Answer: 30 June
Notes: The world celebrates June 30 as World Asteroid Day to mark the Tunguska event, a huge asteroid explosion over Siberia, Russia, in 1908. The Tunguska event flattened about 2,000 square kilometres of forest with energy equal to 185 Hiroshima bombs. World Asteroid Day aims to raise awareness about asteroid risks and encourage investment in space science and technology. The United Nations General Assembly passed resolution A/RES/71/90 in 2016 to declare June 30 as International Asteroid Day after a proposal from the Association of Space Explorers, supported by the Committee on the Peaceful Uses of Outer Space (COPUOS).
