Amset (crater)

Lore & Background

Amset is a typical impact crater on Ganymede's icy surface, with a diameter of only about 11 kilometres. It is superimposed on both the older, rugged terrain of Marius Regio and the younger, grooved terrain of Erech Sulcus, strongly suggesting it is younger than both. The crater features a central peak, which on Ganymede forms when meltwater from the impact accumulates beneath the crater floor, refreezes, and expands, cracking and ballooning the center upward—a process distinct from central peak formation on rocky bodies like Earth's Moon.

The crater is named after Imsety (alternative transliteration Amset), an ancient Egyptian god who protects the liver of a deceased person's mummy and is one of the four Sons of Horus. The name follows the IAU convention of naming Ganymede craters after deities, heroes, and places from Ancient Near Eastern mythologies, and was approved in 1997.

Amset lies within the Uruk Sulcus quadrangle (Jg8) on the hemisphere of Ganymede that never faces Jupiter, meaning an observer at the crater would never see Jupiter in the sky. It is located near the junction of Erech Sulcus and Sippar Sulcus, to the west of Erech Sulcus, with the crater Erichthonius to its east, Eshmun to its southwest, and the major ray crater Melkart to its east.

Reader's Guide

Amset's significance lies in its status as a recent crater that overlies both ancient and younger terrains, providing a clear stratigraphic marker for dating surface features on Ganymede. Its small size (11 km) makes it difficult to observe, yet it was fortuitously imaged in detail by the Galileo spacecraft during a close flyby in May 1997, allowing scientists to study its morphology. The crater's central peak is a key example of how impact processes differ on icy bodies compared to rocky ones: on Ganymede, central peaks form through meltwater accumulation and refreezing, rather than through crustal rebound as on Earth's Moon. This distinction helps planetary scientists understand the thermal and mechanical properties of Ganymede's icy crust. Amset's location on the Jupiter-facing hemisphere that never sees Jupiter adds to its unique geographic context. Future observations by the Juice orbiter, scheduled to arrive at Jupiter in July 2031 and later enter low polar orbit around Ganymede, could potentially image Amset at a resolution never achieved before, furthering knowledge of small crater formation and evolution on icy moons.

Did You Know?

• Amset is only about 11 kilometres (6.8 mi) in diameter.
• Its central peak formed when meltwater refroze and expanded, cracking the crater floor upward.
• The crater was first imaged by Voyager 2 in July 1979 as a 12x12-pixel feature.