Another alternative to blasting toward distant planets using rocket thrusters is to sail there. But what good are sails in an environment that doesn't have wind? Enter the solar sail!
Solar sails use the sun as an engine. The sun emits photons -- the basic units of light. We know that photons act as both waves and particles. Photons can seem insubstantial to us here on Earth but they exert a force on objects as they come into contact with them. This includes solar sails.
A solar sail is made of an ultrathin mirror that stretches across a large area. As photons strike the mirror, they exert a force and push against the sail. The sail is hit by billions of photons -- enough to push the sail and anything it might be tugging along through space.
At first, traveling in a vehicle pulled by a solar sail would be pretty dull. You wouldn't have a great deal of initial thrust like you do with a rocket. But the power of those photons can't be denied, and your spacecraft would continue to accelerate well beyond the point a thruster could manage. Not only do you not have to worry about fueling your spacecraft for interplanetary travel, you'll also reach your destination faster!
Solar sails could work well in space, but they aren't designed to get a craft off a planet's surface. For that, we'd still have to either use rockets or construct the spacecraft while in orbit. And a solar sail might be able to get us to another planet but without other means of leaving our new world we'd be stuck there. But for a one-way trip to another planet, a solar sail could be just the thing -- and you never need to worry about running out of fuel.