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Moon

Prometheus

Prometheus is an irregular moon of Saturn in the vicinity of the narrow F ring. Its gravity disturbs inner ringlets, producing channels and filamentary structures; together with Pandora, it is described as shepherding the ring.

Verified 2026-10-02

Overview

Identity and classification

Prometheus is identified in the supplied evidence as a moon of Saturn with a distinctly irregular shape. NASA uses an informal comparison to a “sweet potato,” while another account calls it potato-shaped. These expressions do not provide a full geometric model, but they do show that the body is not treated as approximately spherical. It occupies the environment of Saturn’s narrow, structurally complex F ring, and its connection with that ring is the best documented physical and dynamical feature in the available material.

Size, surface, and measured properties

The sources do not give one mutually consistent transverse size. Several NASA and ESA items state 102 kilometers across, whereas one ESA description calls Prometheus an 86-km-wide moon and a NASA resource uses 86 kilometers for the F-ring-perturbing object. The evidence therefore does not support selecting a single dimension without reporting the conflict. NASA further states that the visible surface has craters, some as large as 20 kilometers in diameter, and that Prometheus is much less cratered than nearby Pandora, Janus, and Epimetheus. This is an observational comparison of surface appearance, not a quantified surface age.

No supplied source gives mass, volume, density, gravity, albedo, temperature, mineral or ice composition, or internal structure. Nor do the excerpts document an atmosphere, exosphere, geological activity, or specific surface landforms beyond craters and irregular shape. Composition and interior history consequently cannot be inferred from this evidence set.

Orbit and the F-ring interaction

Prometheus orbits Saturn immediately near the F ring. NASA places Prometheus inside the F ring and Pandora outside it; ESA says that the two moons shepherd the narrow ring. Shepherding here is evidenced as gravitational interaction with ring particles and ringlets, not as a solid boundary. NASA specifically reports that Prometheus gravitationally interacts with the inner flanking ringlets of the F ring, making dark channels as it passes.

The evidence attributes periodically produced streamer-channels and intricate formations in the thin F ring to Prometheus’s gravity. A Cassini observation followed the moon around the rings during a complete azimuthal scan, supplying observational context for connecting its passage with those structures. ESA also reports that Prometheus overtakes Pandora in orbit roughly every 25 days. The supplied material gives no orbital period, semimajor distance, eccentricity, inclination, or rotational period and direction.

Setting and exploration

The documented local setting includes the F ring, Pandora, Atlas, Epimetheus, and Janus. In one NASA description, Prometheus and Atlas are the two moons interior to the F ring; Pandora and Epimetheus are exterior, and Janus is visible in the same sequence. The available imagery and explanatory material come from, or refer to, Cassini. NASA notes that four spacecraft visited the Saturn system, but that Cassini alone orbited Saturn. ESA describes an image acquired during a Cassini dive between Saturn and its rings from about 1.1 million km from Saturn, within the context of the mission’s 13-year Saturn-system odyssey.

Scientific importance and limits

Prometheus matters scientifically because it offers visible evidence that the gravity of a small, non-spherical moon can organize structures in a narrow ring. The repeated association between its passage and F-ring channels is the strongest conclusion supported by these excerpts. By contrast, the moon’s formation, collisional evolution, composition, internal structure, spin state, and the reason for the 86-versus-102-km discrepancy remain unresolved here. The supplied sources also do not provide a discovery date, image-by-image instrument details, or enough numerical orbital and physical parameters for a comprehensive model.

Essential data

Key fact
interactive_moon
Key fact
saturn-prometheus
Key fact
537

Physical properties

Diameter
86.2
Measurement
0.4784
Measurement
0.01071

Orbital data

Values include their timeframe and uncertainty when available. This view does not simulate real-time positions.

Semi-major axis
139400
Parameter
0.615878

Dates and timeline

Historical year
1980

Sources and references

  1. Catálogo astronómico del visualizador Catálogo astronómico del visualizador
  2. Saturn Moons: Facts NASA
  3. Atlas - NASA Science NASA
  4. Cassini: Saturn's Moons NASA
  5. Prometheus - NASA Science NASA
  6. ESA - Saturn’s rings and Prometheus European Space Agency
  7. Moon and its Flock - NASA Science NASA
  8. Moon and Its Handiwork - NASA Science NASA
  9. Prometheus' Trail - NASA Science NASA
  10. Atlas Found! - NASA Science NASA
  11. ESA - Pandora, Prometheus and Epimetheus European Space Agency