It's been just eight months since scientists announced their discovery of a small dim star called TRAPPIST-1 and the seven rocky planets that orbit it—but the news keeps coming. Scientists already think the system may be capable of holding liquid water. Now a new paper published today in the journal Nature Astronomy argues that two of the star's planets have sported oceans of liquid magma and that four of them have been heated by the quirky properties of their star.
TRAPPIST-1 doesn't look much like our sun. It's colder, smaller, fainter, and redder—and the planets that orbit it are stuck with one side permanently turned toward it, the same way the Moon circles Earth. "We choose the TRAPPIST-1 system for our study, because it is truly a remarkable family of planets," lead author Kristina Kislyakova, an astrophysicist at the University of Vienna in Austria, wrote to Newsweek in an email. "This star is also a nice example of an M dwarf we were interested in: it has a very low mass, a strong magnetic field, and rotates very fast."
If that strong magnetic field and fast rotation line up in just the right way, Kislyakova and her co-authors thought, they could cause a phenomenon called induction heating. That's when an electromagnetic field creates heating currents within the surface of a metal object. (That means this whole theory wouldn't work for planets orbiting a star like Proxima Centauri, our sun's nearest neighbor, says David Rothery, a planetary scientist at the Open University in the United Kingdom not affiliated with the study, but he also worries that even for TRAPPIST-1, the magnetic field and rotation may not align quite right.)
"Some low-mass stars have very strong magnetic fields, and we were joking that these fields might melt a fork or a spoon, if one moves it from one place to another on a planet orbiting such a star," Kislyakova wrote. "And then we realized that the planet itself is actually also embedded in this strong magnetic field and is a conducting body"—basically, that the there was a giant fork poised to be melted.
And so they looked at the seven planets orbiting TRAPPIST-1 to see whether any of them could be heated by the star's strong magnetism. That required some guesswork, since we don't yet have precise sizes or ingredient lists for any of the Trappist planets. But the calculations Kislyakova and her co-authors made suggest that the four planets closest to TRAPPIST-1 have all experienced this type of heating, and that it likely has made them a little more volcanic.
And in two of them, called TRAPPIST-1c and TRAPPIST-1d, the second and third planets away from the star, there might be enough induction heating to sustain an ocean of liquid magma tucked away beneath the surface. If that turns out to be true, these two planets would be similar to Jupiter's moon Io, which is covered in erupting volcanoes.
It's not clear yet what impact magma and its accompanying volcanoes would have on the odds of finding life. Giant eruptions can wipe out huge proportions of organisms, but smaller eruptions can help sustain an atmosphere. "The geology of many planets of M dwarfs is likely to be fascinating," Rothery says.
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