In the search for moons outside our solar system, the most sensitive hunt ever conducted came up empty — and that's actually a reason to celebrate. Astronomer David Kipping of Columbia University, best known for hosting the Cool Worlds YouTube channel, wanted to prove a point: the James Webb Space Telescope (JWST) has what it takes to spot an exomoon, a moon circling a planet in another star system. For years, many scientists feared the telescope had a built-in "noise floor" that would block it from ever finding such small objects. Kipping just showed that fear was wrong.
The catch is that JWST hasn't actually found any exomoons yet. Not a single one. The culprits, until now, seemed to be glitches in the telescope's instruments and wandering "red noise" from the star itself — slow, sneaky changes like a detector warming up, the telescope's aim shifting slightly, or sunspots drifting across the star's surface. Previous efforts, like watching the gas giant Kepler-167 e, watched just one passing of the planet across its stareb and got swamped by that noise, making anything smaller than Earth impossible to detect.
Kipping's fix is beautifully simple: average. Moons obey the laws of physics, so they appear in the same predictable spot every time a planet crosses its star. Instrument glitches and sunspots, on the other hand, show up differently on every pass. Combine data from many transits bugs, and the noise smooths away, leaving a clean signal.
To test this, Kipping dug into JWST's observations of LP 890-9 c, a rocky planet orbiting an ultracool red dwarf about 105 light-years away. With an 8.46-day orbit, the planet hugs its star closely, yet it sits in the habitable zone of that remarkably cold host. Kipping was able to pull data from 12 separate transits. One of those passes suffered from heavy red noise, but when combined with just one clean pass, the sensitivity shot up dramatically.
The result: with 95% confidence, there are no moons larger than 0.1 Earth radii hiding around LP 890-9 c — no Io, no Europa, no Enceladus. That's a null result by design. The tides from the star, which the planet orbits at less than a tenth of the distance between the sun and Mercury, would strip any moon away or crush it into rings within billions of years. Kipping never expected to find one here. He used this planet as a proof of concept.
And the proof is stunning: JWST can detect moons the size of our own Moon, provided astronomers commit to watching multiple transits. That's easier said than done, since telescope time is among the most precious things in astronomy. But for the first time, the path to finding an exomoon looks wide open. We just need a bit more time.