Sunday, January 16, 2005

Getting there

Almost every school room has a solar system poster with the planets lined up like soldiers on parade, or a dangling mobile with the planets jostling each other in the breeze. These illustrations do little to convey the true scale of the solar system -- or the achievement of Cassini-Huygens.

Imagine the Sun -- our blazing star, nearly a million miles in diameter -- as a smallish grapefruit on the goal line of a football field. Earth is a salt grain on the 10 yard line, and Saturn a pea at the far end of the field. Now, in your mind's eye, delete the ground, the bleachers, the goal posts, and everything else except the grapefruit, the salt grain and the pea. Set the salt grain and the pea in motion.

Now imagine that scientists and engineers on the salt-grain Earth decide to send a spacecraft to pea-sized Saturn, a football field's length away. The journey will take seven years, and make several loop-the-loops around the Sun, picking up gravitational kicks from the inner planets. The craft swings by pea-sized Jupiter out there the 50-yard line, getting another bit of ummph. Then it's on to Saturn.

And not just finding the planet, but dropping a package of instruments -- touchdown! -- onto its dustspeck moon.