China's Chang'e 4 lander and Yutu 2 rover entered sleep mode for the approximately 14-day lunar night, during which time radioisotope heater units kept them warm through temperatures as low as minus 190 Celsius (minus 310 Fahrenheit). Waking up on February 6, Yutu 2 soon came across an unusual rock that stuck out from the surrounding Lunar landscape.
The rock – which the Yutu 2 team decided to refer to as a "milestone" rather than the much more dramatic "monolith" we'd all been hoping for – was jutting out of the ground, capturing the China National Space Administration (CNSA)'s curiosity and warranting a closer approach.
The next day they took a closer look, giving clues to what might have formed the odd "stalagmite" on the Moon.
The shard-like shape suggests that the rock is young, geologically speaking, given that it hasn't been worn down and rounded, just like you would find rounded stones on a beach.
"It seems to have a shard-like shape and is sticking out of the ground. That's definitely unusual," NASA Postdoctoral Program Fellow at the Goddard Space Flight Center Dan Moriarty told Space.com.
"Repeated impacts, stresses from thermal cycling, and other forms of weathering on the lunar surface would all tend to break down rocks into more-or-less 'spherical' shapes, given enough time."
He suggests that the rock was likely ejected from an impact, likely from a nearby crater.
The team plan to use the rover's Visible and Near-infrared Imaging Spectrometer equipment to analyze the rock further. The tool detects light that is scattered off the rock, in order to analyze its makeup.
The tool was used to analyze the "gel-like" substance that was found on the surface of the Moon in 2019. The substance turned out to be similar to samples taken by the Apollo 17 mission in 1972, which was also described as “dark, broken fragments of minerals cemented together and black, shiny glass”. Analysis revealed that it was likely rock that had been melted together during an impact event.