How big was Ancalagon?

[Raynor]

Stand back, I'm gonna try science!
http://impact.ese.ic.ac.uk/cgi-bin/c...s=1&tdens=2750

Distance from Impact: 500.00 meters ( = 1640.00 feet ) Projectile diameter: 30.00 meters ( = 98.40 feet ) Projectile Density: 1500 kg/m3 Impact Velocity: 100.00 km per second ( = 62.10 miles per second ) (Your chosen velocity is higher than the maximum for an object orbiting the sun)Impact Angle: 45 degrees Target Density: 2750 kg/m3 Target Type: Crystalline Rock

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.

Blank template: http://impact.ese.ic.ac.uk/ImpactEffects/

[Nerwen]

Ah, what fun. Let's plug some different numbers into it.

Distance from Impact: 1000.00 meters ( = 3280.00 feet )
Projectile diameter: 300.00 meters ( = 984.00 feet )
Projectile Density: 1500 kg/m3
Impact Velocity: 50.00 km per second ( = 31.10 miles per second )
Impact Angle: 90 degrees
Target Density: 2500 kg/m3
Target Type: Sedimentary Rock

The projectile begins to breakup at an altitude of 89700 meters = 294000 ft
The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 46.3 km/s = 28.8 miles/s
The impact energy is 2.27 x 1019 Joules = 5.43 x 103MegaTons.
The broken projectile fragments strike the ground in an ellipse of dimension 0.655 km by 0.655 km

Crater shape is normal in spite of atmospheric crushing; fragments are not significantly dispersed.

Transient Crater Diameter: 5.73 km ( = 3.56 miles )
Transient Crater Depth: 2.03 km ( = 1.26 miles )

Final Crater Diameter: 7.23 km ( = 4.49 miles )
Final Crater Depth: 537 meters ( = 1760 feet )
The crater formed is a complex crater.
The volume of the target melted or vaporized is 0.202 km3 = 0.0485 miles3
Roughly half the melt remains in the crater, where its average thickness is 7.85 meters ( = 25.8 feet ).