The exterior planet of the Solar system, nearest the earth, of one-half its diameter, with a mean distance from the sun of 141,000,000 m., round which it takes 686 days to revolve, in a somewhat centric orbit, and 24½ hours to revolve on its own axis, which inclines to its equator at an angle of 29°; examination of it shows that there is four times as much land as water in it; it is accompanied by two moons, an outer making a revolution round it in 30 hours 18 minutes, and an inner in 7 hours and 38 minutes; they are the smallest heavenly bodies known to science.