01 / MARSOBSERVED SURFACE · OPEN QUESTION
Phobos
A moon with a scar nearly its own size.
Stickney crater dominates this small, irregular moon. Its long grooves are real; how all of them formed is still debated.
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ATLAS / MOONS
Worlds around worlds.
Twelve moons. Twelve reasons to look again. Oceans beneath ice, fire across rock, and one little world that tumbles without keeping time.Begin the journey ↓01 — 12 / A CURATED FIELD GUIDE
Twelve moons to explore.
These are spacecraft observations, not imagined portraits. Where an ocean or an interior process is inferred rather than directly seen, we say so.
02 / JUPITEROBSERVED ACTIVITY
Io
The most volcanic world we know.
Jupiter's gravity and its neighbouring moons knead Io's interior. Spacecraft have witnessed eruptions and a surface continually repainted by volcanism.
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03 / JUPITEROBSERVED ICE · INFERRED OCEAN
Europa
An ocean concealed by ice.
Galileo saw a fractured icy shell. Multiple lines of evidence point to a salty ocean below it; Europa Clipper will investigate whether the moon has conditions that could support life.
View original image and context Follow Europa Clipper →
04 / JUPITEROBSERVED FIELD · INFERRED OCEAN
Ganymede
A moon with its own magnetic field.
The Solar System's largest moon generates a magnetic field and is thought to hide a saltwater ocean. ESA's Juice mission will study it in remarkable detail.
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05 / JUPITEROBSERVED CRATERS · POSSIBLE OCEAN
Callisto
A surface that remembers impacts.
Heavily cratered and ancient-looking, Callisto holds a long record of collisions. Magnetic measurements suggest a salty ocean may lie far beneath its battered exterior.
View original image and contextOFFICIAL FILM · ESA / JUICE
Three icy moons. One extraordinary journey.
ESA's one-minute introduction connects Europa, Callisto and Ganymede to the mission designed to explore them.Film and context · ESAPoster: Ganymede · NASA/JPL-Caltech/SwRI/MSSS. Film: ESA - European Space Agency.
06 / SATURNOBSERVED LANDSCAPES · FUTURE EXPLORATION
Titan
Rivers and lakes, but not of water.
Cassini–Huygens revealed a world with a thick atmosphere and a methane cycle. Dragonfly will investigate its surface chemistry and landscape.
View original image and context Enter Titan →
07 / SATURNOBSERVED PLUMES · INFERRED INTERIOR
Enceladus
An ocean that reaches into space.
Cassini photographed jets escaping from fractures near the south pole and sampled their material. The plumes reveal a global ocean and evidence of hydrothermal activity below the ice—not evidence of life itself.
Cassini took these views one day apart at similar distances. Facing the Sun, the ice shines. Seen nearly against it, the south-polar spray becomes visible. Different viewing angles—not a sudden eruption.
View original image and context Watch Cassini's plume sequence · NASA
08 / SATURNOBSERVED SURFACE
Mimas
A moon dominated by Herschel crater.
Herschel crater spans a striking fraction of this little moon.
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09 / SATURNOBSERVED CONTRAST · OPEN QUESTION
Iapetus
Two faces and a mountain-like seam.
One hemisphere is dark, the other bright. An immense equatorial ridge makes Iapetus stranger still, while the ridge's origin remains unresolved.
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10 / SATURNOBSERVED SURFACE · CHAOTIC ROTATION
Hyperion
A moon with chaotic rotation.
Cassini saw a pitted, sponge-like surface. Hyperion tumbles chaotically as it circles Saturn: unlike most large moons, it does not present a predictable face.
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11 / URANUSOBSERVED TERRAIN · OPEN QUESTION
Miranda
A patchwork world.
Voyager 2 revealed towering scarps and wildly different terrains stitched together on one small moon. The history behind that geology is still debated.
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12 / NEPTUNEOBSERVED ORBIT · OBSERVED PLUMES
Triton
A moon orbiting against Neptune’s rotation.
Triton orbits opposite Neptune's rotation. Voyager 2 also saw dark plumes rising above its icy surface.
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