On Sunday, Sept. 29, Earth captured a new "mini-moon" called 2024 PT5. The bus-size asteroid is expected to orbit our planet for 57 days, but is too small to be visible to amateur skywatchers.

If you were hoping to see the “mini moon,” you’ve probably been disappointed. But experts say the asteroid was an important milestone in planetary defense research.

A second moon has officially entered Earth’s orbit—sort of. Although it’s being called a “mini-moon,” it’s actually an asteroid named 2024 PT5. The asteroid has been temporarily captured by Earth’s gravitational pull.