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Moon View
Orbital Distance 2,323,500 km (from Mnemosyne)
Orbital Period 16.4 Earth Days
Keplerian Ratio N/A
Radius 5,663 km
Day Length 16.4 Earth Days
Atm. Pressure 0.58 atm
Surface Temp 31 °C
Surface Gravity 0.59 g
Mass 0.462 Earth Masses
Satellites N/A

Location: Milky Way / Hawking Eta / Thorne System / Mnemosyne

Prerequisite: Collector Ship (mission) (Mass Effect 2)


Lethe is the largest moon of Mnemosyne, massive enough to retain its own thin atmosphere of methane and nitrogen, and heated by the brown dwarf to relatively moderate temperatures. While nearly the size of Earth, its overall density is low, suggesting a paucity of valuable heavy metals. It is tidally locked to Mnemosyne, one hemisphere always bathed in the brown dwarf's heat and dim red light.

The moon experiences constant weak tectonic activity, driven by the tidal fluxes of Mnemosyne's gravity rather than Lethe's own internal heat. Several large, ancient volcanoes release wide-ranging flows of molten silicate.

Mineral DepositsEdit

Initial Scanner Result: Rich

Mineral Amount Approximate Value
Palladium High 16,600
Platinum Medium 9,000
Iridium Low 4,700
Element Zero None 0


  • Lethe may be named after a river in Hades in Greek mythology.
  • Lethe (λήθη) is an Ancient Greek noun meaning "forgetfulness." The moon orbits Mnemosyne (μνημοσύνη), which shares its name with an Ancient Greek noun meaning "memory."

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