Ligeia Mare is a lake on Titan at 79.0 Â N , 248.0 Â W , measuring around 500 km in width . Ligeia Mare is a lake composed of liquid hydrocarbons ( mainly methane ) on Titan at 79.0 Â N , 248.0 Â W , measuring approximately 500 km in diameter and with surface area of about ~ 100,000 km2 .