New Delhi, March 8 -- Some things in our lives are givens. We grow up with them firmly embedded in our brains and consciousness, not questioned to any degree. The shapes of our continents is one of those. The way night follows day follows night, without end, another. Green leaves on trees, screws that are tightened clockwise, the miaow of a cat: still more.

One more in that vein? Our solar system had nine planets, with even this excellent mnemonic to remind us of their names: My Very Educated Mother Just Showed Us Nine Planets. All in orbits around the Sun, that's Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.

Yes, Pluto. Remember that one? We of a certain vintage were taught that our solar system's ninth and o...