Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_148578_1 (explosion VARCHAR, altitude__km_ VARCHAR)
### Question:
What explosion had an altitude of 539 km?
### Answer:
SELECT explosion FROM table_148578_1 WHERE altitude__km_ = "539"