How Many Planets Orbit Our Nearest Neighboring Star?

Some of the most promising places to look for extraterrestrials have remained, so far, mostly hidden from astronomers. Now a game-changing instrument called NIRPS (Near-Infrared Planet Searcher) is leading the search for the most tantalizing targets in the cosmos: potentially Earth-like worlds around nearby red dwarf stars.

Red dwarfs, or M dwarfs, are the most tempting places to seek alien Earths because they’re the most abundant and enduring stars. They make up the majority of the stars in the Milky Way and shine with a slow thermonuclear simmer that should allow them to live exponentially longer than most—even, say, for 14 trillion years, or 1,000 times the current age of the universe.

But M dwarfs are also the smallest, dimmest stars, so they and their planets can be difficult to detect and inspect. Enter NIRPS, an instrument custom-built to tease out subtle signs of otherwise hidden worlds by making unmatched high-precision measurements of M dwarfs, which emit most of their light in infrared and near-infrared wavelengths.

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“I think we are in the golden age of M dwarfs, where they offer a huge amount of possibility—they are the best place to detect small Earth-sized planets,” says Natalie Hinkel, a planetary astrophysicist at Louisiana State University, who is not a member of the NIRPS team.

The M Dwarf Frontier

NIRPS can find planets via the radial velocity (RV) method, which looks for the tiny gravitational tug they exert on their stars. This tug ever-so-slightly changes the star’s velocity, which in turn almost indiscernibly changes the color of its light. When an orbiting planet tugs its star closer to Earth, the star’s light shifts slightly to the blue end of the spectrum in our telescopes; when the planet tugs its star away, the starlight shifts slightly to the red end. The cyclic blue-to-red stellar wobble that is the RV signature of a small world orbiting an M dwarf corresponds to a velocity shift of less than a meter per second. M dwarfs are especially well suited for RV planet surveys because their low masses can result in larger, more obvious tugs from any accompanying tiny worlds.

René Doyon, a professor at the University of Montreal and co-principal…