There are planets so near their stars that they’ve magma oceans 100 km deep and winds at 8000 km / h


200 light years away, the exoplanet K2-141b of the “super earth” orbits a star so precisely that its “year” is only 7 hours long. Not his day … his YEAR! K2-141b orbits just a million kilometers from the fiery surface of its star. The earth is 150 million km from our sun. Even Mercury, the planet closest to our sun, is never less than 47 million km away. When you stand on the surface of K2-141b you will see an orange star that fills fifty degrees of the sky and appears a hundred times wider than our sun in the sky of the earth. It would be a giant flaming sphere so bright that its light shines two-thirds of the way around the entire planet, unlike the two day / night halves of the earth. Of course, the surface you're standing on wouldn't be a large surface at all – it would be an ocean of liquid hot magma.

Artist's impression of a closely orbiting exoplanet around a star. c. ESO

Lava Planet

We have discovered a number of "lava planets" or "magma worlds" in the Milky Way. These planets are so close to their stars that their surface has literally merged into an eternal ocean of lava. The surface is also partially evaporated by the constant bombardment with solar radiation and thrown around the planet by supersonic winds, creating an atmosphere that is literally made up of evaporated rock. The planet, the oceans, the atmosphere – just rocks and minerals in different states of solids, liquids and gases. No water. No air. Certainly no life. Just a planet made of "living" rock.

Of all these observed lava worlds, K2-141b is ideal for studying. This world was discovered in 2018 and has one of the tightest and shortest orbital times of any known rocky exoplanet. It also has the best signal-to-noise ratios of any world and provides scientists with the best quality data. Lead author Giang Nguyen – PhD student at York University; With a team of researchers from York, McGill University and the Indian Institute of Science Education, the possible conditions of this world were modeled using computer simulations.

Supersonic atmosphere

In sunlight, the surface temperature of K2-141b is 3000 degrees Kelvin, which evaporates minerals and creates a thin atmosphere that sticks to the planet. The research team modeled three possible atmospheric compositions based on the presence of minerals and elements found in the rocky earth's crust – sodium (Na), silicon oxide (SiO), and silicon dioxide (SiO2). For each model, the predicted atmospheres were thinner than Earth's. The thickest variant produced by sodium created an atmosphere with a pressure of 13.9 kilopascals (kPa) (the earth's atmosphere at sea level is 103.325 kPa). The thinnest was SiO2 with only 240 Pa. In all of the predicted atmospheres, the wind speeds generated by the proximity to the star were surprisingly fast. A supersonic vortex. Wind speeds of 2.3 km / s prevailed in a sodium atmosphere. Per second! That is more than 8000 km / h.

These winds are drifting to the other side of the planet – that side in constant darkness. K2-141b is so close to its parent star and is tide locked. The same side of the planet is always facing its star while the other side is always facing the darkness of space. In contrast, the dark side of the planet is a cold -200 Kelvin. As minerals near the boundary between day and night, they cool down and rain or "snow" all the way to the planet's magma ocean, where they flow back into direct sunlight. This means that the atmosphere is mostly confined to the day side of the planet.

An ocean of magma

The entire cycle is similar to the water cycle on earth, in which sea water evaporates, rains on land and flows back into the ocean … only with magma-hot stones. Sodium, which is the most volatile of the possible atmospheres, is carried further into the night side of the planet, meaning that it can rain past the shores of the Magma Ocean onto the solid rock, which is itself confined to the day side of the planet as well . This sodium would then be transported on glaciers like solid surface plates that would eventually find their way back to the magma ocean. The research team was able to predict the maximum depth of the magma ocean based on the planet's gravity, heat and density. Since the gravity of K2-141b is twice that of Earth because it is five times as massive, the planet could create an ocean of magma with a depth of over 100 km. The deepest regions of the Earth's seas are only 11 km away. Models predict that in some scenarios the rate of mineral flow back to daylight may be too slow, resulting in more mass on one side of the planet than the other. The planet would be thrown out of whack, resulting in a "realignment of the planet's spin". In principle, K2-141b could be knocked off its axis by the constant bursting of its star.

Future super-scope observations

Currently, telescopes do not have the resolving power to see the exoplanet's atmosphere, but the next generation of rifle scopes like the James Webb Space Telescope will. There is another challenge. The atmosphere is on the wrong side of the planet. Since most of the atmosphere of 141b rains before reaching the dark side, there is a concern that we may not be able to see the atmosphere from our point of view. By the time the planet turns around during its year, it will have traveled behind the star. Given the extreme viewing angles created by the star's narrow orbit and the amount of light bleeding around the planet's curve, the research team decided that a telescope should be able to see up to 26 degrees beyond the planet's hemisphere see it appears or disappears behind its star. A telescope could then look into the region where the supersonic atmosphere is located and confirm not only the composition of the atmosphere but also the predicted wind speeds.

Artist's rendering of Earth's Hadean period is the earliest geological age when it was first established. During this time, the earth would also have shown magma oceans and intense volcanic activity. C. Wikimedia Tim Bertelink CC BY-SA 4.0

Lava earth

The view of other worlds helps us to understand not only the wider universe, but ultimately our own planet. Studying K2-141b offers an insight into our history. Planet earth was melted at least twice. Our first molten period was at the very beginning when our planet was fresh off the assembly line of the solar system that was warmed by the accumulation of all the things that made us. The second period followed the massive impact of a Mars-sized object that resulted in the formation of the moon and literally melted the entire earth. Whether Mars, Venus or K2-141b – all of these worlds give an insight into the past of our own planet and provide information about where in the future we may find a planet that is similar to ours in the present.

More to discover

K2-141b in NASA's Exoplanet Catalog

Supersonic winds, rocky rains 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 do we get there? – Universe Today Video

The color of habitable worlds – the universe today

James Webb works perfectly! On the ground. Next trick: From space – universe today

What is a super earth? – universe today

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