A Rocky Planet Around a Red Dwarf express
The tiny star LHS 3844 is trembling. The invisible culprit is a rocky planet that whips around it every 11 hours. The planet pulls on the star, and the star responds with a barely perceptible wobble. Detecting that wobble is like noticing a 100-kilogram weightlifter step forward when a fly lands on his palm.
To sense such a tremor, astronomers used the new CRIRES+ instrument on the Very Large Telescope in Chile. It observes in infrared light — the invisible heat radiation in which cool red stars like LHS 3844 shine brightest. The instrument tracks how lines in the star's spectrum shift back and forth, just as an ambulance siren changes pitch as it speeds past. From these shifts, they calculated that the planet weighs as much as 2.37 Earths and is only 29% larger in size. That means it's dense and rocky inside, like Earth, not a gas ball.
But there's a mystery: the star wobbles slightly more than a single planet should cause. Perhaps a second rocky world, completing an orbit every 6.88 days, is hiding nearby. For now it's just a hint, but if confirmed, the system becomes even more intriguing.
The real value of this discovery lies elsewhere. LHS 3844 b is the best known target for the James Webb Space Telescope. With no thick atmosphere, the telescope could directly observe its surface — what kind of rock it's made of. That would be the first time we see minerals on another planet. So a star's wobble turns into a map of a foreign world.
A year on LHS 3844 b lasts 11 hours and 6 minutes — shorter than a full workday with lunch break on Earth.
In Stanislaw Lem's novel Solaris, a planet-ocean also torments researchers — though there, it's the ocean studying humans, while here we may finally study a rocky surface.