Across the outer Solar System and closer to home, a handful of moons carry real atmospheres that change how their surfaces behave, transport heat, and drive chemistry. Studying them gives clues about weather, surface erosion, and where ices or liquids might persist.
There are 10 Moons with Atmospheres, ranging from Callisto to Triton. The table lists each moon with Host planet,Atmosphere (type; main gases),Surface pressure (mbar) — details you’ll find below.
Which moon has the densest atmosphere among these?
Titan tops the list: Saturn’s moon has a thick, nitrogen-rich atmosphere with methane and complex organics that creates weather and surface liquid bodies; its surface pressure exceeds Earth’s, making its atmospheric effects the most Earthlike in the list.
How significant are these atmospheres for surface conditions or exploration?
Even thin envelopes can alter temperatures, drive seasonal transport of volatiles, and produce hazes or sputtering that affect lander design and remote sensing; knowing composition and surface pressure helps prioritize targets for orbiters, landers, or sample missions.
Moons with Atmospheres
| Name | Host planet | Atmosphere (type; main gases) | Surface pressure (mbar) |
|---|---|---|---|
| Titan | Saturn | thick; N2, CH4, H2 | 1,467 |
| Triton | Neptune | tenuous; N2, CH4, CO | 1.40e-02 |
| Io | Jupiter | transient plume; SO2, S2, Na, O | 1.00e-06–1.00e-05 |
| Europa | Jupiter | exosphere; O2, H2O (trace) | 1.00e-09–1.00e-06 |
| Ganymede | Jupiter | exosphere; O2, H2O (trace) | 1.00e-09–1.00e-06 |
| Callisto | Jupiter | exosphere; CO2, O2 (possible) | 1.00e-08–1.00e-05 |
| Enceladus | Saturn | transient plume; H2O, CO2, N2, organics | 1.00e-06–1.00e-03 |
| Rhea | Saturn | exosphere; O2, CO2 | 1.00e-08–1.00e-05 |
| Dione | Saturn | exosphere; O2, CO2 | 1.00e-08–1.00e-05 |
| Tethys | Saturn | exosphere; O2 | 1.00e-09–1.00e-06 |
Images and Descriptions
Titan
Discovered and characterized by Voyager and Cassini flybys and ground-based spectroscopy; Titan’s dense, N2-rich atmosphere with methane and organic chemistry supports weather, clouds, and surface hydrocarbon lakes—the only moon with a thick, stable atmosphere.
Triton
Voyager 2 measured Triton’s thin, N2-dominated atmosphere with trace methane and CO; seasonal nitrogen frost sublimation drives geyser-like plumes and active geology, making Triton the coldest known moon with a confirmed, though very tenuous, atmosphere.
Io
Observed by ground-based telescopes and Galileo, Io’s atmosphere is transient and dominated by SO2 from intense volcanism; localized high-pressure plumes produce stronger, short-lived gas envelopes and drive Io’s colorful surface and magnetospheric interactions.
Europa
Detected by Galileo and Hubble, Europa hosts an ultrathin O2 exosphere produced by surface sputtering of water ice; it lacks a dense air but the oxygen signature signals surface radiolysis and informs habitability studies beneath Europa’s ice shell.
Ganymede
Hubble and Galileo detected a tenuous O2 exosphere around Ganymede tied to sputtering and magnetospheric interactions; though extremely thin, this atmosphere is unique as Ganymede is the only moon with its own magnetosphere influencing atmospheric structure.
Callisto
Galileo and ground-based spectroscopy revealed a very tenuous exosphere with CO2 and possible O2 from surface ice sputtering; Callisto’s sparse atmosphere is notable for weak magnetospheric interaction and its ancient, heavily cratered surface.
Enceladus
Cassini directly sampled Enceladus’s recurring water-vapor plumes with imaging and in-situ mass spectrometry; plume-driven transient atmosphere is water-dominated with organics and salts, indicating a subsurface ocean and making Enceladus a prime astrobiology target.
Rhea
Cassini detected a tenuous O2/CO2 exosphere at Rhea via in-situ and remote measurements, likely from surface sputtering; its sparse atmosphere hints at surface composition and interactions with Saturn’s magnetospheric particles.
Dione
Cassini measurements found a very thin O2/CO2 exosphere around Dione produced by sputtering of surface ice; though minute, this atmosphere helps trace surface composition and plasma interactions in Saturn’s system.
Tethys
Cassini detected an ultrathin O2 exosphere at Tethys through UV occultations and mass spectrometry; produced by sputtering, the atmosphere is negligible for pressure but important for understanding surface chemistry and magnetospheric processes.
