[TeMPOraL]

I can't be 100% certain because we don't understand consciousness yet, but I believe we can derive some logical conclusions.

Starting from the basics: life is just complex, carbon-based nanotechnology. There's nothing we know that suggests cells are anything more than complex machines. There's nothing suggesting that if you put a bunch of cells together, you get something more than a complex machine. From the other end, we're only sure that conscious experience happens in human brains, though through structural and behavioral similarity, we may assume some degree of conscious experience in a lot of animals. Going this route, around smaller insects you may start to wonder whether what you're looking for is more like a machine, or more like a feeling thing capable of experiencing emotions. Plants are biologically less complex than insects, and have no identifiable "locus of cognition".

I mean, you have to note that when guessing whether or not something can experience emotions, we're projecting our own mental states based on that thing's phenotype. Look how works of fictions - pictures, movies, even textual descriptions in books - can make you feel compassion towards a rock, or a car. A skilled writer could rephrase my fighter jet example in a way that would make you actually feel sorry for it. This means our intuition is not a good judge here. Past that, the best we have (AFAIK) is heuristics, like "has no brain/brain-level complexity = probably can't have experiences".