Bernard Lettington, age 10, of Des Moines, Iowa, for his question:

WHICH PLANET WAS FORMED FIRST?

There are nine planets in the sun's family, and all of them belong to the same litter. They formed perhaps five billion years ago. Naturally, there was nobody around to take notes. But astronomers have a theory to explain how it all happened. It began when a stupendous cloud of dusty gases began to shrink. As it grew smaller, its scattered fragments crowded closer. In time they clogged together to form a huge ball of gases, surrounded by nine small chunks.

The ball of gases, of course, became the sun. The nine little chunks became the solid planets. They orbited the sun, each at its proper distance. Then at last the sun's blazing furnace was set on fire  and the whole solar system was bathed in its light. Since all the planets were formed at the same time, they are all the same age.