Eshmun (crater)

Lore & Background

Eshmun is named after the tutelary god of the Phoenician city of Sidon, who was the god of healing. An inscription on an ancient sarcophagus of a Sidonian king likely states that Eshmun is the 'Baal of Sidon,' where Baal means 'lord.' The name follows the IAU's convention of naming craters on Ganymede after deities, heroes and places from Ancient Middle Eastern mythologies, and was approved in 1979.

The crater features a central dome surrounded by a circular trench, with an outer rim approximately 98 kilometres in diameter. Dome craters like Eshmun are fairly common on Ganymede and other icy moons. Planetary scientists believe they form when meltwater develops beneath impact craters after an asteroid or comet strikes the moon's surface. As the subsurface meltwater refreezes and expands, it fractures and uplifts the crater floor, eventually producing the distinctive dome. Domes usually only form if a crater is more than 60 kilometers in diameter.

Eshmun is located at the southwestern boundary of a bright, grooved terrain called Sippar Sulcus. To its northeast lies the similar dome crater Melkart, and to its east are the craters Erichthonius and Amset, as well as the junction between Sippar Sulcus and Erech Sulcus. To the southeast is the crater Bes. Because Ganymede rotates synchronously, Eshmun is on the hemisphere that always faces away from Jupiter, so an observer there would never see Jupiter in the sky.

Reader's Guide

Eshmun is significant as a well-studied example of a dome crater on Ganymede, a type of impact feature that does not occur on rocky worlds like Earth or the Moon. Its structure—a central dome surrounded by a circular trench—provides insight into the unique geological processes on icy moons, particularly the role of subsurface meltwater and its expansion upon freezing. The crater's formation model, involving meltwater development beneath the impact site and subsequent uplift, helps planetary scientists understand how impacts affect icy surfaces differently than rocky ones.

Eshmun was first imaged by Voyager 2 in July 1979 at a resolution of about 500 metres per pixel, which revealed details of its central dome and scarps. The Galileo probe observed it during its flyby of Ganymede in June 1996, though it did not image Eshmun at the same high resolution as the nearby dome crater Melkart. The European Space Agency's Jupiter Icy Moons Explorer (Juice) orbiter, scheduled to arrive at Jupiter in July 2031, is expected to image Eshmun at a higher resolution than Voyager 2 achieved. The crater's location on the far side of Ganymede from Jupiter adds to its interest, as it lies in a region that was not visible to early Earth-based observations.