The Metis coronagraph
Metis is the coronagraph of the scientific payload of Solar Orbiter, the first mission of the European Space Agency program Cosmic Vision 2015-2025. Solar Orbiter has been conceived to explore for the first time the poles of the Sun and the circumsolar region. The spacecraft launch is foreseen in February 2020.
The main Metis objective is the investigation of the global corona in polarized visible light and in ultraviolet light. In the ultraviolet band, the coronagraph obtains monochromatic images in the Lyman-α line, at 121.6 nm, emitted by the few neutral-hydrogen atoms surviving in the hot corona.
By simulating a solar eclipse, Metis observes the faint coronal light, at least one millionth dimmer than the disk light, in an annular zone 1.6°–2.9° wide, around the disk center. When Solar Orbiter is at its closest approach to the Sun, at the minimum perihelion of 0.28 AU (i.e., astronomical unit), the annular zone is within 1.7 and 3.1 R☉ (solar radii) from disk center.
Futher information can be found in the Metis paper on the Solar Orbiter mission book.