There should be an another Sun and earth very long distant.

No one can ensure after the death we will be born as a human under this Sun only.There is a possibility that another Sun is available in long distant where we do not have technology to reach that Sun and the earth they also may also not be able to reach us due to lack of technology.
Whether it is possible to born two Lord Buddhas in such two world system one time is an issue of the nature.Sometimes possible sometimes impossible.