Mercury is the smallest planet in our solar system and the closest planet to the sun. It is dry, very hot and has no moons or atmosphere. Mercury's surface is similar to that of our moon -- dark grey, rocky and covered with deep craters, mountains, valleys and plains. Craters at both poles contain water ice. Unlike our moon, Mercury's surface is covered with small ridges, called wrinkle ridges, that were created soon after the planet was formed. The craters and rocks were created by asteroids that bombarded the planet over billions of years. With homemade play dough and a few household items, you can recreate in minutes what took nature aeons to accomplish.
Mix flour, salt, water, oil and the cream of tartar in a saucepan. Add several drops of various food colours until the dough turns dark grey. Cook briefly over a low heat just until the dough forms a ball. Cool slightly before handling.
Cover the polystyrene ball with dough. Create a wrinkled surface by pushing the dough sideways gently with the edge of a butter knife to make small ridges about 3 mm (1/8 inch) high. Repeat until the entire surface is covered with wrinkles.
Use your fingertips, a pencil eraser and other objects to make different-sized dents and craters in the dough. Make indentations with a ping pong ball or golf ball to make the polar craters.
Create a rocky surface by embedding pieces of gravel irregularly in the dough, leaving some areas smooth.
Straighten one end of the paperclip and stick it into the ball to create a hook to hang the model from a piece of string. Allow the dough to dry completely.
Paint the centres of the polar craters white to represent ice.
Use latex gloves when moulding the homemade dough around the ball so the food colouring doesn't stain your hands.
Store leftover dough in an airtight plastic bag or container.
Use real modelling clay that has turned grey with repeated mixing of colours instead of making your own.