My very eager mother just served us nine pizzas...
Why did she do it?
My Very Eager Mother Just Served Us Nine Pizzas.
Taking the first letter of each word in the above sentence, this becomes:
M V E M J S U N P where:
M=Mercury
V=Venus
E=Earth
M=Mars
J=Jupiter
S=Saturn
U=Uranus
N=Neptune
P=Pluto
This is a proposed mnemonic to remember the name of the 9 planets prior to 2006 AD.
However, Pluto ceased to be a planet from the year 2006 and is presently considered a dwarf planet.
Accordingly, it seems that this puzzle must have originated before the year 2006.