When light from space passes through the atmosphere it degrades, giving earth-based telescopes a murky picture of the cosmos. To compensate, adaptive optics systems employ either very thin, pliable mirrors or honeycomb arrays of tiny hexagonal mirrors that can be adjusted to compensate for the light degradation, undoing the effects of atmosphere on light.
Liquid mirrors, however, could come back into fashion in a big way thanks to some developments that make them act like adaptive optics systems without requiring the adaptive optics price tag. Using a ferromagnetic liquid (rather than mercury), researchers pioneered a novel way to create deformable liquid mirrors a few years back, but there were some problems. For one, the magnetic fields used to deform the liquid couldn't be cycled quickly enough to be useful in astronomy. For another, there was a non-linear disconnect between the deformation of the mirror and the magnetic field strength that required a highly complex algorithm to be built from scratch.