This is the video of the close encounter of Asteroid 2019 OK we have been Twitting all day with the Earth: https://t.co/bjT7uhQJuO pic.twitter.com/3e4UyPcdPl
— ASAS-SN (@SuperASASSN) July 25, 2019
We have been getting a lot of close calls with asteroids of late, with each one drifting ever nearer our terrestrial space. The most recent one happened last Thursday when Asteroid 2019 OK sped past the Earth at a distance of about 70,000 kilometers which might seem far but it's a lot closer to us than the Moon.
Due to the trajectory of the asteroid – flying towards us from the direction of the sun – astronomers had no warning it was headed our way. It is the largest rock to fly at such close quarters to the Earth this year, and possibly for many years.
Astronomers believe the asteroid is between 57 and 130 metres in diameter. Telescopes only began to pick it up a couple of days ago, with a confirmation it was an asteroid only coming in the past 24 hours.
Had it been on a collision course with Earth, its impact would have decimated a city, according to astronomers. There were other asteroids who had also passed by Earth but 2019 OK was the closest. -via PS Mag
(Image credit: ASAS-SN/Twitter)
I doubt a impact of "30x Hiroshima" would generate a destructive Tsunami if it did land at sea, since it'd likely be exploding on-or-above the surface instead of creating an underwater landslide. It's also not clear what the composition of this thing was -- a lot of damage estimates from asteroids are based on the "worst case" of a solid nickel-iron chunk, while most such objects are stony or even more loosely composed, like balls of boulders and gravel. Objects like that would tend to break up in the upper atmosphere, and while they might do some significant damage on the ground (a'la Tunguska), it's a lot less damage than a solid projectile would do.
So, 2019 OK actually hitting the Earth wouldn't have been a good thing, But it would still have been more likely not to hurt anyone than to wipe out a city.