300px|thumb|Animation of Saturn's Gallic group of satellites
thumb|upright=1.5|268 irregular moons of Saturn plotted by semi-major axis and inclination . The Gallic group is the yellow cluster of moons on the right, with the outlier [[S/2004 S 24 colored green.]]
The Gallic group (or family or cluster; also referred to as the first inclination group, the 34° inclination cluster, or the Gaulish cluster The International Astronomical Union (IAU) reserves names taken from Gallic mythology for these moons, though only four of them have names at present.
Characteristics
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 indices.
Later observations revealed that the largest member of the group, Albiorix, actually displays two different colours: one compatible with Erriapus and Tarvos, and another less red. Rather than directly originating from the common progenitor, it was postulated that Tarvos and Erriapus could instead 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 a radius of 12 km. Numerous, very large craters observed on Phoebe (an irregular moon in the Norse group) prove the existence of such collisions in the Saturnian system's past.
There is also a theory that the progenitor moon suffered a head-on collision, which could explain some trends in the orbital elements of the Gallic group. The orbital parameters are fairly compact; the semi-major axes mostly range between 16 and 19 million km, their inclinations between 36° and 41°, and their eccentricities between 0.46 and 0.53. Within the Gallic group, relative to Albiorix, all other moons orbit at a larger distance, and almost all of them have greater inclinations. The eccentricity somewhat increases with semi-major axis.
List
The 19 members of the group are (in order by date announcement):
|-id=Tarvos <!-- S/2000 S 4 --> bgcolor=#fdf
|Tarvos || 16 || || 926.43 || Albiorix
|-id=Erriapus <!-- S/2000 S 10 --> bgcolor=#fdf
|Erriapus || 12 || || 871.09 || Albiorix
|-id=Albiorix <!-- S/2000 S 11 --> bgcolor=#fdf
|Albiorix || 28.6 || || 783.46 || Albiorix
|-id=Bebhionn <!-- S/2004 S 11 --> bgcolor=#fdf
|Bebhionn || 7 || || 834.85 || Albiorix
|-id=S/2004_S_24 bgcolor=#dfd
|S/2004 S 24 || 3 || || 1341.34 || Outlier
|-id=S/2004_S_29 bgcolor=#fdf
|S/2004 S 29 || 5 || || 837.78 || Albiorix
|-id=S/2020_S_4 bgcolor=#fdf
|S/2020 S 4|| 3 || || 926.96 || Albiorix
|-id=S/2006_S_12 bgcolor=#fdf
|S/2006 S 12 || 4 || || 1035.06 || Albiorix
|-id=S/2007_S_8 bgcolor=#fdf
|S/2007 S 8 || 4 || || 836.90 || Albiorix
|-id=S/2005_S_7 bgcolor=#fdf
|S/2005 S 7 || 3 || || 939.75 || Albiorix
|-id=S/2007_S_11 bgcolor=#fdf
|S/2007 S 11 || 4 || || 859.53 || Albiorix
|-id=S/2019_S_29 bgcolor=#fdf
|S/2019 S 29 || 3 || || 853.62 || Albiorix
|-id=S/2019_S_31 bgcolor=#fdf
|S/2019 S 31 || 3 || || 882.24 || Albiorix
|-id=S/2019_S_34 bgcolor=#fdf
|S/2019 S 34 || 3 || || 935.45 || Albiorix
|-id=S/2020_S_15 bgcolor=#fdf
|S/2020 S 15 || 3 || || 807.82 || Albiorix
|-id=S/2023_S_17 bgcolor=#fdf
|S/2023 S 17 || 3 || || 855.94 || Albiorix
|-id=S/2023_S_18 bgcolor=#fdf
|S/2023 S 18 || 3 || || 855.65 || Albiorix
|-id=S/2023_S_54 bgcolor=#fdf
|S/2023 S 54 || 3 || || 863.35 || Albiorix
|-id=S/2023_S_55 bgcolor=#fdf
|S/2023 S 55 || 3 || || 818.51 || Albiorix
|}
See also
- List of natural satellites
References
</references>
External links
- David Jewitt pages
- Scott Sheppard pages
- Ephemeris from MPC
- Mean orbital parameters from JPL