Mike Roberts (via email) asked:
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?
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.