For space and solar system related media website
Creating online news, magazine or blog that is all about the planetary body for consumption of interested people will surely gain more traction is it was created using a .SPACE domain. The .SPACE domain name makes it quite possible to relate you website easily with the solar system space.
For planetarium website
Bring your planetarium online with a .SPACE domain name. Sometimes people just need to get information on subject matters that could be found at your planetarium alone, you could easily save those set of people from the stress of having to transport down to your location. You could easily start selling an online subscription of pass for such people at same price as the people visiting physically. That way you will reduce unnecessary stress and risk of life, and you will also make more money in the process.
For private or personal website
The word personal or private space is self explanatory on its own. Using the .SPACE domain extension for websites like a personal journal or diary would be highly effective in portraying what the website is. It will also be a perfect means of using a catchy and creative domain name for your website. Example is in the case of YOUAREINMY.SPACE, JOHNS.SPACE etc.