How can we determine the characteristics of life in general, without anthropomorphism?
First, let us make a general remark. What is life? It is, among other things, a complex of coded information. This information, contained in the genes, can be reproduced in an identical way (or almost identical, the errors being essential in the evolutionary process).
The information must have an alphabet to ensure the creation of words describing the information. In nature, we do not know of a more efficient alphabet than that provided by the carbon chains of organic chemistry : these chains are able to describe linearly (and thus legibly according to a fixed order) a very large number of different words.
Indeed, the carbon atom is remarkable in its ability to create complex bonds with itself, or with other atoms to form long molecular chains. An important condition is the presence of water to ensure the creation of bonds..
We have detected such complex carbon chains outside of the Earth, in our own galaxy and in others.
We do not know what other support the alphabet of an extra-terrestrial life form could use.
The vast majority of complex molecules detected in the universe are carbon molecules.