A wide, thin sheet of material that uses the pressure of light to propel a craft through space. Lightsails have been successfully demonstrated in Earth orbit using sunlight. Scientists and engineers are exploring the possibility of using lightsails to send craft to Mars and other worlds of the solar system. They also are evaluating laser-powered lightsails as a means to send tiny robotic probes to Alpha Centauri, the closest star system to our own. Although the initial thrust provided by a lightsail can be relatively small, the light pressure can be applied continuously for as long as needed, adding up to a substantial kick.