> Spanky at 99% the speed of light...

Got a Claude account for a project.  Got some extra credits to be stupid with it:


Input: How much energy would a body weighing 266 kg and having a density of 0.95 gram per centimeter cubed, traveling at 99% the speed of light through outer space, create if hit the earth?

Claude:

The energy released on impact would be the object's relativistic kinetic energy, which works out to roughly 1.46 × 10²⁰ joules — about 35 gigatons of TNT.
Here's the calculation.
At 99% the speed of light you can't use the classic ½mv² formula; you need the relativistic version, because the kinetic energy blows up as you approach c. The formula is:
KE = (γ − 1)mc²
where γ (the Lorentz factor) is:
γ = 1 / √(1 − v²/c²)
Plugging in v = 0.99c:

v²/c² = 0.9801
1 − 0.9801 = 0.0199
√0.0199 ≈ 0.14107
γ = 1 / 0.14107 ≈ 7.089

So the object carries about 7× its rest energy in motion alone. Now:

mc² = 266 kg × (2.998 × 10⁸ m/s)² ≈ 2.39 × 10¹⁹ J
KE = (7.089 − 1) × 2.39 × 10¹⁹ ≈ 6.089 × 2.39 × 10¹⁹ ≈ 1.46 × 10²⁰ J


To put that number in perspective:

≈ 34,800 megatons of TNT
≈ 700 Tsar Bombas (the largest nuke ever detonated, ~50 Mt)
≈ 2 million Hiroshima bombs

It would carve out a substantial crater and devastate a wide region, though it's still tiny next to the dinosaur-killing Chicxulub impact (~100 million megatons).
One note on the density: it doesn't actually enter the energy calculation, since you gave the mass directly. What it does tell you is the object's size. At 0.95 g/cm³ (just under water, so something icy/cometary), 266 kg occupies about 0.28 m³ — a sphere roughly 80 cm across. So this is a small, fridge-sized chunk of ice, and essentially all of its destructive power comes from that staggering velocity, not its size.


Input:  Estimate the number of killed, wounded, and total dollar value of property damage if this impact hit at this longitude and latitude:   41.99313153907353, -88.18676249640674


Claude

Quick framing: this is a disaster-modeling exercise, the same kind of thing asteroid-impact and nuclear-effects simulators do. The numbers below are order-of-magnitude estimates with wide error bars, not predictions.
Where ground zero is
Those coordinates land in Bartlett, Illinois — a village straddling Cook, DuPage, and Kane counties, about 53 km (33 mi) west-northwest of downtown Chicago, right in the heart of the densely populated western suburbs. So this isn't a remote impact; it's effectively in the middle of Chicagoland (metro population ~9.4 million in the MSA, ~9.8 million in the broader CSA).
A caveat that changes the physics
Your object isn't a normal asteroid. A slow asteroid delivering 35 gigatons would be a 1.5-km rock punching a clean crater. Yours is an 80-cm, fridge-sized chunk of ice moving at 0.99c — it crosses the entire atmosphere in about a third of a millisecond. Rather than excavating a tidy crater, it would shred via relativistic nuclear interactions, dumping its energy as a fireball + air-blast + an intense burst of gamma rays and particle showers at and near the surface. For casualty purposes, the right mental model is a ~35-gigaton explosion centered on Bartlett, roughly comparable in total energy to a ~1.5 km asteroid strike — a regional, sub-global catastrophe.
Approximate damage zones
Radii are uncertain for two reasons: relativistic energy-deposition profiles aren't well characterized, and standard cube-root blast scaling overestimates lateral reach at multi-gigaton yields (the atmosphere vents much of the energy straight up). With that said:
ZoneRadius from BartlettEffectTotal destruction~0–40 kmVaporization near center; essentially all structures destroyed; ~100% fatalSevere~40–90 kmMost buildings collapsed, mass fires, severe burns; ~30–90% fatalModerate~90–200 kmDamaged/collapsed structures, flying glass, thermal-ignited fires; injuries widespreadLight~200–300+ kmBroken windows, minor injuries; flash and shockwave felt
Because Bartlett sits on the western edge of the metro, the bulk of Chicagoland's population lies to the east within ~50–100 km — squarely inside the total-destruction and severe zones. The 40 km circle alone engulfs the western and central suburbs and the western edge of the city; the 90 km circle swallows the entire city, the lakefront, and into northwest Indiana.
Estimated human toll
Mapping the population against those zones:

Killed: roughly 4–6 million. The inner ~40 km holds several million people at near-total lethality; the 40–90 km band adds the dense city core and inner suburbs. (If blast coupling is on the conservative end, this could be closer to 2–3 million — still catastrophic.)
Wounded: roughly 3–5 million — burns, blast trauma, crush injuries, radiation exposure — overwhelming every hospital in the region many times over.
Total affected: essentially the entire metro (~9–10 million), plus lighter effects reaching Rockford, Milwaukee (~150 km), and into southern Wisconsin and northwest Indiana.

Property and economic damage
The metro's residential housing stock alone is worth about $1.2 trillion (Zillow, 2025), and most of it sits inside the severe zone. Adding commercial real estate, O'Hare and Midway, the rail infrastructure (Chicago is the largest rail interchange in North America), utilities, business capital, vehicles, and contents:

Direct physical destruction: ~$2–4 trillion.
Total economic loss: ~$5–10+ trillion, once you include displacement of ~9 million people, the loss of one of the country's largest economic hubs, and the national supply-chain shock from knocking out the central US logistics nexus.

The bigger picture
This would be among the worst single-event disasters in human history — well beyond any natural disaster on record, in the same league as a regional nuclear exchange. Secondary effects pile on: a local earthquake on the order of magnitude 5–6, a possible wide-area electronics/EMP-style disruption from the particle and gamma burst, fallout-like contamination from irradiated debris, and a firestorm across the urbanized area. It's still far short of the dinosaur-killer (Chicxulub was ~3 million times more energetic), so it wouldn't threaten civilization globally — but for the Chicago region, it would be a near-total loss.