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200 light-years away, the “super-earth” exoplanet K2-141b orbits a star so closely that its “year” is only 7 hours long. It’s not his day … it is YEAR! K2-141b orbits just one million kilometers from its star’s fiery surface. The Earth is 150 million km from our Sun. Mercury, the closest planet to our Sun, is also never less than 47 million km. Standing on the surface of K2-141b you would be looking at an orange star filling fifty degrees of the sky and appearing a hundred times larger than our Sun appears in the earth’s sky. It would be a gigantic fiery globe so bright that its light shines two thirds of the way around the entire planet, unlike the two day / night halves of the Earth. Obviously, the surface you’re standing on would not be a surface at all – it would be an ocean of hot liquid magma.
Lava Planet
We have discovered a number of “lava planets” or “magma worlds” throughout the Milky Way. These planets are so close to their stars that their surface literally melts into a perpetual ocean of lava. The surface is also partially vaporized by the constant bombardment of solar radiation and is blown around the planet by super sonic winds creating an atmosphere that is literally just vaporized rock. The planet, the oceans, the atmosphere: just rock and minerals in different states of solid, liquid and gas. No water. Without air. Certainly no life. Just a “living” rock planet.
Of all these lava worlds observed, K2-141b is the ideal to study. Discovered in 2018, this world has one of the closest and shortest orbital periods of any known rocky exoplanet. It also has the best signal-to-noise ratios of all these worlds, providing the best data quality for scientists. Lead author Giang Nguyen – doctoral student at York University; with a team of researchers from York, McGill University and the Indian Institute of Science Education they modeled the possible conditions of this world using computer simulations.
Supersonic atmosphere
In sunlight, the surface temperature of K2-141b is 3000 degrees Kelvin which evaporates the minerals to create a thin atmosphere clinging to the planet. The research team modeled three possible atmospheric compositions based on the presence of minerals and elements common to the earth’s rock crust: sodium (Na), silicon oxide (SiO) and silicon dioxide (SiO).2). With each model, the predicted atmospheres were more subtle than those on Earth. The thicker variant, created by sodium, produced a pressure atmosphere of 13.9 kilopascals (kPa) (Earth’s atmosphere at sea level is 103.325 kPa). The thinnest was SiO2 at only 240 Pa. But in all expected atmospheres, the wind speeds created by the proximity to the star were surprisingly fast. A supersonic vortex. A sodium atmosphere exhibited wind speeds of 2.3 km / s. For SECOND! That’s more than 8000 km / h.
These winds drive towards the far side of the planet – this side in perpetual darkness. Being so close to its parent star, K2-141b is martially locked. The same side of the planet is always facing its star while the other side is always facing the darkness of outer space. In contrast, the dark side of the planet is a frigid -200 Kelvin. As the minerals approach the border between day and night, they cool down and rain or “snow” to the planet’s magma ocean where they ebb in direct sunlight. This means that the atmosphere is mostly confined to the day side of the planet.
An ocean of magma
The whole cycle is similar to the water cycle on Earth, where sea water evaporates, rains on land, and flows back into the ocean … only with hot magma rocks. Sodium, being the most volatile of possible atmospheres, is carried farther into the night side of the planet, meaning it can rain on solid rock beyond the shores of the magma ocean which is itself limited to the day side of the planet. This sodium would then be transported to the glacier as solid surface plates that eventually return to the magma ocean. The research team, using the planet’s gravity, heat and density, was able to predict the maximum depth of the magma ocean. With K2-141b’s gravity twice that of Earth, as it is five times more massive, the planet could produce an ocean of magma over 100 km deep. The deepest regions of the Earth’s aquatic oceans are only 11km. The models predict that, in some scenarios, the speed of mineral flow in daylight may be too slow resulting in more mass on one side of the planet than the other. The planet would become unbalanced resulting in a “reorientation of the planet’s rotation”. Basically, K2-141b could be pushed off its axis by the continued burst of its star.
Future Super-Scope Observations
At present, telescopes don’t have the resolving power to see the exoplanet’s atmosphere, but the next generation of telescopes, such as the James Webb Space Telescope, will. There is another challenge. The atmosphere is on the wrong side of the planet. Since most of 141b’s atmosphere rains before we reach the dark side, there is concern that we won’t be able to see the atmosphere from our vantage point. When the planet turns during its day-side year, it has traveled behind the star. But given the extreme viewing angles created by its star’s orbit so closely and the amount of light bleeding around the planet’s curve, the research team determined that a telescope should be able to see up to 26 degrees beyond. the hemisphere of the planet just as it appears or disappears behind its star. A telescope could then peer into the region where the supersonic atmosphere resides and confirm not only the composition of the atmosphere but also the predicted wind speeds.
Lava land
Looking to other worlds helps us understand not only the larger Universe, but ultimately our planet. Studying K2-141b provides a glimpse into our history. On at least two occasions, the planet Earth was melted. Our first period of merger was at the very beginning, when our planet had just rolled off the assembly line of the solar system heated by the accretion of all the things that produced us. The second period followed the massive impact of a Mars-sized object that led to the formation of the Moon and literally melted the entire Earth. So whether it is Mars, Venus or K2-141b, all of these worlds are a glimpse into our planet’s past and provide insight into where, in the future, we might find a planet that looks like ours in the present.
More to explore
K2-141b in NASA’s exoplanet catalog
Supersonic winds, rock showers predicted on the lava planet – McGill
Modeling the atmosphere of the lava planet K2-141b: implications for low and high resolution spectroscopy – Nguyen et al 2020
100 million exoplanets by 2050? How will we get there? – Universe Today Video
The color of habitable worlds – Universe Today
James Webb works perfectly! On the ground. Next trick: do it from space – Universe Today
What is a Super Earth? – Universe Today
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