Mare Frigoris

Mare Frigoris, meaning “Sea of Cold” in Latin, is a large basaltic plain situated in the far north of the Moon. It lies outside the principal ring structures of the Procellarum basin, immediately north of Mare Imbrium, and extends eastward toward the area north of Mare Serenitatis. The mare is also located north of the prominent crater Plato, a feature that makes it relatively easy to identify in lunar maps and telescopic views. Unlike a terrestrial sea, Mare Frigoris is not a body of liquid. It is a broad expanse of dark volcanic basalt that filled low-lying lunar terrain after ancient impacts and subsequent volcanic activity. Its surface records several geological periods. Material around the basin is associated with the Lower Imbrian epoch, while the eastern portion of the mare is linked to the Upper Imbrian epoch. Parts of the western region are assigned to the later Eratosthenian epoch. These differing ages indicate that the plain was not formed in a single event and that volcanic resurfacing occurred over an extended period of lunar history. The name belongs to the standardized system of lunar nomenclature developed by Giovanni Riccioli in 1651. Earlier lunar cartographers used different designations for the same general region. William Gilbert included it within a feature he called Insula Borealis, or “Northern Island,” on a map dating from around 1600. Michael van Langren identified the area as Mare Astronomicum, or “Sea of Astronomy,” on his 1645 lunar map, while Pierre Gassendi used the name Boreum Mare, meaning “Northern Sea.” Riccioli’s nomenclature ultimately became the established international naming framework for lunar surface features. Mare Frigoris has been relevant to both scientific exploration and popular representations of lunar activity. The region appeared prominently in “Behemoth,” the second episode of the 1973 BBC science-fiction miniseries Moonbase 3. It was also selected as the planned landing area for the fictionalized Apollo 15 mission depicted in the Apple TV+ series For All Mankind. In that fictional scenario, the crew diverts to Shackleton crater after learning that the lunar south pole contains a high concentration of water ice. The region has also figured in modern commercial lunar exploration. Japan-based private spaceflight company ispace attempted to land its second Hakuto-R mission at a site in the Mare Frigoris area in June 2025, but the landing attempt failed. Mare Frigoris therefore functions not as a commercial consumer brand or corporate enterprise, but as a recognized astronomical place-name used in lunar science, cartography, exploration planning, education, and fiction.

Mare Frigoris is a northern lunar mare formed through the accumulation of dark basaltic volcanic material in a broad, ancient lowland. It occupies terrain beyond the main inner rings of the Procellarum basin and is positioned north of Mare Imbrium. Its eastern extent reaches toward the region north of Mare Serenitatis, while the crater Plato lies immediately to its south. The feature's geography makes it an important reference point in descriptions of the Moon's northern hemisphere. The geological history represented by Mare Frigoris is composite rather than uniform. The material surrounding the mare is attributed to the Lower Imbrian epoch, an interval associated with the aftermath of major lunar impacts and the emplacement of extensive basin deposits. The eastern mare surface is assigned to the Upper Imbrian epoch, indicating a later phase of volcanic or resurfacing activity. The western material is associated with the Eratosthenian epoch, which followed the Imbrian period. These classifications show that different sections of the feature acquired their present surfaces at different times. Before modern standardized lunar nomenclature, European astronomers assigned several names to the northern plain. William Gilbert's map from approximately 1600 treated the area as part of Insula Borealis, or “Northern Island.” Michael van Langren's 1645 map used Mare Astronomicum, translated as “Sea of Astronomy.” Pierre Gassendi referred to it as Boreum Mare, or “Northern Sea.” Giovanni Riccioli's 1651 naming system replaced this variety of labels with Mare Frigoris, Latin for “Sea of Cold.” Riccioli's system was subsequently adopted and standardized in lunar cartography, making Mare Frigoris the enduring official designation. The area has attracted attention from lunar observers because of its extensive dark plain, its relationship to Plato and Mare Imbrium, and its position within the Moon's northern terrain. It has also appeared in cultural depictions of lunar settlement and exploration. The 1973 BBC science-fiction miniseries Moonbase 3 featured the region in its episode “Behemoth.” In the Apple TV+ alternate-history series For All Mankind, a fictional Apollo 15 mission initially plans to land at Mare Frigoris before diverting to Shackleton crater after the crew learns of significant water ice near the lunar south pole. Mare Frigoris entered the context of contemporary commercial lunar exploration when ispace selected a site in the region for the second Hakuto-R mission. The attempted landing in June 2025 failed. This event connected the long-established astronomical name with a modern private-sector lunar mission, although Mare Frigoris itself remains a physical lunar feature and not an operating organization, product line, or conventional commercial brand.

• 2025

  Hakuto-R 2 landing attempt

  [1]Mare Frigorisen.wikipedia.org

  ispace's second Hakuto-R mission attempted to land at a site in the Mare Frigoris area in June 2025, but the landing failed.

• 1973

  Mare Frigoris appears in Moonbase 3

  [1]Mare Frigorisen.wikipedia.org

  The lunar region featured prominently in “Behemoth,” the second episode of the BBC science-fiction miniseries Moonbase 3.

• 1651

  Riccioli establishes the Mare Frigoris name

  [1]Mare Frigorisen.wikipedia.org

  Giovanni Riccioli included Mare Frigoris, Latin for “Sea of Cold,” in the lunar nomenclature system that later became internationally standardized.

• 1645

  Michael van Langren uses Mare Astronomicum

  [1]Mare Frigorisen.wikipedia.org

  Michael van Langren's lunar map labeled the region Mare Astronomicum, meaning “Sea of Astronomy.”

• 1600

  William Gilbert maps the region as Insula Borealis

  [1]Mare Frigorisen.wikipedia.org

  On a lunar map dating from around 1600, William Gilbert included the area now called Mare Frigoris within Insula Borealis, or “Northern Island.”

A standardized astronomical place-name for a northern lunar mare and geological region, rather than a commercial brand.

1. 1Mare Frigorisen.wikipedia.org