This is where Musk and SpaceX have been planning for years. Where other rockets have used space grade kerosene (RP1) and liquid oxygen, or liquid hydrogen + oxygen, Musk knew he wanted to refuel natively from the Martian atmosphere, which is CO2 rich, then the best fuel would be methane and oxygen. Hence the new raptor engine burns methane amd oxygen. Plus the Starships can be configured as fuel browsers, freighters, human-rated travel or as "Pez" dispensers fir hundreds of Starlink satellites per launch. The goal is to fund interplanetary missions from massive commercial benefits of launching satellites around Earth, then to build a fleet of vehicles capable of hundreds of trips each ship, then refuel in Earth orbit to allow much bigger missions to Mars than could launch direct from Earth. And so on... its incredible really.