From Destinypedia, the Destiny wiki
The Mercurian Pyramid is the name used to a massive alien vessel holding position above the Fields of Glass on Mercury. Like its counterpart on Luna, this vessel is a part of the aforementioned fleet that attacked the Sol System during the Collapse, and are fragments of the Darkness.
Overview and Layout
Like its brethren, the outside of the Pyramid's hull is covered in segmented panels that vary in pattern, with some having vertical lines and other with patterns resembling circuitry. Much like the Traveler, the surfaces of the Pyramid seem to be composed of some form of rock-like material, occasionally having an uneven or chiseled appearance, giving the ship an almost handcrafted quality. In contrast to its Moon counterpart, the Mercurian Pyramid is rougher in appearance, suggesting more wear and tear to its hull.
It is unknown if there is a habitable interior within.
Season of Arrivals
Weeks following the Io Pyramid's arrival, the Mercurian Pyramid arrived with 2 others on its aforementioned planet. Following its arrival, it hovered ominously above the Caloris Basin, blotting out the sun with its massive appearance, before beginning to terraform the planet.