The reason that this simulation was removed is because you can now compare the bodies of any system using the "Chart Mode" feature.
- Open any System
- Right click to open the control panel.
- Click "Chart Mode"
- Right click again to change the sort order for this list (Mass, Density, Diameter)
Note that not all bodies have a valid mass or diameter (so some of them may bunch up at one end).
You can see a screenshot of this feature here:
http://universesandbox.com/about/(3rd picture from the top)
Open up "Stars - Within 16 parsecs" (or any simulation with some stars)
Change the Chart Mode to "Stars" to view a Hertzsprung–Russell diagram.
http://en.wikipedia.org/wiki/Hertzsprung-Russell_diagramI'm currently working on simplifying the user interface. The chart mode feature will be much more obvious and easy to use in a future release.