Personally, I find Brown Dwarfs to be absolutely fascinating. An object that isn’t quite a planet and isn’t quite a star, but something in between.
What would one even look like? Would it look like a gas giant that’s glowing red, along with swirls of gas in its atmosphere like Jupiter? Or would it resemble a star and have a fiery surface like the sun? I prefer to imagine them as glowing gas giants but I don’t know how realistic that is.
Gas giants in general are fascinating to me as well, I really hope we send a probe into one of the gas giants with a camera before I die. I’d absolutely love to see what it looks like inside a gas giants atmosphere before the probe gets crushed by the increasing pressure as it descends.
Imagine if we found even simple single celled life in the subsurface oceans that are theorised to exist beneath their surfaces. It’d be the single biggest discovery in the history of humanity IMO even if it’s just bacteria.
If we find life somewhere else in the solar system, it will be interesting to see if we are related to it, or whether it developed independently.