MY7 VS5 EH5 M?! What do ? and ! Stand for ?

Can u CRACK THE LOGIC ...???

MY7
VS5
EH5
M?!
JR7
SN6
US6
NE7

What do '?' And '!' Stand for?

Challenge all master brains!
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These are actually the Planets of our Solar System
Mercury = MY7 (First and Last Letter and the total Number of Alphabets)
So M?! = Mars = MS4
So the answer is ? = S and ! = 4