It's always a bit jarring to see scientific data presented in non-metric units, even in the US. But as an American, I only understand density in terms of Libraries of Congress per Olympic Sized Swimming Pools
What is the base unit of "Libraries of Congress per Olympic Sized Swimming Pools"? Does the expansion rate of the LoC match the expansion rate of the universe?
It's clearly in Celsius, which is the metric system's temperature unit and it is clearly stated on the website's about page:
By default the page loads and displays distances in miles, temperatures in Fahrenheit, ie English units (also known as Imperial or USCS system units). If you wish to have the page load and display in kilometers and temperatures in Celsius, ie metric system units use the urls below to select your preferred units.