The Gallic group is a dynamical grouping of the prograde

irregular satellite In astronomy, an irregular moon, irregular satellite, or irregular natural satellite is a natural satellite following an orbit that is irregular in some of the following ways: Distant; inclined; highly elliptical; retrograde. They have often be ...

s of

Saturn Saturn is the sixth planet from the Sun and the second largest in the Solar System, after Jupiter. It is a gas giant, with an average radius of about 9 times that of Earth. It has an eighth the average density of Earth, but is over 95 tim ...

following similar

orbit In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...

s. Their semi-major axes range between 16 and 19 Gm, their

inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Eart ...

s between 36° and 41°, and their eccentricities between 0.46 and 0.53. The

International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...

(IAU) reserves names taken from Gallic mythology for these moons. Similar mean orbital elements led the discoverers to postulate a common origin for the group in a breakup of a larger body. The group was later found to be physically homogeneous, all satellites displaying ''light-red'' colour (

colour indices In astronomy, the color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. The lower the color index, the more blue (or hotter) the object is. Conversely, the larg ...

B − V = 0.91 and V − R = 0.48) and similar

infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

indices. Remarkably, recent observations revealed that the largest member of the group, Albiorix, actually displays two different colours: one compatible with

Erriapus Erriapus , or Saturn XXVIII (28), is a prograde irregular satellite of Saturn. It was discovered by Brett Gladman, John J. Kavelaars and colleagues in 2000, and given the temporary designation S/2000 S 10. It was named Erriapo ...

and Tarvos, and another less red. Instead of the common progenitor, it was postulated that Tarvos and Erriapus could be fragments of Albiorix, leaving a large, less red crater. Such an impact would require a body with the diameter in excess of 1.25 km and relative velocity of 4.79 km/s, resulting in a large crater with the radius of 12 km. Numerous, very large craters observed on Phoebe, prove the existence of such collisions in the Saturnian system's past. The discovery of 20 new moons of Saturn was announced in October 2019 by a team led by Scott S. Sheppard using the

Subaru Telescope is the telescope of the National Astronomical Observatory of Japan, located at the Mauna Kea Observatory on Hawaii. It is named after the open star cluster known in English as the Pleiades. It had the largest monolithic primary mirror in the ...

at Mauna Kea. One of them, S/2004 S 24, is also prograde and of similar inclination, but it orbits much further away from Saturn than the other Gallic moons. This moon will nevertheless also receive a name from Gallic mythology. The seventeen members of the group are (in order of increasing distance from Saturn according to JPL mean orbital elements):

Notes

References

External links

David Jewitt pages
*Ephemeri

*Mean orbital parameter
from JPL
{{DEFAULTSORT:Gallic Group Gallic group Moons of Saturn Irregular satellites Moons with a prograde orbit

See also

Notes

References

External links