chasma

The most prominent tectonic feature on Tethys is the globe-girdling Ithaca Chasma, which is 60 to 100 km wide, 3–4 km deep, and can be traced through at least 270° of a rough great circle (Smith et al, 1982; Moore & Ahern, 1983). […] Odysseys Tangent Chasma. A prominent chasma 60–80 km wide and at least 800 km long (90° arc), visible in 80.27, is tangent to the rim of Odysseus, trending about 10° east of north. The chasma intersects a ridge-bounded trough radial to Odysseus […] and is then lost in the zone around the North Pole that is shadowed in all of the extant images.

Thus Cornelius Gemma, Professor of Medicine in Louvain, mentions them [the aurora borealis] under the name of chasma, as appearing in Brabant on the 13th February and 28th September, 1575.