The speed and mass of this asteroid

Background:

In the world of Krynn (Dragonlance) there was this worldwide catastrophe, the Cataclysm.

What happened: Gods became angery to a single person, so they threw an asteroid at him, obliterating half the known world in the process.

Information

I want to make a campaign where the gods are revealed to be beings with way higher technological levels, so in order to make this setting change proper, I should really figure out the mass and the speed of that meteor.

• I calculated the crater to be approx 637,42 miles in diameter.
• Depth is unknown.

Question

What would be the real side-effects of this level of destruction? How big would the asteroid have to be, to create this large crater, that gets filled in by the ocean later?

• Comments are not for extended discussion; this conversation has been moved to chat. – JDługosz May 15 '17 at 22:24

Assuming we're asking for a 637 mile wide (1000 km) crater, I played around with an Asteroid Impact Calculator and found that a 35 km asteroid would be required creating a final crater (ie. after everything stops collapsing) 1.5 miles deep. I gave it every advantage I could: made of iron, almost impossibly high impact velocity of 72km/s, 90° impact angle.

Mercury probably received a hit like this that formed the Caloris Planitia; a 1500 km wide basin ringed by mountains 2 km high which threw material for another 1000 km.

The problem is such an asteroid would be many, many, many times more massive than the asteroid which likely caused the Cretaceous–Tertiary (K–T) extinction 66 million years ago. That left a 150 km crater and wiped out 75% of all species on Earth. This asteroid is much bigger. Much, much, much, much bigger!

Mass and energy of an asteroid is proportional to its density and volume. Volume increases with the cube of the diameter. The K-T asteroid had a volume of roughly $525~\text{km}^3$. Ours has a volume of $22\,500~\text{km}^3$ with a corresponding increase in mass and energy. The K-T asteroid released about $5 \times 10^{23}~\text{J}$, this asteroid would release 1,000 times more: $5 \times 10^{26}~\text{J}$.

That's the total energy the Earth receives from the Sun in 100 years. It's like being smacked by 10 solar flares all at once. There's no getting around it, if you want to create a 1000 km crater with an impact it's going to take a lot of energy. Too much energy to have a meaningful fantasy setting afterward... or any setting at all.

This is the sort of asteroid the Earth hasn't seen since the Late Heavy Bombardment during the planet's formation. This is an asteroid nobody walks away from. Civilization isn't just harmed, everything is made extinct and the surface of the planet is converted into a molten hell at the speed of sound.

There lies the problem with trying to put a scientific backing to sci-fi & fantasy worlds: the authors generally don't know or don't care about the physics involved and get the scale wrong (and then there's the very questionable geography of that map). If you want to make your campaign scientific, everything is dead and the surface is uninhabitable for millennia.

Stick with magic.

• Wrapping your scientific notation in \$just to get the exponent also messes up the letters. Try “ 5 × 10<sup>23</sup> J ” for example. – JDługosz Mar 24 '17 at 6:09 • @JDługosz Thanks, just learning MathJax. – Schwern Mar 24 '17 at 6:46 • Look for some old posts on Worldbuilding Meta about it. Here's one – JDługosz Mar 24 '17 at 6:56 • I think I fixed all of your remaining Mathjax formatting issues. For a really in-depth guide to Mathjax and$\LaTeX\$, try MathJax basic tutorial and quick reference on Mathematics Meta. – a CVn May 15 '17 at 20:34

Following Schwern answer, and looking at your map, what you actually want is an asteroid impacting in an artic zone. It doesn't kill anybody - the gods are way worse than your kingpriest if they kill several million innocent people just to send a warning - but it sends an earthquake that's felt all over the globe, then a not sudden, but definitely quick raising seawater level which floods part of your original continent until it resembles your second picture.

Not many deads, if any, but millions of refugees and a totally bankrupted empire as a result. Now, that's a severe amonestation.

• Wait, arctic zone? The similarities between Dragonlance and Neon Genesis Evangelion are getting more suspicious. But yeah, the gods were way worse (or stupid), even in the setting. – Mephistopheles Mar 24 '17 at 13:49
• Sea level rise is a good idea, but the maps don't work. There were mountains where the new sea is. The central mountain range ends up somehow larger. After the impact there's now a polar ice cap which would lower sea levels. You'll have to alter the maps some to make it work. Istar could be in a situation like the Salton Sea, lowlands separated from the ocean by coastal highlands. A much smaller asteroid could have carved a channel connecting it to the sea. But it doesn't explain all the other changes. More asteroids? – Schwern Mar 24 '17 at 20:38