Moon
Tethys
Tethys is Saturn’s fifth-largest moon, a cold, airless and heavily impact-scarred body globally mapped with Cassini images.
Overview
Identity and scale
Tethys is a moon of Saturn and, according to NASA, the planet’s fifth-largest moon. The supplied evidence describes it as irregularly shaped, cold, airless, and heavily scarred by impacts. Its mean radius is given as 331 miles, or 533 kilometres. Published dimensions are 669 × 657 × 654 miles, equivalent to 1076.8 × 1057.4 × 1052.6 kilometres. A Cassini image caption gives a diameter of about 1,071 kilometres. Since Tethys is not spherical, these values need not represent the same geometric measurement; the evidence does not establish one of them as the sole definitive diameter.
NASA describes Tethys as very similar to its sister moons Dione and Rhea. The available excerpts do not state which measured properties underlie that comparison. It is therefore useful context, but not evidence that the three moons have identical compositions, internal structures, or evolutionary histories.
Surface features and geological inferences
The observed surface includes the immense crater Odysseus, stated to be about 450 kilometres across. Cassini imagery shows its central mountain in relief, as well as many smaller impact sites. The reported abundance of craters and NASA’s description of Tethys as heavily scarred establish impact modification as a major visible feature of the terrain. Another defining structure is Ithaca Chasma, a major fracture reported by ESA, from Voyager images, as about 750 kilometres long. NASA compares its extent to four times the length of Earth’s Grand Canyon. The supplied material provides neither its width, depth, age, nor a demonstrated formation mechanism.
A NASA presentation says that the large crater nearly circles the moon and notes an interpretation: the impact that formed it did not disrupt Tethys, which has been taken as evidence that Tethys was not completely frozen in its past. This is an inference, rather than a direct measurement of the interior or proof of a former liquid state. No absolute surface ages, thermal history, density, mass, or internal-layer model is provided by the evidence.
Colour, illumination, orbit, and environment
Cassini observed mysterious reddish arcs on Tethys. NASA notes that they were difficult to see until a Cassini scientist examined the surface in near-infrared light, where the arcs became conspicuous. This shows that the surface’s appearance depends on observing wavelength. It does not, from the supplied material, identify the responsible substance, the arcs’ origin, their global distribution, or their age.
One Cassini view identifies the lit terrain as part of Tethys’s leading hemisphere as it orbits Saturn. Another explains that vertical relief on solid Solar System bodies is often easiest to discern near the terminator. These statements document viewing geometry and an observational constraint, not orbital parameters. No orbital period, orbital distance, eccentricity, inclination, rotation period, or explicit tidal-locking statement appears in the evidence. Nor do the sources supplied document rings, satellites of Tethys, or a measurable atmosphere; the supported characterization is that it is airless.
Exploration, mapping, and remaining questions
Voyager images revealed the large fracture. ESA stated that Cassini would investigate it and other features during two planned flybys, the first on 24 September 2005. Cassini imagery was subsequently used for a USGS Astropedia global mosaic listed at 293-metre resolution. The Cassini Imaging Team also created a high-resolution atlas: 15 quadrangle map sheets covering the entire surface at a nominal 1:1,000,000 scale. Such mapping is a major observational resource, but global coverage does not by itself resolve subsurface structure or composition.
Tethys is scientifically significant because it preserves the visible record of giant impacts, long fractures, and subtle near-infrared colour anomalies on a cold Saturnian moon. Important unresolved issues remain: the composition and cause of the red arcs; the origin of Ithaca Chasma; the internal properties implied by survival of the Odysseus-forming impact; and whether the suggested geological activity of Tethys and Dione was confirmed. The evidence only reports that a Cassini press release suggested possible activity, not that it was established. Formation, thermal evolution, detailed composition, and orbital dynamics remain outside the limits of the supplied sources.
Essential data
- Key fact
- interactive_moon
- Key fact
- saturn-tethys
- Key fact
- 526
Physical properties
- Diameter
- 1062.2
- Measurement
- 0.984
- Measurement
- 41.21353
Orbital data
Values include their timeframe and uncertainty when available. This view does not simulate real-time positions.
- Semi-major axis
- 295000
- Parameter
- 1.887802
Dates and timeline
- Historical year
- 1684
Sources and references
- Catálogo astronómico del visualizador Catálogo astronómico del visualizador
- Tethys - NASA Science NASA
- In Depth | Tethys – NASA Solar System Exploration NASA
- ESA - Saturn's moon Tethys European Space Agency
- Approaching Titan and Tethys - NASA Science NASA
- APOD: 1995 November 24 - Saturn's Moon Tethys - NASA Science NASA
- Astropedia - Tethys Cassini Global Mosaic 293m USGS Astrogeology Science Center
- The Tethys Atlas | NASA Jet Propulsion Laboratory (JPL) NASA
- Saturn Moons: Facts NASA
- Texture of Tethys - NASA Science NASA
- The Tethys Atlas - NASA Science NASA