The mapping principle of JANUS
The mapping principle of JANUS
A distinctive feature of JANUS is its wheel with 13 filters in different colours that can be rotated in front of the telescope. Each filter allows JANUS to detect different concentrations of chemical elements. For example, red indicates methane and yellow sodium. In the near-infrared, JANUS can detect rock-forming minerals and salts on the moons - here using Ganymede as an example.
