This is just a random thought here, but Is in conciveable that a planet that is not naturally inhabitable requires a senshi. Once a matrix for linking something to a Senshi is setup the Senshi acts like a climate control system, or rather their Sailor Crystal, and this works both ways, the health of one affects the health of the other and they help the other to heal. If the Senshi dies then the planet will, or atleast become uninhabitable. the same way with Stars, with the Senshi dead, the star destabilizes. Thus there are methods in place that cause a replacement to be born or get chosen when one dies.
This could mean that the act of sending the senshi forward would have caused the other planets to 'die' when the senshi were sent forward. Add in that time travel does affect a planet negitively, but it can take a little while for anything bad to happen. and we have a contengance that allows to know that the Senshi is still alive just displaced.
I am asking this for a fic idea where someone is attacked because they are the senshi of the Sun, even though their ancestors hadn't transformed since the Silver mellinium. the attacks are an attempt to damage the sun.