New study explains why intelligent aliens may never reach for the stars.

Many exoplanets have vast oceans under kilometers of ice. These are “fishbowl worlds”. Their inhabitants may never see the stars, so will lack motivation to reach them. Simple sounds travel tens of kilometers in water, so the inhabitants may never feel the need to develop communication technologies. Such intelligent beings may forever remain beyond our ken.

The author of this scientific paper could well be describing our own oceans, not those of some distant planet.