Geological Chronicle
Mare Frigoris, or the Sea of Cold, is an elongated lunar sea in the northern nearside of the Moon, spanning 1,446 kilometers across. Located along the northern outer margins of the Procellarum basin, the plain forms an east-west arc directly north of Mare Imbrium and the dark-floored crater Plato, extending east toward the northern boundary of Mare Serenitatis. At its western margin, the basalt plains merge into Sinus Roris (the Bay of Dew), creating one of the longest continuous stretches of volcanic lowlands on the Moon.
Unlike the dark titanium-rich basalts that cover southern maria such as Mare Tranquillitatis, the lava flows of Mare Frigoris are largely low-titanium basalts with a comparatively higher optical albedo. The geological history of the plain spans several lunar epochs. The surrounding basin bedrock dates to the Lower Imbrian epoch, while the eastern lava deposits erupted during the Upper Imbrian epoch. The western basalt flows cooled much later during the Eratosthenian epoch, recording long-lived episodic volcanism along the northern perimeter of the nearside.
Thermal contraction and tectonic stress within the cooling basalt sheets produced networks of wrinkle ridges across the floor of Mare Frigoris. These compressional ridges rise dozens of meters above the plains, tracing subsurface crustal faults and the edges of buried impact scars. Early telescopic cartographers applied several names to the formation: William Gilbert called it Insula Borealis around 1600, Michael van Langren designated it Mare Astronomicum in 1645, and Pierre Gassendi used Boreum Mare. The current name Mare Frigoris was established in 1651 by Italian astronomer Giovanni Riccioli.