In the search for planets outside the solar system, astronomers have had many surprises: worlds that are dwindling at full speed, spinning upside down or looking like they are made of diamonds. The far away Dated-9 b, a large gaseous exoplanet 650 light years from Earth, has its own eccentricity. Discovered in 2016, it is the hottest known up to now. It exceeds 4,700º C on its daytime face, a temperature similar to that of our Sun and hotter than 80% of all the stars in the universe. Qualifying it as torrid is not enough.
Kelt-9 b orbits a star that is twice as hot as the Sun, at a distance ten times closer than that separating Mercury from our star. At 1.8 times the size of Jupiter and 2.9 times its mass, it is considered a ‘hot Jupiter’. Its full orbit lasts one and a half Earth days and it sports a gigantic, glowing tail of gas like a comet.
To learn more about Kelt-9 b, researchers at the University of California have used data from the Hubble Space Telescope to obtain the eclipse spectrum of the planet as it passes in front of its star. Later, as explained in
‘The Conversation’, They used software to extract the presence of molecules and found that there were many metals (made of molecules). The finding, released in
The Astrophysical Journal Letters, surprised scientists since it was previously thought that these molecules would not be present at such extreme temperatures, but would break down into smaller compounds.
Subject to the strong gravitational pull of its host star, Kelt-9 b is “tidally locked,” meaning that the same face of the planet is permanently facing the star. This results in a strong temperature difference between the day and night sides of the planet. As the eclipse observations probe the warmer day side, the observed molecules could be swept up by dynamic processes from cooler regions, such as the night side or from deep within the planet’s interior. “These observations suggest that the atmospheres of these extreme worlds are governed by complex processes that are not well understood,” they note.
In addition, Kelt-9 b has an inclined orbit of about 80 degrees, suggesting a violent past, with possible collisions, which is in fact also observed on many other planets of this class. “Most likely this planet was formed far from its parent star and that the collisions occurred while it was migrating inward, toward the star,” they say. This supports the theory that large planets tend to form far away from their host star in proto-stellar disks and capture gaseous and solid materials as they migrate toward their star.
Today’s observatories, like the Hubble Space Telescope, were not designed to study exoplanet atmospheres. So researchers are confident that the next generation of space telescopes, such as the James Webb and the Ariel mission, will have much better capabilities and instruments designed for this task. The authors believe that these telescopes will answer many of the fundamental questions posed not only by large extremely hot Jupiter-like planets, but also by smaller worlds. Then we can know how they formed and evolved.
Unfortunately, Kelt-9 b doesn’t have a great future ahead of it. A study published in 2018 reveals that the atmosphere of this world is dragged by the gravitational force of its star. Practically, the planet is being absorbed.