Isis (Ganymede crater)
Bright pit crater on Ganymede, named for Egyptian goddess Isis.
Isis is a large, bright pit crater on Ganymede, Jupiter’s biggest moon. It sits a bit more than two-thirds of the way from the moon’s equator down toward its south pole.
**Naming** The crater takes its name from the Egyptian goddess Isis, who rose to become Egypt’s most powerful mother goddess. She governed magic, healing, protection, fertility, motherhood, and childbirth, and played many roles in Egyptian myth. Isis was the wife of Osiris; after Set killed and dismembered him, she pieced him back together. She and Osiris had a son, Horus, who later avenged his father’s death. The International Astronomical Union (IAU) rules that craters and geological features on Ganymede must be named after deities, heroes, or places from ancient Near Eastern mythologies, which includes Egyptian myths. Nearby craters like Osiris and Anubis follow the same Egyptian theme. The name was approved by the IAU in 1979.
**Location** To Isis’s west lies a bright ray crater called Ptah. Dozens of other unnamed craters surround Isis, often overlapping with the sulci linked to the crater. To the south, the large, grooved terrain of Bubastis Sulci stretches between the crater and Ganymede’s south pole. Isis sits inside the Hathor quadrangle (Jg15) of Ganymede, but its northern rays cross into the Apsu Sulci quadrangle (Jg13). Because Ganymede rotates synchronously, the side where Isis lies never faces Jupiter—so someone standing on Isis would never see the planet.
**Morphology** Isis is a bright crater with a pit at its center. It is roughly 75 kilometers (47 miles) wide and at least 2 kilometers (1.2 miles) deep in some spots relative to Ganymede’s average surface level. Unlike most craters on rocky planets or the Moon, Isis and many other Ganymedean craters have a central pit instead of a central peak. The reason is not well understood, but it suggests Ganymede’s surface and subsurface are quite different from those of rocky worlds. Recent studies propose that these central pits form when meltwater, created by the heat of an asteroid impact, collects under the crater floor. As the meltwater refreezes, it expands—water expands when it freezes—cracking the crater floor and causing a pit to collapse, like a sinkhole, especially at the center.
Quick Facts
- Diameter
- 75 km
- Eponym
- Isis
Facts from the source article.
Lore & Background
Isis is named after the Egyptian goddess Isis, who became the mother goddess of Egypt and its most powerful goddess. According to the International Astronomical Union, craters on Ganymede should be named after deities, heroes, and places from Ancient Near Eastern mythologies, and Egyptian mythology falls under this category. Nearby craters such as Osiris and Anubis follow the same Egyptian naming theme. The crater's name was approved by the IAU in 1979.
To Isis's west lies a bright ray crater named Ptah. Dozens of other unnamed craters surround Isis and often overlap with the sulci associated with it. To Isis's south, the grooved-terrain Bubastis Sulci covers the rest of the surface between the crater and Ganymede's south pole. Isis is located within the Hathor quadrangle, but its northern rays cross into the Apsu Sulci quadrangle. The side of Ganymede where Isis is located never faces Jupiter due to the moon's synchronous rotation.
Isis is a bright crater with a pit in the middle, roughly 75 km wide and at least 2 km deep. Unlike most craters on rocky planets, Isis has a central pit instead of a central peak. According to recent studies, these central pits formed when meltwater generated by heat from the asteroid impact refroze and expanded, damaging the crater floor and causing a pit to form like a sinkhole. Six bright sulci radiate outward from Isis, resembling crater rays, but they are not symmetrical or radial; they bend or curve after a few hundred kilometers, resembling the legs of a crab or spider.
Reader's Guide
Isis is significant as a major crater on Ganymede that exemplifies the unique morphology of pit craters found on icy moons, contrasting with the central-peak craters on rocky worlds. The asteroid or comet that created Isis crashed into a dark region of Ganymede's surface, excavating bright, newer materials—mostly clean water ice—that coated a huge portion of the older, dark region, creating a sharp contrast visible today. The crater's rays, which are actually sulci, are notable for their asymmetrical, curved shape, unlike the radial rays of other craters. Isis was first imaged by Voyager 2 in July 1979, as Voyager 1 could not photograph it due to darkness and its position on the opposite side of Ganymede. Later, the Galileo probe studied Ganymede from orbit and flew above Isis several times. Future exploration by the European Space Agency's Juice mission, arriving at Jupiter in July 2031, is expected to provide clearer images of Isis after it enters a low polar orbit around Ganymede.
Did You Know?
- Isis is a bright pit crater located slightly more than two-thirds of the distance from Ganymede's equator to its south pole.
- The crater's central pit likely formed when meltwater from the impact refroze and expanded, damaging the crater floor.
- Isis was first imaged by Voyager 2 in July 1979; Voyager 1 could not photograph it because it was in darkness.
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