Research the distances of the planets from the sun, and
develop a scale to represent them. For example, if a scale
of 1 inch = 1,000,000 feet is used, the size of the sun can
be represented by a quarter, and Jupiter (the largest planet) by a pinhead. The other planets would then be almost too small to be seen.

Using coins is quite limiting. It seems to me that you should cut circles out of cardboard to make images of the planets. Cut a 2 ft, 7 1/8 inch diameter circle from red or orange construction paper to represent the sun. Using that same scale, you cut lesser sizes for all the planets, with the smallest circle maybe 1 inch in diameter.

On a playground, the sun's circle and Jupiter's circle can be placed 483 inches (40 feet 3 inches) apart. Markers can be placed for the other planets to indicate their mean distances from the sun.

What is a "mean distance?" Is it cruel? Unkind? What is
it? Better whip out your dictionaries and find that definition!