Attempt to do a more or less scientifically correct solar system. Planet sizes and colors approximated from astronomical data. Still, it is not 100 percent realistic ;-)

All spheres are worked in single crochet (sc).
Once you come to the last couple of rows, start stuffing.
After the last decrease row, fasten off, cut yarn to about 20cm. Using a wool needle, sew into each stitch, pulling tight so that the hole closes. Weave in ends.

Planet Rows Colors used

Mercury 16 grey multicolor
Venus 16 beige multicolor
Earth 30 dark blue, green, ice blue
Mars 20 rust
Jupiter 40 brown multicolor
Saturn 20 beige multicolor + sand (for rings)
Uranus 26 blue multicolor
Neptune 20 dark blue + ice blue (for rings)
Pluto 10 silver grey

Abbreviations:
sc = single crochet
6 = work 6 sc
ch = chain
inc = 2 sc in same stitch
dec = single crochet decrease, preferably invisible
6 dec = decrease 6 times in row
even = single crochet in each stitch around
… = repeat until end of the row
(60) = row should have 60 stitches in the end