Illustration of a volcanic exoplanet. Credits: Nasa, ESA, Csa, Dani Player
The astrophysicist Stephen Kane from UC Riverside had to double-check his calculations several times because he couldn’t understand how the planet he was studying could be so extreme. Similar to Io, the most volcanically active body in the Solar System, this planet also appears to be covered in so many active volcanoes that, seen from afar, it appears to be incandescent. The article describing the unusual discovery was published on The Astronomical Journal.
Launched in 2018, the Transiting Exoplanet Survey Satellite (Nasa’s Tess), searches for exoplanets orbiting the brightest stars in the sky. Kane was studying a star system called HD 104067, about 66 light-years away from the Sun, already known to host a giant planet. In that system, Tess had just found evidence of a new rocky planet, and while collecting data on that planet, she unexpectedly found another one, bringing the total number of known planets in the system to three.
The new planet discovered by Tess is a rocky planet like Earth, but 30% larger. However, unlike Earth, it has more in common with Io, Jupiter’s innermost rocky moon in the Solar System. The surface temperature of the new planet, Toi-6713.01, is 2,600 degrees Kelvin, hotter than that of some stars. “At optical wavelengths you could see a hot, hot planet with a surface of molten lava,” explains Kane.
Gravitational forces are responsible for volcanic activity on Io and this planet. Even though Io is very close to Jupiter, the other moons force it into an eccentric orbit around the planet, which in turn exerts a very strong gravitational pull. «If there were no other moons, Io would have a circular orbit around the planet and its surface would be calm. Instead, Jupiter’s gravity squeezes it so much that it continually erupts volcanoes,” Kane reports.
Likewise, in the system of HD 104067 there are two planets farther from the star than this new planet. These outer planets force the rocky inner planet into an eccentric orbit around the star, which crushes it as it orbits and rotates. This is an effect called tidal energy or tidal energy.
In the future, Kane and his colleagues would like to measure the mass of the hot planet and know its density, to assess how much material is available to be ejected from volcanoes. Kane says tidal effects on planets have historically not received much attention in exoplanet research, and that perhaps with this discovery that will change.
“What we found teaches us a lot about the extremes of the amount of energy that can be released into a terrestrial planet and its consequences,” concludes Kane. “We know that stars contribute to a planet’s heat, but most of the energy is due to tides and this cannot be ignored.”
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