Reifnir
What Reifnir is
Reifnir is a crater — a circular depression, almost always an impact scar — on Callisto, 36.8 km across, centred at 50.8° S, 54.3° W. It is the 135th largest named feature on Callisto and the 122nd largest of its class there.
Where the name comes from
Ottar's ancestor. The International Astronomical Union approved the name in 1997, under the theme it applies to every crater on Callisto. Of the 141 features of this class catalogued on Callisto, the naming categories run Norse (70), Finland (12), Norway (10), Eskimo (9).
What it would take to settle Reifnir
Callisto scores 44.6 as a world. That number is the same for every square metre of it — but sunlight, water, radiation and the ground under your feet are not. This is the same question asked at 50.8° S, 54.3° W.
What this spot has going for it is water — same as everywhere else on this world. What works against it is temperature — about -146 °C mean at this latitude.
Computed from Reifnir's catalogued latitude, longitude and feature class — 84% of the model's weight had a basis here, and 2 axes were dropped as not applicable to Callisto (earth link, known ground). Gravity, pressure, delta-v and distance from the Sun are the same everywhere on Callisto and are already counted in the world's own index, not again here.
What this cannot see: elevation. Slope, local shadowing and the polar “peaks of eternal light” — ridge tops near the poles of a barely tilted world that catch sun almost continuously while a crater floor kilometres away never does — need a terrain model this does not have. Where a real mission targets a pole, that is usually why.
What is next to it
The largest crater features on Callisto
All 141 craters on Callisto — mapped together, with the naming theme and the size distribution.