I remember the first time the concept of another world entered my mind. It was during a walk with my father in our garden in Sri Lanka. He pointed to the Moon and told me that people had walked on it. I was astonished: Suddenly that bright light became a place that one could visit.

Schoolchildren may feel a similar sense of wonder when they see pictures of a Martian landscape or Saturn’s rings. And soon their views of alien worlds may not be confined to the planets in our own solar system.

After millenniums of musings and a century of failed attempts, astronomers first detected an exoplanet, a planet orbiting a normal star other than the Sun, in 1995. Now they are finding hundreds of such worlds each year. Last month, NASA announced that 1,235 new possible planets had been observed by Kepler, a telescope on a space satellite. Six of the planets that Kepler found circle one star, and the orbits of five of them would fit within that of Mercury, the closest planet to our Sun.

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