A distant world is being stretched by the powerful gravity of its neighbouring planets and star to extremes never seen before in a rocky planet. The stretching is so intense that this strange world鈥檚 surface is probably entirely molten and so hot that it glows.
at the University of California, Riverside, and his colleagues spotted this unusual planet in a system already known to have one larger world, a giant planet circling the star once every 55 days or so. The star, called HD 104067, is about 66 light years from Earth.
The researchers found a second planet, a Uranus-mass world circling the star every 14 days or so, using a technique called the radial velocity method, in which the gravitational pull of a planet on its star produces characteristic wiggles in the star鈥檚 light. Then, they spotted a possible third planet, this one only about 30 per cent larger than Earth, by looking for dips in the star鈥檚 light as the planet passed between it and our telescopes. These regular dips showed that the third planet, called TOI-6713.01, takes only about 2.2 Earth days to circle the star.
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鈥淭hat they found two new planets in an exoplanet system using two different techniques is awesome in itself,鈥� says at the University of Bordeaux in France, who was not involved in this work. But the really unusual details came out when the researchers ran simulations of the orbital dynamics of the whole system.
The two larger planets seem to have relatively eccentric orbits, following oval-shaped trajectories that whip in close to the star and then drift to the outer reaches of the stellar system. The gravitational pull of these worlds drags the smaller rocky planet into an eccentric orbit too, fighting with the pull of the star itself.
This combination of the gravity from the outer planets and the star creates what Kane dubbed a 鈥減erfect tidal storm鈥�, pulling on the inner world and stretching it like a lump of clay. 鈥淭ides are wimpy for planets on circular orbits,鈥� says Raymond. 鈥淏ut eccentric orbits cause flexing in a planet and drive volcanism by literally changing the planet鈥檚 shape every orbit.鈥�
This flexing of the planet鈥檚 innards as it changes shape produces extraordinary amounts of heat. 鈥淚t is injecting an incredible amount of energy into the planet,鈥� says Kane. 鈥淭he temperature of this planet is hotter than some stars, far above what you might need to get a molten surface.鈥� The research calculated that TOI-6713.01鈥檚 surface temperature could be up to about 2300掳C (4200掳F).
That is about twice as hot as the temperature at which cast iron melts, so hot that the planet probably glows. Depending on its geology, it could have constant volcanism well beyond the most volcanic object in our solar system 鈥� Jupiter鈥檚 moon Io 鈥� leaving a stream of gas in its wake.
If follow-up observations can determine the planet鈥檚 mass, we should be able to learn much more about its geology, shape and surface conditions. 鈥淓ach one of these diverse systems is important information on how you form planetary systems in general, because whatever picture we get of how that works, it has to match all of these,鈥� says at California State University, part of the research team. The strange orbits in this particular planetary system hint that it may have had a chaotic past.
arXiv
