Fourier (crater)

Fourier (crater)
Name	Fourier
Caption	Oblique Lunar Orbiter image of Fourier
Diameter	51 km
Depth	1.7 km
Colong	279
Eponym	Jean-Baptiste Joseph Fourier

Fourier (crater) is a lunar impact crater located near the northeastern limb of the visible side of the Moon. The feature is a worn and intruded formation with a shallow floor and irregular rim that has been modified by subsequent impacts and volcanic resurfacing. The crater has been imaged by multiple lunar missions and mapped in studies by planetary scientists interested in lunar stratigraphy, mare volcanism, and impact processes.

Description

Fourier is a degraded impact structure with a diameter of approximately 51 kilometres and a modest depth near 1.7 kilometres. The rim is breached and irregular, showing evidence of rim erosion, rim–floor slumping, and superposed small craters. The interior contains a levelized floor and a low central uplift that is largely buried or subdued. The crater's degraded morphology links it to other worn lunar craters studied in surveys by the Lunar Reconnaissance Orbiter, Clementine (spacecraft), Apollo 15 photographic campaigns, and the earlier Lunar Orbiter program.

Location and Surroundings

Fourier lies near the northeast limb of the lunar nearside, positioned east of the prominent Mare Frigoris and northwest of the Lacus Mortis region. It is situated southwest of the larger crater Boscovich and northeast of the flooded crater Byrgius A; nearby named features include the rim of Grove (crater) to the west and the craterlets associated with the Rimae Sirsalis system to the south. Because of its limb-proximal location, libration effects influence its visibility from Earth, making it easier to study during favorable libration as exploited by observers at the Royal Observatory, Greenwich, the United States Geological Survey, and amateur groups using facilities like the International Occultation Timing Association.

Morphology and Geology

The rim of Fourier exhibits uneven heights and incisions produced by subsequent impacts, producing a scalloped circumference similar to other eroded craters catalogued in morphological classifications used by the International Astronomical Union and researchers at the Smithsonian Astrophysical Observatory. The crater interior shows mare-like resurfacing in places, with basaltic infill interpreted in comparative studies with basalts sampled by Apollo 11, Apollo 12, and inferred from spectral data from the Moon Mineralogy Mapper aboard Chandrayaan-1. Ejecta from nearby impacts and secondary crater chains overlay portions of Fourier's rim and floor, indicating complex cross-cutting relationships used in stratigraphic mapping by teams at the Jet Propulsion Laboratory and the Lunar and Planetary Institute.

The floor hosts low-relief wrinkle ridges and subdued central topography consistent with isostatic adjustment and lava ponding documented in studies of plains-forming events near Oceanus Procellarum and Mare Imbrium. Reflectance measurements from the Clementine (spacecraft) UVVIS experiment and the Kaguya (SELENE) spectrometer suggest a mix of highland anorthositic materials and mare basalts on and around Fourier, echoing compositional contrasts seen at sites like Copernicus (crater) rim exposures and the ejecta blankets of Tycho.

Age and Formation

Crater counting and stratigraphic analyses place Fourier among middle-aged to ancient lunar features, with formation likely in the Nectarian to early Imbrian periods based on superposition relationships and degradation state. Its subdued rim and partially filled floor imply significant post-impact modification from mare volcanism and impact gardening during the Imbrian and Eratosthenian epochs. Comparative chronology uses calibration from radiometric ages of returned samples from Apollo missions and crater size-frequency distributions refined by teams at the Planetary Science Institute and the United States Geological Survey.

Observations and Imaging

Fourier has been photographed and analyzed across numerous missions: oblique and high-resolution imagery from Lunar Orbiter frames, multispectral mapping by Clementine (spacecraft), topographic profiles from the Lunar Reconnaissance Orbiter's Lunar Orbiter Laser Altimeter, and spectral datasets from Chandrayaan-1 and Kaguya (SELENE). Ground-based telescopic observations from observatories such as the Mount Wilson Observatory and the Mauna Kea Observatories have supplemented spaceborne data, particularly during favorable librations. Historical atlases like those from the United States Geological Survey and the Collins Atlas of the Moon include cartographic depictions of Fourier used by selenographers and amateur lunar observers affiliated with organizations such as the British Astronomical Association.

Nomenclature and History of Study

The crater name commemorates the French mathematician and physicist Jean-Baptiste Joseph Fourier, whose contributions to heat conduction and harmonic analysis influenced scientific disciplines recognized by the International Astronomical Union. The designation was adopted in mid-20th-century lunar nomenclature compilations compiled by the IAU Working Group for Planetary System Nomenclature and earlier catalogues produced by E. E. Barnard-era selenographers and cartographers at institutions including the Royal Astronomical Society and the United States Naval Observatory. Scholarly attention to Fourier increased with photographic coverage from the Lunar Orbiter missions and photogeologic mapping projects led by researchers at the Lunar and Planetary Institute and the Smithsonian Institution, forming the basis for modern geological interpretations.

Category:Lunar craters