Just wanted to point out that the largest known asteroid to hit Earth was the
Vredefort impactor which struck Earth 2 billion years ago in what is today South Africa. It is thought to have been anywhere from 5 to 10 km in diameter and traveling at a rate of 20km/s (Mach 58). Now, using the calculator provided by Algaro, I got this result:
Distance from Impact: 20000.00 km ( = 12400.00 miles )
Projectile diameter: 5.00 km ( = 3.11 miles ) Projectile Density: 2000 kg/m3 Impact Velocity: 20.00 km per second ( = 12.40 miles per second ) Impact Angle: 45 degrees Target Density: 2500 kg/m3 Target Type: Sedimentary Rock
Energy before atmospheric entry:
2.62 x 1022 Joules = 6.25 x 106 MegaTons TNT The average interval between impacts of this size somewhere on Earth during the last 4 billion years is
1.9 x 107 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 hundreths of a degree). The impact does not shift the Earth's orbit noticeably.
Transient Crater Diameter:
34.8 km ( = 21.6 miles ) Transient Crater Depth:
12.3 km ( = 7.64 miles )
Final Crater Diameter:
55.5 km ( = 34.5 miles ) Final Crater Depth:
992 meters ( = 3250 feet ) The crater formed is a complex crater. The volume of the target melted or vaporized is
164 km3 = 39.4 miles3 Roughly half the melt remains in the crater, where its average thickness is
173 meters ( = 566 feet ).
The major seismic shaking will arrive approximately 1.11 hours after impact. Richter Scale Magnitude:
9.1 Mercalli Scale Intensity at a distance of 20000 km:
Nothing would be felt. However, seismic equipment may still detect the shaking.
^So with this, and with a
significant margin of error as I am not the best when it comes to calcs, we have
6.25 Teratons as an extreme low-end for the asteroid, which according to our
Attack Potency chart is
Small Country level.
Using the same calculator, if we threw Ceres, the largest object in the Asteroid Belt, toward Earth at the same rate and distance as the Vredefort impactor, we'd get hit with
45.6 Petatons of force, which would be
Continent level. Hypothetically, if Battra's asteroid were around the size of either Vredefort or Ceres then we should expect to see similar results.