickel and other elements, suggesting that what was happening on KELT-9b was indeed very strange.

“We’ve developed a new method that allows us to get more detailed information. Using it, we discovered seven elements, including terbium, a rare substance that has never been found in the atmosphere of any exoplanet before,” says astrophysicist Nicolas Borsato of Lund. university in Sweden.

“It is very surprising to find terbium in the atmosphere of an exoplanet.”

KELT-9b is about 670 light-years away and is indeed one of the most extreme exoplanets. It’s called hot Jupiter, a gas giant that orbits so closely with its host star that it heats up to scorching temperatures.

Also, KELT-9b orbits one of the hottest stars, a blue supergiant, in just 1.48 days in an extremely narrow orbit.

This proximity greatly vaporizes the exoplanet: On the day side, KELT-9b heats up to temperatures in excess of 4,600 Kelvin (4,327 degrees Celsius, or 7,820 degrees Fahrenheit). This is the highest temperature we’ve ever seen on an exoplanet. Hotter than at least 80 percent of all famous stars.

Luckily, KELT-9b is orbiting between us and the star. This means that scientists are able to peer into its atmosphere.

As starlight passes through KELT-9b’s atmosphere, some wavelengths of light are absorbed and re-emitted by the gas atoms. The signal is small, but by aligning the orbits, astronomers can amplify the signal to see the brighter and darker parts of the star’s light spectrum as the planet transits compared to observations of the star itself.

It takes some analysis, but scientists can look at the signatures of these dark and light parts and determine which elements are causing the changes in light.

Thanks to these data, KELT-9b became the first exoplanet to detect evaporation of iron and titanium in its atmosphere in 2018. Then, a year later, the scientists announced that they had also found sodium, magnesium, chromium, and the rare earth metals scandium and yttrium.

Borsato and colleagues improved their analysis method to produce a more detailed breakdown of elements in the spectrum of KELT-9b and its host star. Their results confirmed previous detections of hydrogen, sodium, magnesium, calcium, chromium and iron and revealed several metals not seen in the exoplanet’s atmosphere.

The real surprise was terbium with atomic number 65. Here on Earth, the heavy element is extremely rare and is usually found in trace amounts with other elements. To date, we have not discovered any natural terbium predominant minerals; its amount in the earth’s crust is about 0.00012 percent.

It’s interesting to find it in another world, because heavy elements like terbium can only be created under the most extreme conditions, such as the explosion of a supernova or the collision of two neutron stars.

This is true for all elements heavier than iron, but finding terbium in the atmosphere of an exoplanet was completely unexpected, and it may tell us something about the history of KELT-9b and its star.

We know that both are relatively young when it comes to these things: about 300 million years old. (For context, the Sun is about 4.6 billion years old.) To contain heavy elements similar to those found in KELT-9b’s atmosphere, they would have to have formed from materials containing emissions from one of these powerful events.

Because such events occur at the end of a star’s life, the number of heavy elements in the universe increases over time. The older the star or exoplanet, the less heavy elements it will contain. In contrast, younger stars and exoplanets will have heavier elements and possibly more diversity.

“Learning more about the heavy elements helps us determine, among other things, the age of exoplanets and how they formed,” says Borsato.

The team’s work also improves methods used to analyze exoplanet atmospheres. Science is still fairly new, but it evolves in hours, not days; next generation telescopes will expand it exponentially. Not just for working on extremes like the KELT-9b. Scientists believe our first detection of life outside the solar system will be through detection of biological material in the atmosphere of another world.

“Detecting heavy elements in the atmospheres of superheated exoplanets is another step towards learning how planetary atmospheres work,” says Borsato. “The better we learn about these planets, the better our chances of finding Earth 2.0 in the future.”

The work has been accepted for publication in Astronomy & Astrophysics and is available on arXiv.