The inner core is solid because it is made of very dense, or heavy, materials - like iron and nickel. Even though it is very hot, these materials don't "melt" very easily, so they stay solid. Answer 3: It turns out that many materials can be a solid at a higher temperature if the pressure is also higher.

Development of SpaceEngine began in 2005,[8] with its first public release in June 2010. The software is written in C++. The engine uses OpenGL as its graphical API and uses shaders written in GLSL. As of the release of version 0.990, the shaders have been encrypted to protect against plagiarism. Plans have been made to start opening them in a way that allows the community to develop special content for the game, with ship engine effects being made available to users who have purchased the game.[9]

On May 27, 2019, the Steam store page for SpaceEngine was made public in preparation for the release of the first paid version, 0.990 beta.[10]

SpaceEngine is currently only available for Windows PCs; however, Romanyuk has plans for the software to support macOS and Linux in the future.[11]