| M Y V S E H M S J R S N U S N E P
M V E M J S U N P <<< Every other letter starting with M are the first letters of the planets
Y S H S R N S E <<< Every Other letter startin with Y are the last letters of the planets
The anser is O as that's the last letter of Pluto:
MercurY VenuS EartH MarS JupiteR SaturN UranusS NeptunE PlutO |