Entrances To Underground Alien Bases On Planet Mercury Found! Jan 9, 2018, UFO Sighting News.

Date of discovery: Jan 9, 2018
Location of discovery: Mercury, Mariner 10 mission
Source photo: http://ser.sese.asu.edu/M10/IMAGE_ARCHIVE/CLEAN/0529044.png

Here are some fake craters on planet Mercury. The center of the crater actually goes up instead of down, like a dome, but the top part of the dome is open (black) so that ships can come and go into the underground bases. In space, its best to build underground to conserve heat, and increase safety from meteorites and other anomalies. 
Scott C. Waring