According to a report by Space.com, the rover's surprise discovery was made during exploration activities on lunar day 8, which began on July 25. Each lunar day lasts for two Earth weeks and during this time the solar-powered rover carries out scientific observations, measures radiation and surveys its surroundings. Three days into day 8, a member of the Chang'e 4 team was reviewing images taken during by the rover and noticed a strangely colored material, distinct from the gray soil around it. So, the team instead turned its attention toward the substance and sent the rover towards the crater for a better look. The Yutu-2 "drive diary" says the team commanded the rover to point its spectrometer, a device which can evaluate the composition of materials, towards the unusual substance.
The team didn't indicate what the substance might be and they haven't shared an image of the weird material. The team did, however, share an image of the rover heading for the crater to have a gander at what's inside.
I know you're thinking aliens but Andrew Jones, a journalist reporting on the Chinese space program, wrote that one possible explanation is that the gel-like substance is melted glass, created after a meteor strike.
