Kittu (crater)

Lore & Background

Kittu crater is located north of Nicholson Regio and east of Barnard Regio along Ganymede's equator, within the chaotic, grooved terrain of Mysia Sulcus. It lies on the side of Ganymede that always faces Jupiter, near the Subjovian point, meaning an observer inside the crater would always see Jupiter nearly overhead. The crater is part of the Misharu quadrangle (Jg10), and a crater with the same name as the quadrangle lies to its south.

Kittu exhibits a bright, white central peak and rim, but is surrounded by dark, brownish materials, classifying it as a dark ray crater. Its dark rays are sprinkled atop the surrounding grooved terrain. The dark material may be from an impactor (asteroid or comet) that contaminated water ice, or may originate from about 1.2 km below the surface within Ganymede itself. The dark ejecta has a reflectance of 6% in the near-infrared, the lowest of all dark ray craters on Ganymede, and consists of an approximately 50/50 mixture of carbonaceous material and hydrates. The impactor hit grooved terrain, and a straight segment of the rim resulted from collapse along an older fault line.

A study by Baby suggests Kittu is the youngest crater within the Mysia–Harpagia unit. Models place its age between 0.2 and 1.5 billion years (lunar-derived model) to less than 100 million years (Jupiter–comet model). Other examples of dark ray craters on Ganymede include Antum, Khensu, and Nergal.

Reader's Guide

Kittu crater is significant as one of the best-photographed dark ray craters on Ganymede, thanks to high-resolution images taken by the Galileo probe during its 7th orbit at a spatial resolution of 3 km per pixel. Its dark ray system is rare on Ganymede, and its ejecta is the darkest of all dark ray craters, with a flatter and redder spectrum at visible to near-infrared wavelengths. The crater's dark materials may provide clues about Ganymede's subsurface composition, as recent studies suggest the rays originate from within the moon rather than from external impactors. However, the source remains uncertain, as carbonaceous material could also accumulate from long-term impactor debris. The Voyager 1 first imaged Kittu in March 1979, and the Juno spacecraft captured decent photographs in June 2021 during a close flyby. Its small size and dark appearance make it difficult to see, but its unique properties make it a target for future missions to determine the origin of its dark materials.

Did You Know?

• Kittu is named after the Mesopotamian goddess of truth, justice and the law, Kittu (also known as Kittum).
• Its dark ejecta has a reflectance of only 6% in the near-infrared, the lowest among Ganymede's dark ray craters.
• An observer standing inside Kittu crater would always see Jupiter nearly overhead due to Ganymede's synchronous rotation.
• The crater's dark rays may originate from about 1.2 km below the surface, rather than from the impactor that formed the crater.