That’s the portrait painted in a new study by scientists from McGill University, York University and the Indian Institute of Science Education and Research in Kolkata published on Tuesday in the Monthly Notices of the Royal Astronomical Society.
The researchers described conditions on this planet, called K2-141b, which is located about 210 light-years from Earth. It orbits extremely closely around its star, which is just slightly smaller than our sun.
This “lava” planet completes a revolution in about six or seven hours, just about grazing the star’s surface as it hurtles through space.
By contrast, Mercury, the closest planet to the sun in our solar system, takes 87 days to orbit the sun.
“Almost half of the planet is molten magma,” said lead study author Tue Giang Nguyen, a doctoral student at York University in Toronto. “The atmosphere created by vaporized rocks spreads around the planet.”
That vaporized silicon dioxide, or quartz, forms clouds and rains or snows down onto the molten surface below, he said.
A weirdo planet
To discover an exoplanet — a planet that orbits around a star other than the Sun — astronomers measure the difference in the light a star emits when a planet is behind it in its orbit versus in front of it, Nguyen explained. When observed through a telescope on Earth, the star appears dimmer when the planet is in front of it, slightly obscuring the view from Earth.
Scientists have discovered thousands of worlds beyond our solar system using this method. Few of them, though, have such molten surfaces that drive such dramatic swings in a planet’s weather and structure. In the literature available, Nguyen saw that astronomers have only observed about a handful of lava planets.
Exoplanet K2-141b has winds that clock in at about 3,100 miles per hour (5,000 kilometers per hour), and its magma ocean is estimated to have a depth of about 86 miles (140 kilometers), according to Nguyen’s calculations.
The extraordinary winds dominate one side of the planet but are totally absent on the other.
The bright side of K2-141b is scorching, with temperatures likely around 5,400 degrees Fahrenheit, or 3,000 degrees Celsius. That hot side has an atmosphere made of silicon dioxide, more commonly known as quartz.
Because K2-141b orbits so closely in the brilliant glare of its star, about two-thirds of the world is illuminated at any given time. One-third is dark, making for a frigid planet with temperatures of minus 392 degrees Fahrenheit, or minus 200 degrees Celsius.
That two-third light/one-third darkness split is unusual compared to planets in our solar system, such as Earth and Jupiter, where half of the planet would be lit by the sun at any given time.
“It’s a planet that doesn’t make much sense at all. There’s nothing like it in our solar system,” said study coauthor Nicolas Cowan, an associate professor in the departments of physics and Earth and planetary sciences at McGill University in Montreal.
Lava planets are quite rare, Cowan noted — just one in 1,000 stars would be able to host one. But given the enormity of the cosmos, there could be billions of lava worlds out there.
Studying such an exotic planet could pay dividends, helping scientists understand a version of the conditions that existed on Earth during its formation, when it too was covered in molten lava billions of years ago. Looking closely at the lava planet could yield answers into how it — and Earth — came to be, Cowan said.
“It’s a weird, naked, rocky core of what used to be a bigger planet,” he said.
Search for another Earth
“Lava planets have certainly caught people’s imaginations, and they are a rare, but very real class of planets,” said Jonathan Fortney, a professor of astronomy and astrophysics at the University of California, Santa Cruz, in an email. “Unlike a planet like Earth, the material that makes up this planet’s atmosphere is literally the same materials that make up the crust.”
Fortney compared K2-141b, and similar lava planets, to Pluto, which is rich in nitrogen in the form of ice in its crust and gas in its atmosphere.
“Planets like this open up the prospect of using the atmosphere (which is always easier to study) to learn something about the composition of the crust, which is much more difficult to study,” he said via email.
Nguyen and Cowan both said they hope to continue studying the lava planet, which will soon be observable with the next-generation devices of NASA’s James Webb Space Telescope, scheduled to launch next year.
The new space telescope will enable them to take high-resolution spectrographs of the planet and more closely understand the composition of its interior, ocean and atmosphere.
“This is an incremental step in trying to find Earth 2.0. That’s an endgame for space exploration,” Nguyen said.