The Big Question: Sizing up the asteroids

How do spacecraft like Voyager 2, the only spacecraft to visit Neptune and Uranus and - as at January 2001 - 9.4 billion km from the sun, get past the asteroid belt and how long would it take to get to our planetary neighbours travelling at the approximate speed of a commercial jet airliner, i.e. 1000km/h?

The asteroid belts are not nearly as crowded as they look in diagrams or movies. The total amount of material in the asteroids is estimated to be about one thousandth as much as in the Earth, but it is spread in a band more than 200 million km wide. So a spacecraft would be quite unlucky to hit an asteroid on the way through.

The distance to the other planets varies greatly depending on where they are in their orbits relative to Earth, so let's assume they are all in a straight line and so as close as possible.

Flight time at 1000 km/h:

Mercury - 10 years, 23 weeks, 6 days.

Venus - 4 years, 37 weeks, 4 days.

Mars - 8 years, 48 weeks, 3 days.

Jupiter - 71 years, 37 weeks, 3 days.

Saturn - 145 years, 37 weeks, 3 days.

Uranus - 310 years, 15 weeks.

Neptune - 495 years, 46 weeks, 3 days.

Pluto - 655 years, 51 weeks, 3 days.

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