It is approximately concentric with Odysseus—a pole of Ithaca Chasma lies only approximately 20° from the crater. Image credit: NASA/JPL/SSI.
[30][31], In May 2013, it was announced that NASA's spacecraft Cassini had provided scientists with evidence that Dione is more active than previously realized. [47] The cooling near-surface layer contracted and the interior expanded. Tethys and Dione This natural color, time-lapse movie comprised of images from the Cassini spacecraft taken in December 2010 shows Dione moving from left to right, passing behind its sister moon Tethys, which remains in the center of the frame. The dimensions of this ellipsoid are consistent with it having a homogeneous interior.
The Eurotas (top) and Palatine Chasmata run from upper right to lower left; the Padua Chasmata are near vertical at right, and the Carthage Fossae horizontal at left.
It was discovered by Italian astronomer Giovanni Domenico Cassini in 1684. [39], The density of impact craters varies across the surface of Tethys.
The image scale is approximately 15 kilometers (9 miles) per pixel. 42–43, "Cassini Observes the Active South Pole of Enceladus", "Cassini Finds Hints of Activity at Saturn Moon Dione", Overlooked Ocean Worlds Fill the Outer Solar System, "Another Saturn Moon May Hide Subsurface Ocean", "Detection of Exospheric O2+ at Saturn's Moon Dione", "Magnetic signatures of a tenuous atmosphere at Dione", "Cassini Views Dione, a Frigid Ice World", Cassini Doubleheader: Flying By Titan and Dione (April 2010), "Cassini Sends Back Views After Zooming Past Dione", "Cassini to Make Last Close Flyby of Saturn Moon Dione", Spacecraft Makes Final Close Flyby of Saturn Moon Dione Today, Images of Dione at JPL's Planetary Photojournal, https://en.wikipedia.org/w/index.php?title=Dione_(moon)&oldid=975859530, Creative Commons Attribution-ShareAlike License, This page was last edited on 30 August 2020, at 20:10.
These revealed that the 'wisps' were, in fact, not ice deposits at all, but rather bright ice cliffs created by tectonic fractures (chasmata). Tethys is locked in an inclination resonance with Mimas, however due to the low gravity of the respective bodies this interaction does not cause any noticeable orbital eccentricity or tidal heating. [17] Downward bending of the surface associated with the 1.5 km high ridge Janiculum Dorsa can most easily be explained by the presence of such an ocean. [33] Temperature maps of Tethys obtained by Cassini, have shown this bluish region is cooler at midday than surrounding areas, giving the satellite a "Pac-man"-like appearance at mid-infrared wavelengths. In this case Ithaca Chasma would be the outermost ring graben of Odysseus. Original Source: NASA/JPL/SSI News Release, Join our 836 patrons! [34], The surface of Tethys mostly consists of hilly cratered terrain dominated by craters more than 40 km in diameter. "Saturn IV" redirects here. [41], Tethys is thought to have formed from an accretion disc or subnebula; a disc of gas and dust that existed around Saturn for some time after its formation.
[16] By the end of the seventeenth century, astronomers fell into the habit of referring to them and Titan as Saturn I through Saturn V (Tethys, Dione, Rhea, Titan, Iapetus). Because Dione is relatively small, an impact causing a 35 kilometer crater could have spun the satellite. Tethys is named after the titaness Tethys. The density of Tethys is 0.98 g/cm³, indicating that it is composed almost entirely of water-ice. However, reflecting Saturn's greater mass (95 times that of Earth's), Dione's orbital period is one tenth that of the Moon. The Cassini orbiter performed a closer flyby of Dione at 500 km (310 mi) on October 11, 2005, and captured oblique images of the cliffs, showing that some of them are several hundred metres high. The huge impact structure Odysseus (450 kilometers, or 280 miles across) is near the limb of Tethys. [6] Its mass is 6.17×1020 kg(0.000103 Earth mass),[7] which is less than 1% of the Moon. [11] The satellites of Saturn were not named until 1847, when William Herschel's son John Herschel published Results of Astronomical Observations made at the Cape of Good Hope, suggesting that the names of the Titans (sisters and brothers of Cronus) be used. Because there are many craters larger than 35 kilometres (22 mi), Dione could have been repeatedly spun during its early heavy bombardment. Using topographic data, NASA teams deduced that crustal depression associated with a prominent mountain ridge on the leading hemisphere is best explained if there was a global subsurface liquid ocean like that of Enceladus. 12:59 Why can gas giants remain spherical? And More… With Astronaut Terry Virts, Episode 680: Interview with Fraser on Awesome Astronomy, Episode 679: Q&A 127: Does the Simulation Hypothesis Explain the Fermi Paradox?
Dione has two co-orbital, or trojan, moons, Helene and Polydeuces.
[35], The Cassini spacecraft entered orbit around Saturn in 2004. This coloration and darkening of the Tethyan surface is typical for Saturnian middle-sized satellites. At 1122 km (697 mi) in diameter, Dione is the 15th largest moon in the Solar System, and is more massive than all known moons smaller than itself combined.
[42] The low temperature at the position of Saturn in the Solar nebular means that water ice was the primary solid from which all moons formed. Cassini found Dione in 1684 using a large aerial telescope he set up on the grounds of the Paris Observatory.
[18][19] Gravity and shape data points to a 99 ± 23 km thick ice shell crust on top of a 65 ± 30 km thick internal liquid water global ocean. [24], Dione was first imaged by the Voyager space probes. This hypothesis was proven wrong by the Cassini probe flyby of December 13, 2004, which produced close-up images. [24][25] The density of molecular oxygen ions determined from the Cassini plasma spectrometer data ranges from 0.01 to 0.09 per cm3. Of April 22 st. N. 1686. 19:40 Could we use interstellar hydrogen as fuel? The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The band has an elliptical shape getting narrower as it approaches the trailing hemisphere. Saturn’s moon Dione occults part of Saturn’s distant rings while Tethys hovers below. A Key Biosignature Called Phosphine has been Discovered in Venus' Atmosphere, Episode 681: Q&A 128: Which Supernova Created the Solar System? The latter can be a result of focusing the seismic waves produced by the impact in the center of the opposite hemisphere. [12], Dione orbits Saturn with a semimajor axis about 2% less than that of the Moon. It was discovered by G.D. CASSINI in 1684, the year in which he also discovered its outer neighbour, DIONE. The plains have a relatively sharp boundary with the surrounding cratered terrain. [13] The resonance also maintains a smaller eccentricity in Dione's orbit (0.0022), tidally heating it as well.[14]. Dione features linear 'virgae' that are up to hundreds of km long but less than 5 km wide. [14] Once Mimas and Enceladus were discovered in 1789 by William Herschel, the numbering scheme was extended to Saturn VII by bumping the older five moons up two slots. However the smooth appearance of the plains together with their sharp boundaries (impact shaking would have produced a wide transitional zone) indicates that they formed by endogenic intrusion, possibly along the lines of weakness in the Tethyan lithosphere created by Odysseus impact. Dione is currently in a 1:2 mean-motion orbital resonance with moon Enceladus, completing one orbit of Saturn for every two orbits completed by Enceladus. The heavily cratered terrain has numerous craters greater than 100 kilometres (62 mi) in diameter.
The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. It is more than 2000 km in length, approximately 3/4 of the way around Tethys' circumference. The most probable candidate is nanophase iron or hematite. Older impact craters are somewhat shallower than young ones implying a degree of relaxation. There was a close targeted flyby, at a distance of 500 km (310 mi) on 11 October 2005;[27] another flyby was performed on 7 April 2010 also at a distance of 500 km.
It has also been probed five times from close distances by the Cassini orbiter. Tethys is also subject to constant bombardment by the energetic particles (electrons and ions) present in the magnetosphere.[22]. https://www.youtube.com/channel/UC0-KklSGlCiJDwOPdR2EUcg/, Astronomy Cast:
A comparable band exists only on Mimas. Only Odysseus crater has a central depression resembling a central pit.
[>>>] Post was not sent - check your email addresses! [10] It is named after the Titaness Dione of Greek mythology. They are brighter than everything around them and appear to overlay other features such as ridges and craters, indicating they are relatively young.
However, if it is differentiated, the radius of the core does not exceed 145 km, and its mass is below 6% of the total mass.
Tethys was discovered by Giovanni Domenico Cassini in 1684 together with Dione, another moon of Saturn. Dione's icy surface includes heavily cratered terrain, moderately cratered plains, lightly cratered plains, and areas of tectonic fractures. Want to be part of the questions show? Of April 22 st. N. 1686. [52][54][55], Another flyby of Tethys took place on 14 August 2010 (during the solstice mission) at a distance of 38,300 km, when the fourth-largest crater on Tethys, Penelope, which is 207 km wide, was imaged. Did Iapetus Consume One of Saturn’s Rings?
See no ads on this site, see our videos early, special bonus material, and much more. Panorama with fractures (the Palatine Chasmata) near limb, bisecting craters Euryalus (right) and Nisus just left of center. The pattern of cratering since then and the bright albedo of the leading side suggests that Dione has remained in its current orientation for several billion years. Close flyby of Dione reveals a highly cratered surface. [18][32][33] The ridge Janiculum Dorsa has a height of 1 to 2 km (0.6 to 1.2 miles); Dione's crust seems to pucker 0.5 km (0.3 miles) under it, suggesting that the icy crust was warm when the ridge formed, probably due to the presence of a subsurface liquid ocean, which increases tidal flexing.[34].