The missions also provided data that substantially reformed and reconfigured these ideas ; for instance , now it is understood that the surface of Halley is largely composed of dusty , non-volatile materials , and that only a small portion of it is icy .
The missions also adjusted these ideas . For example , it is now known that the `` surface '' of Halley is largely composed of dusty , non-volatile materials , and that only a small portion of it is icy .