On June 5th, 2017 we learned about

Enormous, incandescent exoplanet glows hotter than some stars

Stars are often compared to fireballs, but a new exoplanet named KELT-9b has been found to make a much stronger claim for that title. The huge gas giant’s atmosphere glows at temperatures around 7,800º Fahrenheit. It zips around its star every day-and-a-half, trailing a tail of red-hot particulate behind it. The only catch to the fireball analogy is that there may not be any actual combustion taking place on KELT-9b. Everything is so hot, a lot of it’s gaseous atmosphere is just metal ions circulating around the planet.

Piping-hot planet

Unsurprisingly, this blazing existence isn’t really sustainable. The heat causes the planet to glow also causes the expansion of the gases in the atmosphere. That might be fine, except that the planet is also incredibly close to the local star, KELT-9, hence that very short year around a considerably-sized star. As a result, the planet’s atmosphere is blasted with enough energy to strip away around 11 million tons of material every second. If that wasn’t enough, over the course of the next 200 million years, the star is expected to expand, eventually reaching the point where it will graze the super-heated atmosphere of KELT-9b. At that point, the planet might be reduced to a small, rocky core that remains in orbit, or be disintegrated and absorbed by the star itself.

In the mean time, a silver, or rather, glowing crimson lining may be on the back of the planet. KELT-9b is tidally locked, meaning it has no day or night cycle. The side of the planet that permanently faces the star reaches the peak temperatures mentioned above, but even the backside remains hot to glow like an ember. Estimates put the “darker” side of the planet at temperatures still exceeding some cooler stars in the galaxy, thanks to the heat distributed by the swirling, metallic atmosphere.

Unusual target for observation

Obviously, this is not the “Earth-like” conditions NASA usually hunts for when looking for exoplanets. KELT-9b was actually discovered using the Kilodegree Extremely Little Telescopes (KELT), devices built using less specialized components to search among hotter stars that typically blind us to the presence of orbiting planets. However, the glowing atmospheric conditions and bulk twice that of Jupiter made it possible to spot KELT-9b as it passed in front of it’s host star. At around 18,000º Fahrenheit, KELT-9 is a hot, bright star which makes observations difficult, but more instruments will be looking at that part of the sky soon to see more details about this bizarrely intense planet.


My second grader asked: Does it have any moons?

Probably not? The first concern is that tidally-locked bodies have a really hard time holding onto their satellites, as things easily spin in or spin out of orbit if the planet isn’t spinning. In this particular case, there’s also the proximity to the star to consider, which might be close enough to scoop up any moons in the area. Finally, spotting a moon 650 light years away around a planet, even a glowing one, it’s easy to do, so we probably won’t see anything around KELT-9b any time soon.

Source: Kelt-9b: astronomers discover hottest known giant planet by Ian Sample, The Guardian

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