Using computer simulations, an international team of astronomers has studied the weather conditions on K2-141b, an Earth-size exoplanet with supersonic winds that rage over 5,000 km/hr (3,100 mph), the evaporation and precipitation of rocks, and a magma ocean about 100 km (62 miles) deep.
This artist’s impression shows the lava exoplanet CoRoT-7b, which is so close to its Sun-like host star that it must experience extreme conditions. Image credit: ESO / L. Calcada.
Lava planets are a class of rocky exoplanets that orbit so close to their star that parts of their surface are molten.
Indeed, dayside temperatures on these planets can be hot enough to maintain a rock vapor atmosphere.
Theoretical studies of lava planets and their relatively volatile sodium atmospheres have been published for CoRoT-7b, Kepler-10b, 55 Cnc e, KIC 12556548, and HD 219134b.
“Our study is the first to make predictions about weather conditions on K2-141b that can be detected from hundreds of light-years away with next-generation telescopes such as the future James Webb Space Telescope,” said lead author Giang Nguyen, a PhD student in the Centre for Research in Earth and Space Sciences at York University.
Nguyen and colleagues discovered that about two-thirds of K2-141b faces perpetual daylight, rather than the illuminated hemisphere we are used to on Earth.
Its night side experiences frigid temperatures of below minus 200 degrees Celsius (minus 328 degrees Fahrenheit).
The day side, at an estimated 3,000 degrees Celsius (5,432 degrees Fahrenheit), is hot enough to not only melt rocks but vaporize them as well, ultimately creating a thin atmosphere in some areas.
“Our finding likely means that the atmosphere extends a little beyond the shore of the magma ocean, making it easier to spot with space telescopes,” said Professor Nicolas Cowan, an astronomer in the Department of Earth & Planetary Sciences at McGill University.
Just like the water cycle on Earth, where water evaporates, rises into the atmosphere, condenses, and falls back as rain, so too does the sodium, silicon monoxide, and silicon dioxide on K2-141b.
On Earth, rain flows back into the oceans, where it will once more evaporate and the water cycle is repeated.
On K2-141b, the mineral vapor formed by evaporated rock is swept to the frigid night side by supersonic winds and rocks rain back down into a magma ocean.
The resulting currents flow back to the hot day side of the exoplanet, where rock evaporates once more.
Still, the cycle on K2-141b is not as stable as the one on Earth.
The return flow of the magma ocean to the day side is slow, and as a result they predict that the mineral composition will change over time — eventually changing the very surface and atmosphere of K2-141b.
“All rocky planets, including Earth, started off as molten worlds but then rapidly cooled and solidified,” Professor Cowan said.
“Lava planets give us a rare glimpse at this stage of planetary evolution.”
A paper on the findings was published in the Monthly Notices of the Royal Astronomical Society.
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T. Giang Nguyen et al. 2020. Modelling the atmosphere of lava planet K2-141b: implications for low- and high-resolution spectroscopy. MNRAS 499 (4): 4605-4612; doi: 10.1093/mnras/staa2487
