What explosion had an altitude of 539 km?
CREATE TABLE table_19624 (
    "Explosion" text,
    "Location" text,
    "Date" text,
    "Yield (approximate)" text,
    "Altitude (km)" text,
    "Nation of Origin" text
)
SELECT "Explosion" FROM table_19624 WHERE "Altitude (km)" = '539'
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: What explosion had an altitude of 539 km? ### Input: CREATE TABLE table_19624 (
    "Explosion" text,
    "Location" text,
    "Date" text,
    "Yield (approximate)" text,
    "Altitude (km)" text,
    "Nation of Origin" text
) ### Response: SELECT "Explosion" FROM table_19624 WHERE "Altitude (km)" = '539'