Enceladus Brightens Its Sister Moons With Snow

 In the cold twilight of the outer Solar System, the beautiful ringed planet Saturn and its myriad moons orbit our Sun in frigid splendor. Enceladus is an intermediate-size moon of Saturn, and it harbors a sloshing subsurface ocean of liquid water well-hidden beneath its crust of ice. The moons of Saturn are diverse and numerous, ranging in size from tiny moonlets that are less than a kilometer across to the hydrocarbon-slashed enormous moon Titan, which is larger than the planet Mercury. But little Enceladus stands out in the crowd because of its subsurface global ocean, which suggests the possibility--though by no means the promise--that aquatic life swims around in the dark hidden waters beneath its shell of ice. In September, 2019, a team of planetary scientists announced that radar observations of Saturn's intermediate-size moons, Mimas, Enceladus, and Tethys, reveal that Enceladus is spraying out a snow storm that coats both itself and its two sister moons with fresh, sparkling water-ice particles.


This sparkling snow storm causes an extreme radar brightness that also suggests the hidden presence of "boomerang" structures lurking beneath the surface of Enceladus. These structures enhanced the moon's efficiency in returning microwave signals to the visiting Cassini spacecraft. The results of the new study were presented by Dr. Alice Le Gall at the 2019 European Planetary Science Congress (EPSC)-American Astronomical Society (AAS) Division of Planetary Science (DPS) Joint Meeting held in Geneva Switzerland. Dr. Le Gall is of the Laboratoire-Atmospheres-Mileux, Observations Spataiales (LATMOS), Sorbonne University (UNSQ), in Paris, France.


Dr. Le Gall and her team of researchers from France and the United States have analyzed 60 radar observations of Saturn's inner icy moons, using the full database of observations taken by the Cassini mission between 2004 and 2017. They found that earlier reporting on these observations had underestimated the radar brightness by a factor of two. Cassini's mission to the Saturn system ended in 2017.


Enceladus displays a chemical composition that is similar to that of comets--and it also hurls out jets of gas and dust, which provide a valuable clue that liquid water is secreted beneath its frozen surface.


The Sparkling Dance Of The Icy Moons


Saturn has 62 known moons with confirmed orbits around their giant parent-planet--53 of which have been named, while only 13 sport diameters greater than 50 kilometers. Saturn is also famous for its magnificent system of rings that display complex orbital motions all their own. Several of Saturn's moons are large enough to be ellipsoidal in shape. However, only two of those--Titan and Rhea--are presently in hydrostatic equilibrium.


Two dozen of Saturn's moons are classified as regular satellites. This means that they travel around Saturn in prograde orbits that are not greatly inclined in Saturn's equatorial plane. This collection of regular Saturnian moons include seven major moons, a quartet of smaller moons that travel in trojan orbits along with their larger sibling moons, a duo of mutually co-orbital moons, and two other moons that function as shepherds in Saturn's F ring. Another duo of regular moons orbit within the gaps of Saturn's mesmerizing rings. The relatively large icy moon Hyperion is trapped in a resonance with Titan. The remaining regular moons orbit close to the outer edge of the A ring, within the G ring, and between Mimas and Enceladus. The regular moons are traditionally named after Titans and Titanesses or other mythical figures associated with the Roman god Saturn (Greek, Cronus).


The remaining 38 Saturnian moons sport mean diameters between 4 and 213 kilometers, and are classified as irregular moons. This batch of irregular moons travel on orbits that are very far from Saturn, and also display high inclinations. These irregular Saturnian moons show a mix of prograde and retrograde orbits around their parent-planet. They are thought to be either minor planets, or tattle-tale debris left over from the disintegration of minor planets following their gravitational capture by Saturn. In this way, the shattered remnants of minor planets create collisional families of objects in orbit around Saturn. The irregular satellites have been classified according to their differing orbital attributes into the Gallic, Inuit, and Norse family groups. Phoebe is the largest of Saturn's irregular moons, and it was discovered at the end of the 19th century.





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