Two mysterious flashes have been spotted on the moon’s surface, sparking a debate over what just struck our nearest neighbor in the solar system.

Astronomer Daichi Fujii, curator of the Hiratsuka City Museum in Japan, captured the first of these bright flashes on October 30, revealing a large round dot briefly illuminating the moon’s surface before disappearing.

The second flash was spotted two days later, on November 1, near the moon’s horizon from Fujii’s perspective here on Earth.

Read more: Mysterious flashes on the moon spark speculation about unknown visitors