The NASA Planetary Fact Sheet lists each planet's diameter, day length, year length, surface gravity, temperature, moons and rings. Read as a table, the numbers sort the planets into two families. The four inner planets are small, rocky worlds with solid surfaces. The four outer planets are giants with no solid surface, made mostly of gases and ices. Earth-based telescopes, space telescopes and spacecraft each add different data to the table. This week the crew cuts paper circles to scale and discovers how small Earth really is.