Space · Moons
Phoebe
A moon of Saturn — Saturn's largest irregular moon — a captured Kuiper Belt object orbiting backward at extreme distance.
Quick facts
Parent planet
Diameter (mean)
213 km
Mass
8.29 × 10¹⁸ kg
0.0001128 Moon masses
Mean orbital radius
12,952,000 km
Orbital period
550.6 Earth days
Discovery year
1899
Discoverer
William Henry Pickering
Naming origin
Titaness, grandmother of Apollo
Surface conditions
Phoebe orbits Saturn retrograde at a great distance (13 million km), and its dark, water-rich composition and isotope ratios identify it as a captured body from the Kuiper Belt or scattered disk — a fragment of the outer solar system held permanently by Saturn's gravity. Cassini's June 2004 flyby of Phoebe en route to Saturn-orbit insertion produced the only resolved imagery; the dark material seen on Iapetus's leading hemisphere is thought to originate from Phoebe and be slowly transported inward.
Phoebe is the source of the largest known ring in the solar system — the Phoebe ring, a tenuous disk of dust extending from 128 to 207 Saturn radii, only detected in 2009 by Spitzer Space Telescope infrared observations.
Missions and observations
Every Saturn-system mission has had an opportunity to image or characterize Phoebe. The list below is the Saturn-system mission catalog; specific Phoebe encounters are documented in mission archives.
| Mission | Year at Saturn | Status |
|---|---|---|
|
Pioneer 11 NASA |
1979 | Completed |
|
Voyager 1 NASA |
1980 | Completed |
|
Voyager 2 NASA |
1981 | Completed |
|
Cassini-Huygens NASA/ESA/ASI |
2004 | Completed |
|
Dragonfly NASA |
2034 | On the way |
Naming etymology
Phoebe was a Titaness, daughter of Uranus and Gaia, grandmother of Apollo and Artemis via her daughter Leto. William Pickering discovered the moon photographically from Harvard in 1899 — the first solar-system moon found by photographic plate rather than direct visual observation. Named in 1900.
Methodology & sources
Diameter, mass, and orbital parameters from JPL Solar System Dynamics — Physical Parameters. Discovery year and discoverer from the JPL Satellite Discovery Circumstances. Naming etymology from the IAU Working Group for Planetary System Nomenclature. Stylized SVG hero composed from NASA / JPL imagery as visual reference; no photographs are reproduced.