Another weak point of a liquid mirror is that it cannot benefit from the adaptive optic technology, which has drastically improved the resolution of Earth-based telescopes over the last two decades. The technique uses a honeycomb array of smaller mirrors instead of a single big one, with each tile set on an actuator, which can tilt it a couple of microns around two of its axis.

A sensor detects atmospheric distortions in the incoming light before it hits the mirror, while a computer processes the information and deforms the mirror to compensate for it. The result is better sharpness of an image.

Now scientists at Université Laval in Quebec have built a liquid mirror version of adaptive optics. They used non-toxic ferromagnetic liquid covered by a reflective film instead of mercury and an array of 91 magnetic actuators to distort the mirror.

They also used a trick suggested by another team to avoid a big weakness of magnetic actuators. The deformation they produce is proportional to square of the strength of the magnetic field, while computer algorithms used in adaptive optics systems are linear. To linearize the response, researchers used superimposition of a strong uniform external magnetic field with the fields created by the actuators.

The team also used a novel liquid which allows the use of higher frequency magnetic fields. Until recently deformable ferromagnetic liquid mirrors were thought to be restricted to corrections at 10 Hz, and the new approach boosted it to 1 kHz.

A larger mirror using the technology would rival glass counterparts in both cost and smoothness of surface, authors say. It will still be able to look only at a zenith, however.