I read this in 2000 or 2001. I think it was a novel, although it could have possible been a short story.

A small group of people is exploring a moon (Titan?) using a pair of virtually piloted un-manned gliders/planes. I remember that one of the crew was terminally ill. They found some weird "tar pools" that turned out to be quasi-lifeforms(?), and I think there was some sort of accident where a woman was absorbed by one of the pools and the dying man later flew into it intentionally.

I believe this was written by one of the same authors who contributed stories to Far Horizons (I somehow came to one book through the other?), but I can't remember who (I am positive it wasn't Brin. Certainly not McCaffrey. It doesn't really seem like Le Guin.), and I can't find any descriptions of anything like this that they have written. Maybe I'm just looking in the wrong places...

Thanks!