Exoplanet hotter than some stars

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Astronomers have identified an Jupiter-sized exoplanet with a surface that is apparently hotter than the surfaces of some stars.

With a day-side temperature of 4,600 Kelvin (more than 7,800 degrees Fahrenheit), planet KELT-9b is hotter than most stars, and only 1,200 Kelvin (about 2,000 degrees Fahrenheit) cooler than our own sun…. For instance, it’s a gas giant 2.8 times more massive than Jupiter but only half as dense, because the extreme radiation from its host star has caused its atmosphere to puff up like a balloon. And because it is tidally locked to its star—as the Moon is to Earth—the day side of the planet is perpetually bombarded by stellar radiation, and as a result is so hot that molecules such as water, carbon dioxide, and methane can’t form there. The properties of the night side are still mysterious—molecules may be able to form there, but probably only temporarily.

The most interesting aspect of this discovery is that it was done with small, inexpensive ground-based telescopes.



  • wayne

    Where is this KELT-9, star, located? (and how far away is it?) I didn’t catch it in the article.

    Might it not be more correct to say, “it’s hotter than the surface, of our own Sun?” (I thought the interior of our Sun, was ‘like, 20 million degrees?)

    (Goes without saying– this is all very cool. Worlds without end, to be sure!)

  • Wayne: Your point is taken. I have revised the wording of the post, as the temperatures were referring to the surfaces of stars.

  • wayne

    Mr. Z.
    Thank you.
    (-Wasn’t trying to be picky, the Sun’s “temperature” has confused me to no end in the past. If I’m recalling correctly, we don’t know the complete mechanism by which heat is transferred throughout a star.)

    I’d be highly interested in what this KELT-9b, is composed.

    And yes– very cool they used equipment that doesn’t cost a fortune.

  • Wayne: You are recalling right. Solar scientists and physicists do not yet understand the process whereby the heat in a star’s interior transfers outward to the surface. They also really do not understand in detail the nuclear processes going on there.

    Which, by the way, is why I remain skeptical of any predictions concerning the Sun’s solar cycle. Sunspot activity hints at the possibility of an upcoming grand minimum, but don’t bet on it. We do not understand the process yet.

  • wayne

    Excellent segue to Sun spots!

    I would tangentially shill for a Gresham College, Public Lecture.
    Part of a lengthy Series the Professor did in 2014.
    Good visuals & covers a wide range of Sun topics, although not deeply.

    (our friend, the sun)

    “The Sun, our Nearest Star”
    Prof. Carolin Crawford
    Gresham College Public Lecture

  • Max

    Our Sun ranges from a theoretical 50 million degrees in the center, to 11,000° on the surface.(photosphere) It cools off another 4000° 250 miles above the surface. The temperature goes back up to near 2 million° In the chromosphere but there is no upper limit, it’s been measured near 18,000,000°
    This violates the laws of thermodynamics, and the radiation is low. There should be a factor of three more neutrons (gamma radiation) as a byproduct of a large nuclear reaction. Enough radiation to make this world lifeless


    Although this probe launches next year, it will be another six years before we receive data on how our Sun works… I don’t think they will tell us the truth because too much money is spent on hot fusion.
    This Jupiter like planet must be skimming the surface of the sun that is larger than ours. 36 hours is incredibly fast. So it has 1/2 Jupiters mass. But 2.8 times larger to dim the star as much as it does…?
    Many compounds form anyway in hot temperatures, chronal mass ejections from our own Sun throw methane, ammonia and other gases that burn up in our atmosphere as the Aurora Borealis. Ionizing radiation makes other compounds like Ozone, nitrous oxide in earths ozone layer but does not penetrate very far. On Venus it does not pass the upper atmosphere. None of the suns heat reaches the surface of the planet.


    Even though Venus is nearly tidel locked, it’s atmosphere is not. It moves around the planet once every two days. (48 hours). There are a lot of assumptions in this article, many of which do not occur in our own solar system. I’ll try to keep an open mind to the possibilities anyway… I do enjoy science fiction.

  • LocalFluff

    The Parker Probe, as we should call Solar probe Plus now in memory of a heliophysicist, for once, who predicted the Solar wind, will give good data already November 1st 2018, only 3 months after launch, when it reaches its first perihelion 36 Solar radii from the Sun. One Solar radius is roughly ½% of the distance Earth-Sun so this is less than half the distance of Mercury. 30 times more intense Solar radiation than at Earth.

    Venus flyby’s means looong travel times for interplanetary probes going outwards. But this thing will fly by the Sun each time it passes by Venus. It’s a Solar clipper. It will edge closer and closer until 10 Solar radii perihelion in 2024 (400 times more intense radiation! if the corona doesn’t change this law of squares). And I guess they can extend this mission too.

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