Nothing much happens to the world. Local destruction is immense, but it wouldn't be anything like an asteroid or comet impact. Relative velocity here is the key. If it would crash on Siberia or Canada, it would cause a lot of windows to break, maybe couple thousand reindeers and bears would snuff it, but that's about it.
Remember, we're talking about an object that is, at the beginning of the scenario, orbiting Earth. That means it has roughly the same velocity as Earth does; at maximum it's velocity relative to surface would be 11.2 km/s at the time of impact which is not exactly fast when you compare it to objects that are orbiting Sun, like asteroids and comets. Very likely the velocity would be significantly smaller, something like seven or eight kilometres per hour would not sound out of place.
Maximum velocity for objects that orbit the Sun is about 72 km/s, for comparision, and typical comet impact velocities are around 50 km/s.
At impact velocities below 15 km/s there is no fireball, the object just plummets to the ground, so no thermal damage. Most damage is caused by seismic vibrations and air blast. If it were to hit an ocean, it would create a tsunami, which would cause more destruction on coastlines, but it wouldn't be the end of world as we know it (except by revealing Shivan existence to the world).
University of Arizona has a handy tool for occasions such as this:
Impact effect calculatorEstimating the mass of a Sathanas is difficult. I ended up using density of water (1000 kg m^-3) and diameter of three kilometres. Changing the density to iron did not significantly change the outcome. The effects of impact at maximum velocity of 11 km/h were as follows:
Your Inputs:
Distance from Impact: 500.00 km = 310.50 miles
Projectile Diameter: 3000.00 m = 9840.00 ft = 1.86 miles
Projectile Density: 1000 kg/m3
Impact Velocity: 11.20 km/s = 6.96 miles/s
Impact Angle: 45 degrees
Target Density: 2500 kg/m3
Target Type: Sedimentary Rock
Energy:
Energy before atmospheric entry: 8.87 x 1020 Joules = 2.12 x 105 MegaTons TNT
The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 1.4 x 106years
Major Global Changes:
The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the Earth's rotation period or the tilt of its axis.
The impact does not shift the Earth's orbit noticeably.
Crater Dimensions:
What does this mean?
Transient Crater Diameter: 14.3 km = 8.91 miles
Transient Crater Depth: 5.07 km = 3.15 miles
Final Crater Diameter: 20.4 km = 12.7 miles
Final Crater Depth: 0.733 km = 0.456 miles
The crater formed is a complex crater.
At this impact velocity ( < 12 km/s), little shock melting of the target occurs.
Thermal Radiation:
What does this mean?
At this impact velocity ( < 15 km/s), little vaporization occurs; no fireball is created, therefore, there is no thermal radiation damage.
Seismic Effects:
What does this mean?
The major seismic shaking will arrive at approximately 100 seconds.
Richter Scale Magnitude: 8.2
Mercalli Scale Intensity at a distance of 500 km:
IV. 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.
V. Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.
Ejecta:
What does this mean?
The ejecta will arrive approximately 334 seconds after the impact.
At your position the ejecta arrives in scattered fragments
Average Ejecta Thickness: 3.03 mm = 0.119 inches
Mean Fragment Diameter: 1.85 mm = 0.0728 inches
Air Blast:
What does this mean?
The air blast will arrive at approximately 1520 seconds.
Peak Overpressure: 11300 Pa = 0.113 bars = 1.6 psi
Max wind velocity: 25.4 m/s = 56.9 mph
Sound Intensity: 81 dB (Loud as heavy traffic)
Damage Description:
Glass windows will shatter.
By comparision, here are results using iron as estimated density:
Your Inputs:
Distance from Impact: 500.00 km = 310.50 miles
Projectile Diameter: 3000.00 m = 9840.00 ft = 1.86 miles
Projectile Density: 8000 kg/m3
Impact Velocity: 11.20 km/s = 6.96 miles/s
Impact Angle: 45 degrees
Target Density: 2500 kg/m3
Target Type: Sedimentary Rock
Energy:
Energy before atmospheric entry: 7.09 x 1021 Joules = 1.69 x 106 MegaTons TNT
The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 6.9 x 106years
Major Global Changes:
The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the Earth's rotation period or the tilt of its axis.
The impact does not shift the Earth's orbit noticeably.
Crater Dimensions:
What does this mean?
Transient Crater Diameter: 28.8 km = 17.9 miles
Transient Crater Depth: 10.2 km = 6.32 miles
Final Crater Diameter: 44.8 km = 27.8 miles
Final Crater Depth: 0.929 km = 0.577 miles
The crater formed is a complex crater.
At this impact velocity ( < 12 km/s), little shock melting of the target occurs.
Thermal Radiation:
What does this mean?
At this impact velocity ( < 15 km/s), little vaporization occurs; no fireball is created, therefore, there is no thermal radiation damage.
Seismic Effects:
What does this mean?
The major seismic shaking will arrive at approximately 100 seconds.
Richter Scale Magnitude: 8.8
Mercalli Scale Intensity at a distance of 500 km:
VI. Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.
VII. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.
Ejecta:
What does this mean?
The ejecta will arrive approximately 334 seconds after the impact.
Average Ejecta Thickness: 4.89 cm = 1.92 inches
Mean Fragment Diameter: 4.15 mm = 0.163 inches
Air Blast:
What does this mean?
The air blast will arrive at approximately 1520 seconds.
Peak Overpressure: 37000 Pa = 0.37 bars = 5.26 psi
Max wind velocity: 76 m/s = 170 mph
Sound Intensity: 91 dB (May cause ear pain)
Damage Description:
Wood frame buildings will almost completely collapse.
Glass windows will shatter.
Up to 90 percent of trees blown down; remainder stripped of branches and leaves.
In pretty much all cases, damage is limited to radius of a thousand kilometres or so. Even in the case of iron spaceship, which is somewhat implausible but who knows what Shivans build their space ships of...
By the way here's a more interesting question; how much damage did Coruscant suffer when more than half of the Invisible Hand didn't crash on the implausibly well placed runway?
No one even mentions it since it separates from the forward section of the ship. It must've crushed several thousands of beings to death, yet no one even seems to spare a thought to what sort of destruction it would cause.
