Identify the informal fallacy in the argument: 'No one has ever given an indubitable proof regarding the impossibility of life on Planet X, therefore one can conclude that there is life on Planet X'.

The argument is an appeal to ignorance.

It concludes that there is life on Planet X.

The only ground is that its impossibility was never proven.

Failure to disprove a claim is taken as proof of that claim.

Treating absence of counter-proof as evidence is the appeal to ignorance.