Natrun and Rum Paterae

Lore & Background

Natrun and Rum Paterae are located on the hemisphere of Ganymede that never faces Jupiter, due to the moon's synchronous rotation. An observer at either patera would never see Jupiter in the sky. The depressions are situated between two bright grooved-terrain regions, Sippar Sulcus and Mummu Sulcus, with the crater Bes to the north and the bright ray crater Osiris to the east. To the southwest lies another potential cryovolcanic caldera, Musa Patera.

In accordance with IAU naming conventions, all paterae on Ganymede are named after wadis—desert river valleys in the Middle East. Natrun Patera is named after Wadi El Natrun in Egypt, which hosts several historically important monasteries and is near the site where Antoine de Saint-Exupéry's plane crashed. Rum Patera is named after Wadi Rum in southern Jordan, famous for its prehistoric petroglyphs and active archaeological site. Both names were approved by the IAU in March 2015.

Preliminary analyses suggest these paterae may be ground-level cryovolcanic calderas, with open rims and scalloped-like lobate shapes indicating slushy water ice once flowed across the area. However, as of 2026, the cryovolcanic origin remains uncertain; alternative processes such as mass wasting and fracturing may also have shaped them.

Reader's Guide

Natrun and Rum Paterae hold significance as potential evidence of cryovolcanism on Ganymede, a process that would involve slushy water ice rather than molten lava. Their scalloped shapes and irregular margins suggest past flows, but the origin remains uncertain as of 2026. Higher-resolution imaging and detailed spectroscopic observations are needed to determine conclusively whether these features are cryovolcanic.

Voyager 2 first imaged the paterae in July 1979, but their small size and the spacecraft's distance prevented clear resolution. The Galileo probe provided the first high-quality images in May 1997, resolving details as small as 180 meters per pixel. The European Space Agency's Juice spacecraft, en route to Jupiter and scheduled to arrive in July 2031, is expected to enter low orbit around Ganymede in 2034. Natrun and Rum Paterae are considered high-priority targets for Juice, as high-resolution imaging may help resolve the long-standing question of whether cryovolcanoes exist on Ganymede.

Did You Know?

• Both paterae are named after wadis in the Middle East: Wadi El Natrun in Egypt and Wadi Rum in Jordan.
• The Galileo probe imaged the paterae at a resolution of 180 meters per pixel during its G8 flyby in May 1997.
• As of 2026, the cryovolcanic origin of these paterae remains uncertain, with alternative processes like mass wasting and fracturing also possible.