How violent was that planet crash? Astronomers check the dust.

Around some young stars, primitive planets smash into each other so hard they vaporize rock, leaving behind clouds of glassy bits in space.Softer glancing blows grind rock into something finer, like the green sand on some Hawaiian beaches. Astronomers found both types of crash debris while studying a sample of 21 young star systems.Each of these stars carries an unusually heavy load of warm dust in the same zone where Earth and the other rocky planets — Mercury, Venus, and Mars — orb