Episode for August 18th, 2023 Download

In this episode, we are going to take a look at an extreme planet.

Kelt-9b is a gas giant planet that orbits a star 670 light-years from Earth. It is so close to its star that its dayside temperature is 7,800 degrees Fahrenheit (4,300 degrees Celsius), hotter than some stars. This heat is so intense that it rips apart the molecules in the planet’s atmosphere, including hydrogen gas.

But its star, called KELT-9, is even hotter – a blue A-type star that is likely unraveling the planet through evaporation. The KELT-9 is only 300 million years old, which is young for a star. It is more than twice as large, and nearly twice as hot, as our sun. Given that the planet’s atmosphere is constantly blasted with high levels of ultraviolet radiation, the planet may even be shedding a tail of evaporated planetary material like a comet.

The discovery of Kelt-9b was announced in 2017 by a team of astronomers using the Kilodegree Extremely Little Telescope (KELT) system. The KELT system is a network of two robotic telescopes that are used to search for exoplanets.

Kelt-9b is a very massive planet, with a mass that is about three times that of Jupiter. The heat is caused by the proximity of the planet to its star. Kelt-9b orbits its star in just 36 hours, which means that it is constantly bathed in the star’s heat. The planet is also unusual in that it orbits perpendicular to the spin axis of the star. That would be analogous to the planet orbiting perpendicular to the plane of our solar system.

The extreme heat of Kelt-9b has a profound effect on its atmosphere. The heat is so intense that it rips apart the molecules in the atmosphere, including hydrogen gas. This process is called photodissociation. The broken-up atoms then flow to the nightside of the planet, where it is cooler. On the nightside, the atoms can recombine to form molecules again.

With each orbit, KELT-9 b twice experiences the full range of stellar temperatures, producing what amounts to a peculiar seasonal sequence. The planet experiences “summer” when it swings over each hot pole and “winter” when it passes over the star’s cooler midsection. So KELT-9 b experiences two summers and two winters every orbit, with each season about nine hours.

This process is happening constantly on Kelt-9b, which means that the planet’s atmosphere is constantly being recycled. This makes it very difficult for any life to exist on the planet.

The study of Kelt-9b and other hot Jupiters is helping astronomers to better understand the formation and evolution of exoplanets. It is also helping them to learn more about the limits of habitability in the universe.

In addition to being the hottest exoplanet known, Kelt-9b is also one of the brightest. This makes it a valuable target for further study. Astronomers are using telescopes like the James Webb Space Telescope to learn more about the atmosphere of Kelt-9b.

The study of Kelt-9b is just one example of the exciting discoveries that are being made in the field of exoplanet research. As astronomers continue to study these distant worlds, they are learning more about the diversity of planets that exist beyond our solar system. This knowledge is helping us to better understand our own place in the universe.