The “city killer” rock that no one warned us about

By Robert A. Vella

Last Thursday, an asteroid roughly 328 feet in diameter – large enough to wipe-out an entire city – barely missed hitting our planet.  It wasn’t noticed until two days before passing by Earth at about one-sixth the distance to the Moon.  That’s close, folks.  That’s so close that it is known as a cosmic “near miss.”  Although it’s understandable why this asteroid hadn’t been previously observed, it is not so understandable why the public wasn’t informed about it until two hours before closest approach.  But, on second thought, an immediate announcement might have triggered panic in the region of potential impact since nothing at all could’ve been done to divert the asteroid.  Anyway, here’s the story plus a scientific estimation of what an observer would experience standing on Delaware’s Atlantic coastline 50 miles from an oceanic impact.

From:  How Astronomers Missed the Massive Asteroid That Just Whizzed Past Earth

A large asteroid just whizzed past our planet — and astronomers weren’t expecting it.

Ranging in size from 187 to 427 feet (57 to 130 meters) wide, the space rock named 2019 OK snuck up on us Thursday morning (July 25). It swung as close as 45,000 miles (73,000 kilometers) from Earth, what one astronomer told The Washington Post was “uncomfortably close.”.

If the asteroid had actually collided with Earth, the crash would have caused devastating damage, Michael Brown, an associate professor in astronomy at Monash University in Australia, wrote in The Conversation.

Astronomers in Brazil and the United States separately discovered 2019 OK a couple of days ago, but it’s surprise visit was only announced a couple of hours before it passed by. “The lack of warning shows how quickly potentially dangerous asteroids can sneak up on us,” Brown wrote. And though this asteroid “is not a threat to Earth right now,” other such near-Earth asteroids can be.

From:  Asteroid 2019 OK 328-feet-wide rocky object came very close to Earth HOURS ago but did not collide

On Thursday early morning, our planet Earth close encounter with a giant asteroid. A 328-feet-wide asteroid 2019 OK zoom past the Earth on 6:52 am (IST) today at a speed of nearly 55,000 miles (88,500 kilometres) per hour. Space rock can cause tsunamis, shock waves, and flattening winds,that could be catastrophic.

From:  The day Earth had a near-miss with a ‘city-killer’ asteroid

By comparison, the rock that killed the dinosaurs was about 16 kilometres across, said Professor Gretchen Benedix, a planetary science researcher at Curtin University.

“It’s not totally out to lunch, these things happen. It’s more rare they happen within a lunar distance,” she said.

“If that were to hit the Earth, that would be bad. Something 100 metres across would leave a noticeable hole on the planet.”

The Chelyabinsk meteor, which exploded over Russia in 2013, was only about 20 metres in diameter.

Astronomers typically try to pick up asteroids long before they pass by Earth.

But this one was particularly difficult to see because it was coming toward the Earth from the direction of the sun, Professor Brown said.

From:  Impact Earth!

Inputs
Diameter = 328 feet
Asteroid type = dense rock
Angle = 45 degrees
Speed = 55,000 miles per hour
Water depth = 200 feet
Distance from impact = 50 miles

• The projectile begins to breakup at an altitude of 60200 meters = 198000 ft
• The projectile reaches the ground in a broken condition.  The mass of projectile strikes the surface at velocity 9.53 km/s = 5.92 miles/s
• The impact energy is 7.13 x 10^16 Joules = 1.7 x 10^1 MegaTons.
• The broken projectile fragments strike the ground in an ellipse of dimension 0.819 km by 0.579 km
• Energy before atmospheric entry: 4.9 x 10^17 Joules = 1.17 x 10^2 MegaTons TNT
• The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 6 x 10^3 years
• The Earth is not strongly disturbed by the impact and loses negligible mass.
• The impact does not make a noticeable change in the tilt of Earth’s axis (< 5 hundredths of a degree).
• The impact does not shift the Earth’s orbit noticeably.
• The crater opened in the water has a diameter of 2.17 km ( = 1.35 miles ).
• For the crater formed in the seafloor:
• Crater shape is normal in spite of atmospheric crushing; fragments are not significantly dispersed.
• Transient Crater Diameter: 1.12 km ( = 0.698 miles )
• Transient Crater Depth: 397 meters ( = 1300 feet )
• Final Crater Diameter: 1.4 km ( = 0.872 miles )
• Final Crater Depth: 299 meters ( = 980 feet )
• The crater formed is a simple crater.
• The floor of the crater is underlain by a lens of broken rock debris (breccia) with a maximum thickness of 139 meters ( = 454 feet ).
• At this impact velocity ( < 12 km/s), little shock melting of the target occurs.
• Most ejecta is blocked by Earth’s atmosphere.
• At this impact velocity ( < 15 km/s), little vaporization occurs; no fireball is created, therefore, there is no thermal radiation damage.
• The major seismic shaking will arrive approximately 16.1 seconds after impact.
• Richter Scale Magnitude:  5.2
• Mercalli Scale Intensity at a distance of 80.5 km:
• Felt quite noticeably by persons indoors, especially on upper floors of buildings.  Many people do not recognize it as an earthquake.  Standing motor cars may rock slightly.  Vibrations similar to the passing of a truck.
• Felt indoors by many, outdoors by few during the day.  At night, some awakened.  Dishes, windows, doors disturbed; walls make cracking sound.  Sensation like heavy truck striking building.  Standing motor cars rocked noticeably.
• The air blast will arrive approximately 4.07 minutes after impact.
• Peak Overpressure: 1980 Pa = 0.0198 bars = 0.28 psi
• Max wind velocity: 4.62 m/s = 10.3 mph
• Sound Intensity: 66 dB (Loud as heavy traffic)
• The impact-generated tsunami wave arrives approximately 55 minutes after impact.
• Tsunami wave amplitude is between: 82.2 cm ( = 32.4 inches) and 1.64 meters ( = 5.39 feet).