A photograph of water on Mars has been posted on the NASA website!

Hold on a second... first of all, what should we consider as "Mars"? The candy itself or the candy in its wrapper?
If "Mars" refers to the candy in its wrapper, then my statement is correct, because the preposition "on" implies some kind of layer between the "Mars" and the glass...
Therefore, we see that there is a glass on the Mars! And in the glass, there is water (or alcohol, depending on your preference :D)! Consequently, there is water (or alcohol) on the Mars!
There you go! :D

Professor, allow me to disagree with your highly respected opinion!
Even if it's a "candy in its wrapper," there is a LAYER in the form of a glass between the "wrapper" and the water itself, as you rightly pointed out. This proves that the preposition "ON" is incorrectly used in the original question. And, therefore, the only correct preposition is "ABOVE" (or "OVER"). :)

And in the next question, colleague, regarding the fact that some people prefer water and others prefer alcohol, I completely agree with you. For example, I personally prefer "Kremliovskaya Vodка." Judging by the fact that it disappeared from sale in 1997, now it can only be found (seen) on Mars! :)