According to Gizmodo, astronomers have proposed a new method for finding exomoons and, in the process, may have identified the first real candidate. The potential moon orbits HD 206893 B, a Jupiter-like exoplanet about 133 light-years from Earth. The team used high-precision astrometry—mapping stellar positions—to detect a wobble in the planet’s motion, suggesting a companion. The candidate moon is estimated to be about 0.4 Jupiter masses, which is over seven times the mass of Neptune, while the host planet is a whopping 28 Jupiter masses. This comes just months after NASA officially confirmed the discovery of the 6,000th exoplanet, highlighting the stark contrast with zero confirmed exomoons. The research is detailed in a forthcoming paper in Astronomy & Astrophysics and is currently available as a preprint.
Why exomoons are so hard to find
Here’s the thing: finding 6,000 planets but zero confirmed moons seems weird, right? Our own solar system is packed with them. But the challenges are massive. Basically, if a planet is a speck of dust on a cosmic scale, a moon is a speck on that speck. The main methods for finding exoplanets, like watching for a star’s light to dim as a planet passes in front (the transit method), struggle with something so small and faint. There’s also no strict definition of what an exomoon even is—could it be a binary planet? And like with exoplanets, every candidate has to survive brutal scrutiny to rule out false signals from things like asteroids or instrument glitches. NASA itself has about 8,000 exoplanet candidates still waiting for confirmation, so the bar is high.
How the new astrometry method works
So what’s different this time? The team didn’t rely on transits or radial velocity wobbles in the star. Instead, they used astrometry to directly measure the spatial wobble of the planet itself. Think of it like this: if you watch a planet’s precise path through space and it jiggles slightly, that jiggle could be caused by the gravitational tug of an unseen moon orbiting it. They tested this using the super-precise GRAVITY instrument on the Very Large Telescope in Chile, focusing on the exoplanet HD 206893 B. By carefully tracking a secondary signal near the planet, they could not only suggest a moon’s presence but also estimate its size and orbit. It’s a clever repurposing of an old technique with new, high-precision tools.
Is this the real deal?
The researchers are excited but very cautious. They “emphasize the tentative nature of this candidate,” which needs more data from GRAVITY for confirmation. And let’s be real—it’s a wild candidate. A moon that’s seven times Neptune’s mass orbiting a planet that’s 28 times Jupiter’s mass? We’re talking about a system of giants that blows our solar system’s scale out of the water. If confirmed, it would challenge our ideas about how moons form and what’s possible. But even if this specific signal turns out to be a dud—and it might—the real win here is proving the method. The paper argues that this astrometric approach, especially with next-gen instruments, could “usher in a new era of comparative exolunar science.” It’s about adding another tool to the toolbox.
What it means for the future
Look, the hunt for exomoons isn’t just about checking a box. Moons in our system, like Europa or Enceladus, are prime targets in the search for life. Finding them around other stars opens up a whole new category of potentially habitable worlds. This new method is a step toward that. It’s a perfect example of multi-messenger astronomy: using multiple, complementary techniques to study one elusive signal. As the researchers note, this is meant to work alongside existing methods, not replace them. So while we wait for the community to pick apart this particular candidate, the groundwork is being laid. After 6,000 exoplanets, astronomers are finally inching toward that first, historic exomoon confirmation. And they might already be looking right at it.
