Callisto

https://www.universetoday.com/57581/callisto/https://futurism.com/space-habitats-and-the-oneill-cylinder/

https://www.universetoday.com/130637/colonize-jupiters-moons/

http://space.alglobus.net/Basics/where.htmlhttps://www.windows2universe.org/jupiter/moons/callisto_interior.html

http://colonyworlds.com/2007/08/jupiters-callisto-gateway-to-the-gas-giants.html

https://space-facts.com/callisto/https://solarsystem.nasa.gov/planets/jupiter/moons

https://science.nasa.gov/science-news/science-at-nasa/1998/ast22oct98_2

https://solarsystem.nasa.gov/planets/callisto/gallerieshttps://theplanets.org/callisto/

https://en.m.wikipedia.org/wiki/Callisto_(moon)

http://solarviews.com/eng/callisto.htm

https://www.space.com/16448-callisto-facts-about-jupiters-dead-moon.html

http://amazingspace.org/resource_page/115/solar_system/type

https://www.solarsystemquick.com/callisto.htm

https://www.astronomytrek.com/10-interesting-facts-about-callisto/

http://study.com/academy/lesson/jupiters-moon-callisto-facts-lesson-quiz.html

https://www.solarsystemquick.com/callisto.htm

http://astronomyonline.org/SolarSystem/Callisto.asp

https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA01054https://books.google.com/books?id=cWh706GfE9EC&pg=PT211&lpg=PT211&dq=har+crater&source=bl&ots=5VHCxHoiJu&sig=z5tWeMyi6lskFMJFEXYbd5xvZSc&hl=en&sa=X&ved=2ahUKEwjLuP7ugqPZAhURmeAKHZTUAo8Q6AEwDHoECAkQAQ#v=onepage&q=har%20crater&f=false

https://science.nasa.gov/science-news/science-at-nasa/1998/ast22oct98_2

https://solarsystem.nasa.gov/moons/jupiter-moons/callisto/in-depth/

http://homepage.usask.ca/~mjr347/prog/geoe118/geoe118.034.html