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 a distant, orbital inclination, inclined, and often orbital eccentricity, eccentric and Retrograde and prograde motion, retrograd ...

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 nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...

following similar

orbit In celestial mechanics, an orbit 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 object or position in space such as a p ...

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 Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object ...

s between 35° and 40°, and their eccentricities around 0.53. The

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...

(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 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 those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

indices Remarkably, recent observations revealed that the largest member of the group, Albiorix, displays actually two different colours: one compatible with Erriapus 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.Grav, Tommy; and Bauer, James; ''A deeper look at the colors of Saturnian irregular satellites'',
Preprint
/ref> Such an impact would require a body with the diameter in excess of 1 km and relative velocity close to 5 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 wo ...

at Mauna Kea. One of them,

S/2004 S 24 S/2004 S 24 is a natural satellite of Saturn, and the outermost known prograde satellite. Its discovery was announced by Scott S. Sheppard, David C. Jewitt, and Jan Kleyna on October 7, 2019 from observations taken between December 12, 2004 and ...

, is also prograde, but it orbits much further away from Saturn than the four known Gallic moons. This moon will nevertheless also receive a name from Gallic mythology.Saturn surpasses Jupiter after the discovery of 20 new moons—and you can help name them
NASA, phys.org, October 7, 2019 The four members of the group discovered before 2019 are (in order of increasing distance from Saturn): * Albiorix * Bebhionn *

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 in ...

* Tarvos

References

*Ephemeri
from MPC
*Mean orbital parameter
from JPL

External links

{{DEFAULTSORT:Gallic Group Gallic group Moons of Saturn Irregular satellites Moons with a prograde orbit

See also

References

External links