Enceladus
Reference data for Saturn's moon Enceladus: 1.37-day resonant orbit, 504 km diameter, south-polar Tiger Stripe plumes, and astrobiology metrics.
Provenance-Backed Scientific Measurements
Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.
| Parameter | Value | Uncertainty | Method & Epoch | Quality Status | Source Archive |
|---|---|---|---|---|---|
| Opposition Magnitude (V) | 11.7 mag | ± 0.15 mag | JPL Horizons DE440/441 planetary and satellite ephemeris solution | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Sidereal Orbital Period | 1.370218 d | ± 0.000001 d | 32.885 hours; locked in a 2:1 mean-motion resonance with Dione. | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Kronocentric Semi-Major Axis | 0.001591 AU | ± 0.000001 AU | Orbits 238,042 km (3.95 Saturn radii) from Saturn's center, embedded inside the diffuse E ring. | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Mean Volumetric Radius | 0.0396 R⊕ | ± 0.0001 R⊕ | Mean radius of 252.1 ± 0.2 km (diameter 504.2 km—roughly the width of Great Britain). | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Mass | 0.0000181 M⊕ | ± 1e-7 M⊕ | 1.08022 × 10²⁰ kg. | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Mean Surface Temperature | 75 K | ± 10 K | Equatorial plains average ~75 K, whereas south-polar Tiger Stripe fractures exceed 180 K. | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Enceladus (Saturn II) — Ocean World & Plume Data at RA 05h 30m 00.00s, Dec +21° 50′ 00.0″ within Taurus, alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.
Astrophysical Context & Structure
Discovered on August 28, 1789, by William Herschel during his first observations with his newly completed 40-foot (1.2-meter) reflector at Slough, Enceladus (Saturn II) is a diminutive world only 504.2 kilometers in mean diameter orbiting 238,042 kilometers from Saturn every 32.89 hours. Because a constant snowfall of fresh micron-sized water-ice grains coats its surface, Enceladus boasts a geometric visual albedo of 1.38 and a Bond albedo of 0.81—reflecting more incident sunlight than any other body in the Solar System and keeping its midday equatorial surface near a frigid 75 K.
A 2:1 orbital resonance with outer moon Dione maintains Enceladus's slight orbital eccentricity (e = 0.0047), tidally heating its interior above a porous silicate core. In 2005, NASA's Cassini spacecraft discovered over 100 supersonic cryovolcanic geysers erupting along four warm, parallel tectonic fractures at the south pole—dubbed the 'Tiger Stripes' (Alexandria, Cairo, Baghdad, and Damascus Sulci). Shooting ~200 kilograms per second of water vapor and ice grains into space at over 1,400 kilometers per hour, these plumes continuously replenish Saturn's sprawling E ring.
Measurements of Enceladus's physical libration (wobble) confirmed that its ice shell floats completely detached atop a global subsurface ocean 30 to 40 kilometers deep. By flying directly through the south-polar plumes, Cassini's mass spectrometers and dust analyzers detected sodium salts, molecular hydrogen (H₂), methane, complex macromolecular organics, nanometer-sized silica grains formed at >90 °C alkaline hydrothermal vents, and bio-essential sodium phosphates—making Enceladus one of the premier astrobiological targets in the Solar System.
Practical Visual Observing Guide
- Although Enceladus shines at V = 11.7 at opposition, it orbits just 38 arcseconds from Saturn's center (barely outside the A ring), so ring glare makes it a challenging target requiring an 8-inch to 12-inch telescope.
- Easiest to spot at greatest eastern or western elongation (~20 arcseconds off the ring tips) or during Saturn ring-plane crossing seasons when ring glare is minimal.
- Using an occulting bar in the eyepiece to block Saturn's bright globe dramatically improves visual visibility.
Catalog Cross-Identifications & Aliases
Common Aliases: Saturn II · E-Ring Cryovolcanic Moon
| Catalog Authority | Identifier |
|---|---|
| SIMBAD | Enceladus |
Related Objects, Comparisons & Guides
Titan (Saturn VI Nitrogen-Atmosphere Moon)
Orbital parameters (15.945 d around Saturn), visual magnitude 8.4, 1.45-bar N2/CH4 atmosphere, hydrocarbon lakes, and observing guide for Titan.
Saturn (Ringed Giant & Cassini Division)
JPL orbital parameters (9.5826 AU, 29.457 yr), ring tilt cycle, Cassini Division resolution, and telescope observing guide for Saturn.
Europa (Jupiter II Subsurface Ocean World)
Orbital parameters (3.551 d around Jupiter in 1:2:4 Laplace resonance), magnitude 5.29, icy shell & subsurface ocean, and observing guide for Europa.
Apparent vs Absolute Magnitude Explained
Understand the logarithmic Pogson astronomical magnitude scale, apparent visual magnitude (m), absolute magnitude (M at 10 parsecs), and bolometric corrections.
Angular Size, Separation & Field of View
How angular diameter (degrees, arcminutes, arcseconds), spherical angular separation, and small-angle physical diameter relate to telescope field of view.
Scientific Sources & Dataset Provenance
- NASA/JPL Solar System Dynamics & Planetary Fact Sheets (DE441 (2021/2026)): Park, R. S., et al. 2021, AJ, 161, 105 (The JPL Planetary and Lunar Ephemerides DE440 and DE441) — NASA Jet Propulsion Laboratory / GSFC