A magnetosphere is the region around a planet where its own magnetic field, rather than the solar wind, controls the motion of charged particles. Earth's deflects most of the incoming solar particles, shielding the atmosphere from erosion and funnelling some toward the poles to create aurorae. Jupiter's is the largest structure in the solar system, so vast that if it glowed visibly it would appear several times the width of the full Moon. Planets without one, such as Mars, have lost much of their atmosphere to space over billions of years.