Brian McFalls, age 11, of Hanna, Alberta, for his question:

How many solar systems are there in the Universe?

Astronomers say that our sun and its planets formed ages ago from a hazy cloud of cosmic gases. They now have some new evidence on this subject. It suggests that all of the starry suns in the universe may have formed in the very same way. If so, we can expect many of them to be solar systems, somewhat like our own sun with its family of orbiting planets. There are about 100 billion stars in our Galaxy and perhaps 100 billion other galaxies in the universe. Most of these starry suns may be orbited by planets.

We cannot, of course, prove this theory. But astronomers have a lot of indirect evidence to suggest that it is true. What's more, they have some direct evidence to prove that ours is not the only solar system in the universe. A big planet has been found orbiting around another star and several others seem to have planets. With more work and better instruments, no doubt we shall find them. Meantime, there seems to be no shortage of solar systems in the universe.