XMM is still extremely useful. There was a recent report that using clever techniques ESA are going to keep it going for another 10 years: https://www.esa.int/E

XMM is still extremely useful. There was a recent report that using clever techniques ESA are going to keep it going for another 10 years: https://www.esa.int/Enabling_Support/Operations/Teaching_an_old_satellite_new_tricks https://www.esa.int/Enabling_Support/Operations/Teaching_an_... XMM has a smaller field of view than eROSITA, but more light gathering capability (effective area), particularly at higher energies. It also has different types of instruments, such as the X-ray gratings. eROSITA is really designed for doing surveys with its wide unobstructed field of view, and it will be doing just that for the next 3.5 yrs. We really need XMM to follow up in detail the most interesting sources we discover during the survey.