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| Permanently shadowed regions | |
|---|---|
| Name | Permanently shadowed regions |
| Type | Surface feature |
| Discovered | Various missions and observations |
| Notable | Polar craters, permanently dark basins |
Permanently shadowed regions are surface areas on airless or near-airless Solar System bodies that receive negligible direct sunlight over long timescales. These regions occur where axial tilt, topography, and orbital dynamics produce enduring darkness, creating cold traps that influence surface chemistry and volatile retention. Studies by missions such as Lunar Reconnaissance Orbiter, MESSENGER, Dawn, and telescopes including Hubble Space Telescope and Arecibo Observatory have mapped and characterized many of these locales.
Permanently shadowed regions are defined by persistent absence of solar illumination due to local horizon geometry and planetary obliquity, described in analyses by NASA, European Space Agency, Roscosmos, Indian Space Research Organisation, and Japan Aerospace Exploration Agency. Characterization often references datasets from Clementine, Lunar Reconnaissance Orbiter, and ground-based radar from Goldstone Deep Space Communications Complex and Arecibo Observatory. The concept is central to mission planning for Artemis program, Lunar Gateway, BepiColombo, OSIRIS-REx, and Hayabusa2 follow-ups.
Permanent shadowing arises where axial tilt and local relief prevent sunlight incidence; explanations draw on work by Isaac Newton-era celestial mechanics extended in models by Pierre-Simon Laplace, Johannes Kepler, and modern orbital dynamics teams at Jet Propulsion Laboratory and European Southern Observatory. On bodies with near-zero obliquity like Mercury and the Moon, polar craters and steep rims produce enduring darkness, a phenomenon analyzed with thermal models from Lawrence Livermore National Laboratory and Johns Hopkins University Applied Physics Laboratory. Impact events attributed to families such as the Imbrium Basin and Caloris Basin create topography that seeds shadowed hollows, a process compared across studies involving Vesta and Ceres.
On the Moon, prominent examples include craters near Lunar South Pole such as Shoemaker (crater), Haworth (crater), Cabeus (crater), and areas mapped by Lunar Reconnaissance Orbiter Camera. Mercury hosts shadowed sites near the north pole of Mercury and south pole of Mercury within craters like Prokofiev (crater) and Enguré (crater), identified by MESSENGER. Dwarf planet Ceres presents permanently dark depressions in Occator Crater-adjacent terrain and polar hollows studied by Dawn, while asteroids such as Vesta show localized shadowing in basin interiors examined by Hubble Space Telescope. Icy moons including Europa, Ganymede, and Enceladus exhibit shadowed fissures and polar cliffs considered in mission concepts like Europa Clipper and JUICE.
These regions maintain extreme thermal environments with surface temperatures modeled by researchers at Caltech, MIT, and Brown University; lunar polar cold traps can reach below 40 K according to analyses leveraging radiometry from Diviner (instrument) and spectroscopy from Moon Mineralogy Mapper. Mercury’s shadowed craters register similarly low temperatures constrained by MESSENGER’s thermal infrared measurements and interpreted by teams at Southwest Research Institute. Low insolation leads to minimal diurnal variation, high surface coherence, and complex micro-shadowing influenced by regolith properties studied by Smithsonian Institution and Carnegie Institution for Science researchers.
Cold trapping enables accumulation of volatiles such as water ice, carbon dioxide, methane, ammonia, and organics; detection claims stem from work by Lunar Prospector, LCROSS, M3 (Moon Mineralogy Mapper), MESSENGER, and Dawn teams. Identification methods include neutron spectroscopy by Lunar Prospector, mass spectrometry by LCROSS, and radar backscatter studies by Arecibo Observatory and Goldstone Deep Space Communications Complex. Deposits have implications for in-situ resource utilization assessed by NASA, European Space Agency, and commercial partners like SpaceX and Blue Origin in planning for Artemis Base Camp and lunar surface operations.
Robotic and orbital investigations include Lunar Reconnaissance Orbiter, LCROSS, MESSENGER, and Dawn, while proposed and ongoing missions targeting shadowed polar terrain feature Artemis Program, VIPER (rover), BepiColombo, Lunar Flashlight, and mission concepts from Roscosmos and Indian Space Research Organisation. Observational techniques involve passive radiometry, active radar, neutron spectroscopy, and laser altimetry from instruments like Diviner (instrument), Mini-RF, LIDAR, and mass spectrometers developed by teams at Johns Hopkins University, NASA Goddard Space Flight Center, and European Space Agency laboratories.
Permanently shadowed regions are scientifically vital for understanding volatile delivery via comets, carbonaceous chondrite impacts, and solar-wind implantation studied in contexts involving D/H ratio measurements and isotopic investigations by Rosetta and sample-return missions such as Hayabusa2 and OSIRIS-REx. Practically, these cold traps are target reservoirs for propellant and life-support resources informing plans by NASA, ESA, JAXA, ISRO, and commercial entities including SpaceX for sustained exploration and habitation frameworks like Lunar Gateway and Artemis Base Camp. Their study intersects planetary protection policies from Committee on Space Research and strategic planning discussed at International Astronomical Union forums.