- The apples that detach from the tree.
No I don't think it means what you said. I think it can mean apples that (by their own capacity) detach from the tree. Of course, this doesn't really make sense since apples can't really do anything themselves. Another thing it could mean is apple that (have the capacity) to detach from trees. Of course, this seems true for any apple.
- It means that apple gets detached from the tree.
you might say
- The detached apples
if it is understood that you are talking with respect to trees, or
- The detached apples from trees
though 4. sounds strange to me.
- The vast majority of the sampled grains originate from active jets that spray from the surface of Saturn's geologically active moon Enceladus.
Let us examine a definition of jet.
a (1) : a usually forceful stream of fluid (as water or gas) discharged from a narrow opening or a nozzle
(2) : a narrow stream of material (as plasma) emanating or appearing to emanate from a celestial object (as a radio galaxy)
Let us look at an image of some jets.
In 5., spray means
: to project spray or something resembling spray on or into
Other ways to understand spray in 5. are shoot, spout, originate. In other words, 5. is saying that the jets (the streams) originate/shoot from the surface of Saturn's moon "Enceladus". So, the jets are not "getting" spray, but instead they are escaping/shooting from the surface. If you meant something like "getting shot from the surface", then you had the right idea.
People bend and break the rules of grammar all the time. I don't know if the rule says you "must" put a comma there, or if you should put a comma if the meaning is ambiguous without it. I also remember it as "it should be there", but since the sentence is understandable (at least to native users) without the comma, then it really doesn't matter that the author broke the rule.