Unknown Vex chassis
From Destinypedia, the Destiny wiki
The Unknown Vex chassis is a type of Vex chassis that is found in various areas but mainly in the Aphix Conduit, Io, Nessus, and Mercury as well. It is unknown what they do or what their function is but with them being mainly found around various Vex structures suggests possible monitoring of the Vex Network.
They look like small black and white cubes that float around in various majority Vex areas. They are very small but can make themselves larger by expanding parts of their shell, much like a Ghost. The Unknown Vex chassis seems to be programmed to go in a set area or path, most likely for monitoring.