COunt the average Diameter (km) which has ketian (yenisey r.) main evil goddess.?
CREATE TABLE "fossae" (
  "name" text,
  "latitude" text,
  "longitude" text,
  "diameter_km" real,
  "year_named" real,
  "name_origin" text
);
SELECT AVG("diameter_km") FROM "fossae" WHERE "name_origin"='ketian (yenisey r.) main evil goddess.';