The Chicxulub Impactor

Supposed dino killer 66 Ma
A CM or CR carbonaceous chondrite asteroid having an estimated diameter of 18.64 - 46.23 kilometers (11.6 - 28.7 mi), travelling between 12.6 - 40.7 km/sec, 45,360 - 146,520 km/hr, and delivering an estimated energy of 138 billion Hiroshima A-bombs (approximately 8.71×10^24 Joules).

Irrespective of the size or velocity of the impactor it appears to have been required to deliver an estimated energy of 138 billion Hiroshima A-bombs to create a crater 170 km wide. Within acceptable ranges, of course.
The velocites given above are the acceptable asteroid "range of velocities for bodies that cross Earth's orbit"[1]

The general perception with the public regarding the extinction of the dinosaurs is that they were wiped out by a meteorite impact. This theory has inarguably become the most famous and highly publicized cause for the disappearance of the species 65 million years ago. Its popularity has caused it to be universally accepted as the only viable theory to explain the disappearance of the dinosaurs.
https://hoopermuseum.carleton.ca/saleem/meteor.htm
More recent docs use 66 Ma.

Point of impact: The Chicxulub crater at the Yucatan Peninsula of Mexico.

In 1980, a team of researchers led by Nobel prize-winning physicist Luis Alvarez, his son, geologist Walter Alvarez, and chemists Frank Asaro and Helen Vaughn Michel discovered that sedimentary layers found all over the world at the Cretaceous–Paleogene boundary (K–Pg boundary, formerly called Cretaceous–Tertiary or K–T boundary) contain a concentration of iridium hundreds of times greater than normal. Iridium is extremely rare in the Earth's crust because it is very dense and has the affinity for iron that characterizes the siderophile elements (see Goldschmidt classification), and therefore most of it sank into the Earth's core while the earth was still molten. The Alvarez team suggested that an asteroid struck the earth at the time of the Cretaceous–Paleogene boundary.
https://carlsbadhistoricalsociety.com/Carlsbad%20Historical%20Society_files/AllanOKelly/alvarezhypothesis.pdf

Approximate location of the Chicxulub impact crater, in the Yucatan Peninsula in Mexico, near the town of Chicxulub.

Approximate location of the Chicxulub impact crater, in the Yucatan Peninsula in Mexico, near the town of Chicxulub.

Approximate location of the Chicxulub impact crater, in the Yucatan Peninsula in Mexico, near the town of Chicxulub.

"The Alvarezes along with Asaro and Michel published their seminal 1980 paper" “Extraterrestrial Cause for the Cretaceous-Tertiary Extinction” about "the demise of the dinosaurs" but gave no information about a crater. This changed with "the discovery in 1991 of the scene of the crime – the Chicxulub crater, a 180-kilometer-wide, 20-kilometer-deep impact crater off the northern coast of the Yucatan peninsula in the Gulf of Mexico that is buried beneath a kilometer of Tertiary carbonates. The discovery of this impact site answered critics who’d been demanding to know: If an asteroid impact killed the dinosaurs, where’s the crater?"
https://newscenter.lbl.gov/2010/03/09/alvarez-theory-on-dinosaur/

Background

I was recently checking some pages and found that some of the quotes I had used had been updated / changed etc on their referenced pages. These mainly had to do with the Chicxulub impactor and the devastation it caused impacting the Earth. For example, one quote gave:

The Chicxulub impactor had an estimated diameter of 11-81 kilometers (6.8-50.3 mi), and delivered an estimated energy of 21-921 billion Hiroshima A-bombs (between 1.3x10²⁴ and 5.8x10²⁵ joules, or 1.3-58 yottajoules). For comparison, this is ~100 million times the energy released by the Tsar Bomba, a thermonuclear device ("H-bomb") that remains the most powerful human-made explosive ever detonated, which released 210 petajoules (2.1x10¹⁷ joules, or 50 megatons TNT).
http://web.archive.org/web/20211228051109/https://en.wikipedia.org/wiki/Chicxulub_crater

Checking in June 2022 I found this had been replaced by:

It was formed when a large asteroid, about 10 kilometers (6.2 miles) in diameter, struck Earth. The impactor's velocity was estimated at 20 kilometers per second. The kinetic energy of the impact was estimated at 100 teratons of TNT, more than 4.5 billion times the energy of the atomic bomb dropped on Hiroshima, Japan.
https://en.wikipedia.org/wiki/Chicxulub_crater

I found the original source for the old quote so I could still use it but time had moved on and new studies were suggesting a diameter of 10 km and destructive force of approximately 4.5 billion A. bombs [or more. How much more?]. I chased this new quote to its source [as far as I could go but couldn't check it all] and found someone else talking about it:

Even before the asteroid hit, it was primed for decimation, colliding with Earth at the most destructive angle, according to a 2020 study published in Nature Communications. The asteroid was about 7.5 miles (12 kilometers) in diameter and was traveling about 27,000 mph (43,000 km/h) when it created a 124-mile-wide (200 km) scar on the planet's surface, said Sean Gulick, a research professor at the University of Texas Institute for Geophysics, who led the study. More importantly, the asteroid struck the planet at about 60 degrees above the horizon. This angle was particularly destructive because it allowed the asteroid's impact to eject a large amount of dust and aerosols into the atmosphere.
https://www.livescience.com/dinosaur-killing-asteroid-struck-earth

But there are some simple discrepancies here. 43,000 km/hr translates to approximately 11.94 km/sec, not 20 as suggested. Digging a bit deeper I found the new quote was quoting a study:
Collins, G. S.; Patel, N.; Davison, T. M.; Rae, A. S. P.; Morgan, J. V.; Gulick, S. P. S. (May 26, 2020). "A steeply-inclined trajectory for the Chicxulub impact". Nature Communications. 11 (1): 1480.
which when you open up is really supporting 60 degree trajectory simulations with a 17 km wide impactor, velocities 12 and 20 km/s used.

"The impact simulations shown in Figs. 2 and 3 employ an impact speed of 12 km/s, only slightly larger than the minimum possible speed—Earth’s escape velocity of 11.2 km/s. While these results are likely to be representative of the ~25% of all impacts that occur at speeds below 15 km/s, we also conducted another suite of simulations with a more probable impact speed of 20 km/s (close to Earth’s mean and median asteroid impact speed) ...

In summary, our numerical simulations of oblique Chicxulubscale impacts appear to be most consistent with the internal structure of the Chicxulub crater for a steeply inclined impact angle of 45–60° to the horizontal."
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7251121/pdf/41467_2020_Article_15269.pdf

Note this paper really had more to do with the impact angle and not the velocity or size of the impactor. Though looking at the impact simulations they have used two impactor sizes: 17 km and 21 km diameters.

And bear in mind that some older quotes I have used [and still use] give higher velocities:

A comet or an asteroid—we aren't sure which—collided with the Earth, hitting what is now the Yucatan Peninsula of Mexico. It was about six miles (ten kilometers) wide, or about the size of Mount Everest. It was probably moving at a speed of around 67,000 miles per hour (108,000 kilometers per hour), more than a hundred times faster than a jet airliner. When it slammed into our planet, it hit with the force of over 100 trillion tons of TNT, somewhere in the vicinity of a billion nuclear bombs' worth of energy. It plowed some twenty-five miles (forty kilometers) through the crust and into the mantle, leaving a crater that was over 100 miles (160 kilometers) wide. p.315.
The RISE and FALL of the DINOSAURS
A New History of Their Lost World, STEVE BRUSATTE. 2018.

This comet is 10 kilometres in diameter, taller than Mt Everest or larger than the Martian moon Deimos. This harbinger of destruction is travelling at a speed of more than 100000 kilometres per hour and its energy of motion has the destructive force of 100 million hydrogen bombs. p.163.
Flying Dinosaurs: How fearsome reptiles became birds, John Pickrell, 2014.

And looking at the new quotes I am left with some questions:

The diameter of the impactor: 10 km, 12 km, 17 km, or 21 km?

with velocity: 43,000 km/hr [approx 11.94 km/sec], 43,200 km/hr [12 km/sec], or 72,000 km/hr [20 km/sec]?

So I decided I would have a shot at this and see if there was any way to resolve this puzzle.

The solution

I looked on the internet to see if anyone had made any tables of crater size given meteor diameters. Maybe someone has but I found something better. A site where you could enter the velocity and diameter of a meteor and it would calculate the size of the crater. It also needed data for the graze angle [degrees from the horizontal] and density of the meteor.
Asteroid Impact Crater Calculator.[2]

The new quote gave an angle of 60°. The following gives some more information about finding the angle:

Supercomputer simulates the impact of the asteroid that wiped out dinosaurs
A team of researchers has managed to run 3D models from the moment that the comet hit the surface of the Earth, until the 110-mile wide crater was fully formed.

a team of researchers equipped with a supercomputer has managed to simulate the entire event, shedding light on the reasons that the impact led to a mass extinction of life.

The simulations were carried out by scientists at Imperial College in London, using high performance computing (HPC) facilities by Hewlett Packard Enterprise.

Various impact angles and speeds were considered, and 3D simulations for each were fed into the supercomputer. These simulations were then compared with the geophysical features that have been observed in the 110-mile wide Chicxulub crater, located in Mexico's Yucatán Peninsula, where the impact happened.

The simulations that turned out to be the most consistent with the structure of the Chicxulub crater showed an impact angle of about 60 degrees. Such a strike had the strength of about ten billion Hiroshima bombs, and this particular angle meant that rocks and sediments were ejected almost symmetrically.
https://www.zdnet.com/article/supercomputer-simulates-the-impact-of-the-asteroid-that-wiped-out-dinosaurs/

So I could use 60° as the graze angle. What about the density? The two guys from Mexico who did the paper that gave a maximum impact energy of 921 billion Hiroshima bombs had this problem. They didn't know the exact density so used a few examples:

Because the interval of time that separates us from the formation of Chicxulub is so large, the evidence that could help to reconstruct impactor features are few. The most obvious is the diameter of the crater, which is between 180 and 200 km (Schulte et al., 2010). With these extreme values and equations (2.1.2), (2.2.2), (2.3.2), (2.4.10) we can estimate the energy of the impactor.

We considered the density of the projectile as 1650 kg m^-3 for comets (Greenberg, 1998), 3400 kg m^-3 for stony asteroids (Wilkison and Robinson, 2000), and 8000 kg m^-3 for iron asteroids (Hills and Goda, 1993). ... Steel (1998) obtained an estimation of the range of velocities for bodies that cross Earth's orbit. For asteroids the interval is between 12.6 km s^-1 and 40.7 km s^-1. This result is based on measurements of the velocities of the asteroids that cross Earth's orbit.

The range for comets is between 16 km s^-1 and 73 km s^-1.

we concluded that the most probable impactor was a fast asteroid or a long-period comet with energy between 1.3x10²⁴ J and 5.8x10²⁵ J, mass between 1.0x10¹⁵ kg and 4.6x10¹⁷ kg, and diameter between 10.6 km and 80.9 km.
Assessments of the energy, mass and size of the Chicxulub Impactor
Hector Javier Durand-Manterola and Guadalupe Cordero-Tercero

This was a very good start and the range approach these two guys took was one I was going to follow. They didn't know the exact density of the asteroid but a more recent study does give some hints:

careful consideration of the geochemical evidence strongly favors a CM or CR carbonaceous chondrite, and rules out a cometary impactor.

the impactor must be a CM or CR chondrite, and this makes asteroids plausible
Desch et al.
"The Chicxulub impactor: comet or asteroid?"

And on a page about meteorite densities I found the following:

All densities are measured in grams per cubic centimetre. (g/cm³)

Carbonaceous Chondrites:
CI 2.11
CM 2.12 (± 0.26)
CR 3.1
http://meteorites.com.au/odds&ends/density.html

Before continuing on, one old page gave the kinetic energy range from the two guys from Mexico as "an estimated energy of 21-921 billion Hiroshima A-bombs" but this was not stated in their paper. But it can be approximated by using the following:

The following is a summary of the features of the atomic bomb (“Little Boy”) dropped on Hiroshima. It has been estimated that it was equivalent to 16 KT of TNT (trinitrotoluene, explosive). Only about 860 g of the 70 kg of U-235 contained in the bomb was thought to have exploded. The energy released was 6.3 × 10¹³ J (63 TJ) (Little Boy, Wikipedia; Los Alamos Report (1985)).
https://www.researchgate.net/publication/299686845_Devastation_Caused_by_the_Atomic_Bombs_Hiroshima_and_Nagasaki

And using their estimated range of "energy between 1.3x10²⁴ J and 5.8x10²⁵ J" we obtain approximately 20.6 to 920.6 or 21 to 921 billion Hiroshima A-bombs as stated above.

Now looking at the online software I need to enter the asteroid diameter, density, velocity, and graze angle. We have two possible densities, and a graze angle. The two guys from Mexico suggest an asteroid velocity range of "12.6 km s^-1 and 40.7 km s^-1." We would simply use the end points giving us a range. So we have two densities and two velocities. Then there will be four calculations to do. We don't know the size of the asteroid but we can put in varying amounts until we reach a desired crater size.

So we need a crater size to work to. The two guys from Mexico used a standard value, "the diameter of the crater, which is between 180 and 200 km." But there appears to be no clear unanimity on the crater diameter with values suggested of 150 km, 160 km, 170 km, 180 km, 200 km and even 260 km! A gravity study giving 170 km gets mentioned a few times and an earlier paper I found on this gives:

CHICXULUB CRATER SIZE AND STRUCTURE AS REVEALED BY HORIZONTAL BOUGUER GRAVITY GRADIENTS AND CENOTE DISTRIBUTION; A.R. Hildebrand, et at.
The size of the Chicxulub crater, Yucatan, Mexico is currently in dispute with diameter estimates ranging from 170km upwards of 300 km ...
No concentric gradient features were found at distances >85 km radius. ...
The cenotes' distribution does not reveal any concentric structure at radii >85 km; ...
This terrace width satisfies the relationship defined by lunar craters for a crater of 170 km diameter
https://www.lpi.usra.edu/meetings/lpsc1995/pdf/1302.pdf

This document gives a footnote on each page stating "Lunar and Planetary Institute Provided by the NASA Astrophysics Data System" which does suggest this document carries a reasonable amount of weight on this topic. That said, I am going to use their suggested crater diameter value of 170 km.

And though this may be debatable it should still be a reasonable estimate and a good place to start.

Also the software outputs two diameter values: actual and apparent. Confusing the matter is the software outputting the apparent diameter as larger where some documentation suggests it should be smaller. No matter, I am simply going to use 170 km as the actual diameter and expect outputs for the apparent diameter to be 180 to 200 km or larger. This should make some sort of sense with the majority of quotes stating a crater size of 180 to 200 km wide.

OK that's about it so how did the calculations turn out?

For a 170 km wide target crater value and going to closest round figures I obtained:

CM 2.12 g/cc velocity 12.6 km/s.
Gives diameter 46.23 km, Mass 1.1x10^17 kg, KE 8.71x10^24 Joules, 138 billion Hiro.B
CM 2.12 g/cc and 40.7 km/sec.
Gives diameter 21.16 km, Mass 1.05x10^16 kg, KE 8.71x10^24 Joules, 138 billion Hiro.B
CR 3.1 g/cc and 12.6 km/sec.
Gives diameter 40.73 km, Mass 1.1x10^17 kg, KE 8.71x10^24 Joules, 138 billion Hiro.B
CR 3.1 g/cc and 40.7 km/sec.
Gives diameter 18.64 km, Mass 1.05x10^16 kg, KE 8.71x10^24 Joules, 138 billion Hiro.B

And calculating the velocities to km/hr:
12.6 km/sec = 45,360 km/hr
40.7 km/sec = 146,520 km/hr

At first I was puzzled about this. Every example gave the same result. Changing the density for the different chondrites and the velocities all yielded the same amount of energy. Approximately the equivalent of 138 billion Hiroshima bombs. And then it struck me. The impactor size and masses were simply being adjusted to give the same amount of energy. So it must be the energy required to create a crater 170 km wide!! Which simply is a constant! The equivalent of 138 billion Hiroshima A bombs. That's it!!

From these results we could write a simple statement:

The Chicxulub Impactor
A CM or CR carbonaceous chondrite asteroid having an estimated diameter of 18.64 - 46.23 kilometers (11.6-28.7 mi), travelling between 12.6 - 40.7 km/sec, 45,360 - 146,520 km/hr, and delivering an estimated energy of 138 billion Hiroshima A-bombs (approximately 8.71×10^24 Joules).

And a simple table could be constructed as follows...

Supposed dino killer
A CM or CR carbonaceous chondrite asteroid

So that's it. You may not agree with these results but this is my spin on it. And you can read what I really think about a lot of this stuff on some of my other pages.

REFERENCES

Page design/construction Stephen Buckley 2022.