Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_148578_1 ( explosion VARCHAR, altitude__km_ VARCHAR )

### Question ###
What explosion had an altitude of 539 km?

### Accurate SQL ###

SELECT explosion FROM table_148578_1 WHERE altitude__km_ = "539"