Hmm, I'm not so sure. For two reasons: If we assume that life naturally arises when light is shone at rocks for long enough then we might assume that life on mars would have an independent origin. However, this does not necessarily mean that life there will have orthogonal biochemistry. It may be that the biochemistry we observe on earth is the biochemistry most likely to emerge in a wide range of environments.

On the other side we should consider the possibility that space is porous to life. That life is able to travel between bodies or on bodies that pass through the vacuum of space. In this case we should expect that while there may be independent origins of life, within relatively short distances a certain kind of biochemistry might come to dominate.

Add to this the quite important role that exogenous organic chemicals likely played in the emergence of life on earth, in the case where life arose here and on mars independently. It is probably more likely that life would emerge through roughly the same processes wherever it emerges, therefore in roughly similar environments and using roughly the same building blocks (organic molecules constructed in space and deposited through impacts) we might expect it to have similar forms. I would say that Titan is likely to have something entirely different to earth life - owing to it's very different environment...

That's unlikely, in my opinion. There are some seemingly fundamental aspects to the underlying mechanisms of life as we know it today and some aspects that are mostly just accidents of history. For example, RNA/DNA type systems and polypeptide proteins represent enormously powerful designs which seemingly can be bootstrapped from simpler systems. It would not be at all shocking to see other forms of life based on very familiar machinery. But if there were different details here and there, that too would also not be surprising.

Additionally, electrochemical gradients as a means of storing and using energy, and amphiphilic bilayer based membranes both seem to be incredibly fundamental, it would be more surprising to see life that was based on other principles than to see life that shared the same design. As for everything else, who knows? It's likely there are a ton of alternative design choices for a lot of different aspects of cellular machinery on up to large scale structures of plants, animals, fungi, etc.

But overall I'd rate some of the more "out there" notions of things like silicon or sulfur based life, or merely carbon-based life that was utterly different from our nucleic acid/protein/membrane based life as being comparatively unlikely.

Alternate possible biochemistries are dependent on the stability & potential variations in bonding: https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemi...

Other than the possibility that the origins of life and potential life on Mars are the same, I think the same thing as you.

Imagine it is completely distinct, and doesn't have cells.