On June 30, 1908, a large explosion occurred near the Podkamennaya Tunguska River in Siberia. Around 2,150 square kilometers (830 square miles) of the Siberian forest was flattened, tremors were detected as far as the UK and the US, and three people may have died. The explosion is believed to have released 30 megatons of energy, enough to level a city.
The cause of the event originated outside Earth. A space body entered the atmosphere, disintegrated, and the shockwave produced led to the cataclysmic event. However, a new study published in the Monthly Notices of the Royal Astronomical Society has provided a slight tweak to that scenario. What if the space body never disintegrated but instead rebounded back into space? The team envision an asteroid hitting the atmosphere like a stone skipping on a lake, producing the shockwave that flattened all those trees.
The idea, although peculiar, may explain several odd features about the Tunguska event. Researchers have found no evidence of an impact crater (the nearby "impact" lake is now believed to be older) and there is a distinct absence of meteoric material near the epicenter of the event. In the study, the bolide in question may have instead crossed the atmosphere, reaching an altitude as low as 10 to 15 kilometers (6 to 9 miles) before continuing its journey through space.
The team looked at space bodies 200, 100, and 50 meters (656, 328, and 164 feet) in size and composed of different material: iron, rock, or ice. Passage through the atmosphere is brutal, with friction from air resistance creating incredible temperatures. Ice and rocky bodies would not survive. An iron one, however, might with minimal mass reduction, coming in at a shallow angle and keeping its speed over the Earth’s escape velocity.
“At present, there are over 100 hypotheses about the nature of the Tunguska phenomenon, among which three to four versions are predominant theories,” wrote researchers led by astronomer Daniil Khrennikov of the Siberian Federal University in the paper.
So how does this paper measure against them? The work is focused on investigating the possibility that a space body can enter Earth’s atmosphere and continue on its trajectory away from Earth mostly unscathed. The team showed this is possible under certain conditions. The findings are exciting but there are several limitations, including the fact they did not simulate the formation of the shockwave but used calculations from the Chelyabinsk meteorite event and previous research from 1966. They plan to investigate the scenario in more detail in future work.
For now, the origin of the Tunguska event remains shrouded in mystery.
[H/T: Science Alert]