Valhalla (crater)

Located on Jupiter's moon Callisto, Valhalla (/vælˈhælə/ val-HAL-ə)[1] is the largest multi-ring impact crater in the Solar System.

The multi-ring system may have formed as semi-liquid or liquid material underlying the brittle lithosphere punctured by the impactor slumped towards the center of the crater following the impact.

[4] It was discovered by the Voyager probes in 1979–80 and is located on the leading hemisphere of Callisto, in its Jupiter facing quadrant slightly to the north of the equator (at about 18°N latitude and 57°W longitude).

At the high resolution achieved in some Galileo images the central part of Valhalla looks like a knobby terrain, where bright knobs are surrounded by dark smooth plains; there is noticeable deficit of small impact craters.

These scarps, when studied at a high resolution, turned out to be discontinuous consisting of a series of small bright knobs surrounded by the smooth dark material.

[2] Consistent with this picture, imaging by the Galileo spacecraft found no evidence of disruption of the area of Callisto antipodal to Valhalla.

The absence of such disruption supports the presence of a subsurface ocean, which would have absorbed much of the seismic energy, at the time of Valhalla's formation.

[8] Kim Stanley Robinson's Galileo's Dream (2009) contains a detailed description of a large city built around the concentric rings of Valhalla in the 29th century.