Arvon subtends an angle of 13 42 arc minutes Having a diameter larger than Krelln, total eclipses of Krelln occur every 547 2 days. The physical characteristics of Arvon differ from those of Krelln A density value of only 2.02 g/cm3 results from the presence of large amounts of subterranean water ice and frozen carbon dioxide Cratenng is evident, but is less pronounced due to the more fluid crustal structure Arvon has no measurable magnetic field and is geologically inert No evidence of tectonic activity has been detected by Arrakian scientists Extaris The fourth planet, Extans, is the smallest of the outer planetary bodies with an equatorial radius of 8,112 km Extans has a mean density of only 1 31 g/cm3, such a low density is characteristic of the outer planets. The primary constituents of Extaris's atmosphere and their relative abundance are atomic helium 0.83, Zeon 0 15, carbon monoxide 0 01, and trace amounts of Zenon, Krypton, and cyanogen Atmospheric pressures exceed 250 stan- ARRAKIS, ASTRONOMY 22 ARRAKIS, ASTRONOMY dard atmospheres, yet Extaris's weather is essentially benign. This is due to three factors; one, the orbit is nearly circular (eccentricity 0.015); two, the axial rotation is slow, with the Exlaris day equal to 42 hours; and three, the upper atmospheric layer of Zeon ice refects 97% of the incident radiation from Canopus back into space. These effects minimize the transfer of thermal energy to the lower atmosphere. The resulting lack of thermal gradients prevent the formation of significant cyclonic or amicyclonic circulation. > Unlike the inner high-density- planets. Extaris and the other outer planets have several satellites. Extaris has five satellites that orbit die primary at distances from 117,000 km to 399,000 km. The four inner, icy satellites are in circular orbits and were probably formed from the same molecular accretion as Extaris. The rocky outer satellite, however, occupies an extremely elliptical orbit (eccentricity 0.55) which is inclined to the equatorial plane by 19. Furthermore, this satellite, Aja by name, orbits Extaris in a retrograde manner. These . orbital characteristics clearly imply that Aja was gravitationally captured eons ago. No record of first observations of Aja has been found. The four inner satellites are composed of a thick ice mantel surrounding an outer core of silicate material. At the center of the outer core is a very small, dense, inner core of nicfcel-iroa. This inner core has no fluidity which accounts for the lack of measurable magnetic fields generated by internal dynamo activity. Vfen.Ven, the firth planet, is the giant of the Canopus planetary system with an equatorial radius of 210,500 km. Together, Yen and CanopiiK account for 99.9% of the total mass and angular momentum of the system. The planet orbits in a mildly elliptical orbit (eccentricity 0.11) at a mean distance of 2.58 x 10* Km. The planet kjust under the mass limit that separates planet from star.