Several ambitious initiatives, such as Destination Earth of the European Union, are harnessing large amounts of Earth Observation and other data to develop so-called digital twins of the Earth. The combination of large and diverse data assets, cloud- & HPC-computing as well as sophisticates models and AI algorithms now permit to generate predictive EO scenarios. One key aspect of Digital Twins is the possibility to employ openness as one of the key principles for all its functions. Data policy, data access, software development, processing and information management are important considerations for engaging and integrating users of all kinds. Due to their high potential for science and society the European Space Agency, with its unique geospatial data holdings, is fully engaged in the development of Digital Twins of the Earth.