The Sea of Frigoris (‘Sea of Cold”) aptly named for the most northern lunar sea which runs along the top of Mare Imbrium.

Clockwise from lower left, the Montes Teneriffe rise out of Mare Imbrium, with spectacular Mons Pico a solitary peak rising 2 km high above the mare floor. The basalt-covered floor of the 101-km-wide Plato crater lies just north, with a massive block some 25 km long (southeast of Bliss) slumping off the western crater wall and casting heavy shadow onto the crater floor. Rimae Plato winds eastward from the flank of Plato for some 87km.

To the east (right), an arcuate series of craters from south to north are Protagoras, Archytas, Timaeus, Epigenes and Anaxagoras. There are even older, pre-Nectarian age (>3.92 billion years) impact craters that remain as eroded depressions (W.Bond, Goldschmidt, Mouchez and Birmingham). Philolaus lies further north on top edge of the image. Fontenelle lies on the northern shoreline of Mare Frigoris.

A 600 km length of Mare Frigoris is imaged here. A series of dorsa (“wrinkle ridges”) are prominent and run across the floor of Mare Frigoris from Fontenelle southeast to Protagoras. These ridges (which can reach up to 300m elevation) are evidence of tectonism related to thermal shrinking of the mare over geological time.

The lunar north pole is not far north, with Anaxagoras lying about one degree south of the moons theoretical ‘arctic’ area. Consequently, the north-facing inner slope of Anaxagoras’s crater wall (and other deeper polar craters) remains in perpetual darkness, never seeing the lunar sunrise. For this reason, the Lunar Prospector probe and Clementine were tasked with looking at the potential cold traps at the bottom of these polar craters for evidence of perpetually frozen (cometary) H2O embedded in the regolith that has escaped sublimation over the aeons. Results from the Lunar Prospector probe and the Clementine mission were encouraging, with strong hydrogen signal in many of the permanently shaded polar craters - where temperatures reach as low as 38 Kelvin above absolute zero (minus 235 Celcius). At <110 Kelvin (minus 163 Celcius) the timeframe to sublimate lunar ice (evaporate solid to gas) is around a gigayear (a billion years) making sub-surface water ice a viable explanation for the high hydrogen counts. However research is ongoing to determine if the hydrogen signal is from water ice or from hydrogen delivered to the poles by the solar wind.