Science Questions

How fast do you have to go to leave the solar system?

One of the voyager probes has left the solar system. What speed (and relative to what?) did it have to achieve in order to do so? Could anything escape the solar system directly from the Earth using existing technology? Mike Roberts (via email)

There’s no special technology involved, it’s basically the same as when you launch a rocket off the surface of the Earth; you have to go fast enough to escape the Earth’s gravity.  If you were standing on the surface of the sun (and could cope with the 5000 degree temperature) and launched a rocket, you would have to get it up to 617.5 kilometres per second (km/s) to get it to escape the gravitational attraction of the sun and out of the solar system.

As the Earth is already travelling at 30 km/s you don’t need to get it quite as fast, but you couldn’t possibly launch something at those sorts of speeds.  To get out to the far reaches of the solar system, and beyond, you need to get a boost by whizzing past another planet.  This is called ‘gravity assisted’ because you use the gravity of a planet to sling shot you further out into the solar system.

June 2007