If you examine the giant planets in our solar system, you’ll immediately notice that they all have moons—a Very Of moons. While Earth only has one, Jupiter has about 100 that we know of (and possibly hundreds more, depending on what you define as “moons”). Saturn has about 275!
Many of these moons are huge; Saturn’s titan and Jupiter’s Ganymede Both are the size of Mercury, and if they orbited the Sun themselves, we would be tempted to call them planets in their own right.
As if the moons weren’t enough, our quartet of more powerful planets (including Uranus and Neptune) also ring in. Of course, Saturn is the most obvious and iconic, but others also have rings, although they are fainter and harder to see.
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So it appears easier for giant planets to form moons and rings – at least around the Sun. This is probably true of the countless giant worlds we have discovered orbiting other stars; Many of these exoplanets should also have exomoons and exorings.
But could we find them?
The answer, which is very common in astronomy, is Perhaps.
Astronomers have already found several exomoon candidates. We can’t see them directly – they’re too faint and too close to their parent planets to resolve – but their presence can be inferred.
One of the most notable exomoon candidates, Kepler-1625b I, was first identified in 2017. A year ago, astronomers discovered its exoplanet via the transit method: We look at the edge of the planet’s orbit, so once per orbit, we can see the planet pass right in front of its star – a transit – creating a miniature eclipse. These transits usually appear as U- or V-shaped decline in a star’s brightness when plotted over time. Such a plot is called light curve.
However, there were some oddities with the exoplanet Kepler-1625b-There were strange bumps in the light curve associated with this that were difficult to explain. Astronomers theorized that this could be caused by an orbiting exomoon that sometimes follows the planet during its mutual transit and sometimes changes the shape of the light curve. If it is real, this exomoon would be quite large; Its apparent bulge in the light curve would be consistent with Neptune’s size. (The exoplanet itself is a so-called super-Jupiter, a giant world that may have a mass equivalent to a dozen Jupiters.) This claimed exomoon has proven controversial, however, with papers arguing for or against its existence. At the moment, it is still unconfirmedly a candidate.
Another exomoon-hunting method relies on transit time variation. As the exomoon orbits its host, its gravity rotates the planets around their common center of gravity, called the barycenter. This subtly alters the timing of planet transits, altering their estimated onset or duration by small amounts. Some configurations – such as a very large moon orbiting a relatively low-mass planet – should produce variations in timing that can be detected in existing data, although non-transiting planets may induce similar signals, complicating exomoon searches.
Astrometry is another promising technique; It is a very precise measurement of the position and motion of an astronomical object in the sky. This could potentially reveal an invisible exomoon offset toward its host’s barycenter, which appears as fluctuations in the planet’s motion around the star. Some interferometers, such as gravity equipment on very large telescope In Chile, one can measure conditions with such astonishing accuracy that it may be possible to detect the wobbles of hidden exomoons, thanks to some giant exoplanets around nearby stars.
In January a team of astronomers described how they used Astrometric measurements of gravity to study HD 206893One star whose companion is HD 206893 b, which is likely a brown dwarf with a mass about 20 times that of Jupiter. Although it is not technically an exoplanet, this brown dwarf may harbor a detectable exomoon. And indeed, the team found some borderline evidence for a companion. If their observed astrometric wobbles are real, it means that HD 206893 b is in a nine-month orbit with something like the predicted mass. about half of Jupiter.
This “moon” would be more than 100 times the mass of Earth – hence the quotation marks – and, like all other exomoon candidates, is as yet unconfirmed. However, astronomers are currently testing a sharp-sighted upgrade to GRAVITY (appropriately called GRAVITY+) that should eventually be able to validate or dismiss this particular candidate.
Yet another exomoon search method involves looking through everything for volcanic activity. This is not as far-fetched as it seems; Jupiter’s moon Io constantly erupts, spewing sulfur into space as its interiors are heated by gravitational tides raised by the giant planet and other nearby moons. In recent years astronomers have used the James Webb Space Telescope (JWST) and other observatories to look at the exoplanet WASP-39b, and they have detected a cloud in its vicinity that contains fluctuating amounts of sulfur dioxide and other compounds. The fluctuations hint at an episodic, external source – potentially an explosion from a type of super-Io satellite that is tidally squeezed by its giant planet host. Finding this—and another similar one, around a different exoplanet, WASP-49AB-is not conclusive, but it shows promise as a new route to finding these elusive exomoons.
And what about exorcism? In some ways, they may be harder to detect than exomoons. The rings, while wide and bright, may actually be quite extraterrestrial; All the material present in Saturn’s rings together forms a sphere about 400 kilometers across, which is equal to the size of its medium-sized moons. Gravitational effects from such trivial instruments would be too small for astronomers to see.
But excursions around a transiting exoplanet can sometimes block enough of the star’s light to register as a series of shallow dips in the star’s light curve. Something like this has already been seen; The star 1SWASP J140747.93-394542.6 (or J1407 for short) displayed a series of extreme dimming events in 2007. One possible explanation is that this dimness was the shadowy transit of a planet, J1407b, surrounded by a giant disk of material. If so, the ring system is vast, possibly 180 million km wide, which is greater than Earth’s distance from the Sun. However, follow-up observations confirmed neither the planet nor its rings, leading astronomers to Other possible explanations.
There may also be another way to detect exorings. In the November 2025 edition of Astronomical Journal, A team of astronomers used JWST to find them. While any of the rings will be too small to see directly, scientists say the icy rings will reflect infrared light strongly at some shorter wavelengths, but not nearly so well at longer wavelengths. If an exoplanet observed by JWST exhibits this pattern, it may be due to the presence of exorings.
The team found that an exoring system would have to be quite large to work because JWST could not detect this effect for any ring system smaller than about three times the extent of Saturn. However, one that was 10 times the size of Saturn could be within reach of the JWST, provided its exoplanet host is not too close to its much brighter star. Scientists also note in their paper NASA’s proposed Habitable Worlds Observatory And the space agency is about to launch soon Nancy Grace Roman Space Telescope Excoring can also be detected in this way.
We have a long way to go before we find an exomoon or exomoons with certainty. But looking at our own giant planets, I suspect these discoveries are a matter of when, not if.
