Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Explosion | Location | Date | Yield (approximate) | Altitude (km) | Nation of Origin |
| --- | --- | --- | --- | --- | --- |
| Hardtack Teak | Johnston Island ( Pacific ) | 1958-08-01 | 3.8 megatons | 76.8 | United States |
| Hardtack Orange | Johnston Island ( Pacific ) | 1958-08-12 | 3.8 megatons | 43 | United States |
| Argus I | South Atlantic | 1958-08-27 | 1-2 kilotons | 200 | United States |
| Argus II | South Atlantic | 1958-08-30 | 1-2 kilotons | 256 | United States |
| Argus III | South Atlantic | 1958-09-06 | 1-2 kilotons | 539 | United States |
| Starfish Prime | Johnston Island ( Pacific ) | 1962-07-09 | 1.4 megatons | 400 | United States |
| K-3 | Kazakhstan | 1962-10-22 | 300 s kiloton | 290 | USSR |
| K-4 | Kazakhstan | 1962-10-28 | 300 s kiloton | 150 | USSR |
Question:
What explosion had an altitude of 539 km?
Answer:
Argus III