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.

Though it can’t be seen with the naked eye or binoculars or a home telescope, but it can be visible to professional equipment because of its small size and made of dull rock.

On Sept. 29, the Earth will temporarily get a second moon. A small asteroid will be pulled into orbit before being released from our planet’s gravitational pull. NASA’s Asteroid Terrestrial-Impact Last Alert System (ATLAS) spotted the little asteroid on Aug.