Complex sentence: In 1991, a European satellite called ERS-1 turned its high-frequency array toward the center of the Antarctic ice cap and it confirmed the 1973 discovery of a large lake below four kilometers of ice, named Lake Vostok.
Split into simpler sentences: In 1991, a European satellite called ERS-1 to turn its high-frequency array toward the center of the Antarctic ice cap. It confirmed the 1973 discovery of a large lake in Antactica below four kilometers of ice, named Lake Vostok.