An interstellar object exploded over Earth in 2014, declassified government data reveal

Live Science ^ | Brandon Specktor

[Alvin Diogenes]

"Did anybody see this rock, or take a picture of it, before it blew up? If not, how do we know it was only 1.5 feet across?"

It looks like they went through the following steps:

1. Compute an approximate mass based on the impact energy and the impact speed.
2. Take that approximate mass, and compute the volume using an educated guess for the density of the object (volume = mass / density).
3. Solve for the radius R: assuming the object was approximately spherical, its volume V can be written as 4π R^3 / 3, so R is the cube root of 3V / 4π.

Here's the relevant quote from the ArXiv preprint, Section 3.2 Size Distribution:

"Given the impact speed of the meteor, ∼ 44.8 km s⁻¹, and the total impact energy, 4.6 × 10¹⁸ ergs, the meteor mass was approximately 4.6 × 10⁵ g. Assuming bulk density values of 1.7 g/cm³ and 0.9 g/cm³ for Type II and Type IIIa objects respectively, we obtain a radius, R, of 0.4m - 0.5m for a spherical geometry (Ceplecha 1988; Palotai et al. 2018)."

This appears to be just an approximation to give an idea of the size, but it's probably about right. I don't think they give an error estimate.

[cgbg]

This is a hopeless spoiler alert but I will say the words anyway:

“The Expanse”

[Kevmo]

Nope. Not that story arc. But I did like that one.

[Tallguy]

I’m betting some tribesmen has a head hanging inside his hut that he didn’t need to shrink.