If Oumuamua had been on a collision course with Earth, we would have had no warning. It had already passed us when it was discovered on 19 Oct. The impact would have been a week earlier on 14 Oct, unleashing an explosive yield equivalent to about 30 megatons of TNT.
Related: we’ve separately published a detailed report analysing the evidence indicating that Oumuamua is an extraterrestrial vehicle.
Nukemap estimates that an explosion of that magnitude has an air blast diameter of about 8 miles, within which there is a 100% fatality rate and near total destruction of buildings over an area of 55 square miles. Far beyond the main impact, people would receive third-degree burns over an area exceeding 2000 square miles. To put this into context, if it hit Beijing there would be over 7 million casualties with 5 million people killed by the immediate blast, and many more affected by the after-effects of the cataclysm.
If Oumuamua had landed in the ocean, it could have triggered a megatsunami. Russia has studied this while developing tsunami weapons. According to the Russian Geopolitical Academy, a 100 megaton warhead can produce a tsunami 500m high wiping out all living things up to 1,500km into US territory.
In 2029, on Friday, 13th April, asteroid Apophis could hit us with an impact of 880 megatons. That could produce a mega-tsunami over a mile high, a phenomenon that hasn’t happened on Earth during the short time our species has been around. Nasa admits that it “cannot rule out” an impact with Earth. Apophis will certainly pass closer to Earth than some of our communications satellites. If it misses us, it could hit in 2036. Do the math: this could be an extinction-level event. What are we doing about it? Nothing much. As a species, we’re focusing on other things, like watching celebrities on TV. Perhaps that’ll win us the Darwin award for Terrestrial Species Most Unfit to Survive.
But Oumuamua serves as a sobering reminder to us all that the most dangerous objects are those we don’t see coming.