Season 17, Episode 46: How Likely Are You to Get Hit By a Meteorite?

Hey StarTalkians! Episode 46 of season 17 had Neil and Chuck tackling some Cosmic Queries, including this challenging question about meteorite impacts:

Cosmic Queries – Planet 9 - StarTalk Radio

(From 39:30)

The question mentioned the unique story of Ann Hodges, one of the only recorded cases of someone getting hit. Neil avoided estimating the odds without doing some calculations, but what type of numbers have people come up with? How likely is it?

The Story of Ann Hodges

Ann Hodges was taking an afternoon nap on her couch on November 30th, 1954 when a fragment of a meteorite crashed through her roof, smashed into her radio and struck her in the thigh. The meteorite was a stony, chondrite type and weighed 3.86 kg (8.5 lb), and left a serious bruise (see images). But other than some (very understandable) anxiety, she was OK.

But as the question pointed out, it seems kind of weird that this type of thing doesn’t happen more.

What is the “Meteorite Flux” of the Earth?

The question really revolves around what’s called the meteorite “flux” of the Earth – that is, the rate at which meteorites hit the Earth.

A 1996 paper offers a couple of good estimates for meteorites weighing over 10 g. The paper’s estimate is around 95 per million square kilometres per year, but an earlier estimate puts it at 83. For bigger meteorites, like the one that hit Ann, it’s about 8.7 per million square km or even less.

How Likely Are You to Get Hit?

This is spread evenly over the surface of the Earth, but – as Neil points out – the population is not. In fact, 95% of the population occupies just 10% of the land area.

So including anything above 10 g, about 1,236 meteorites fall on this more populated area per year. For meteorites above 1 kg, it’s more like 130 per year.

Even counting smaller meteorites, this makes it about a 1 in 12,000 chance that there will be an impact in any square km in one year. And about 530 people will occupy that space. Even if every single strike hit someone, that puts the odds at less than 1 in 6 million for each person per year. And even that is an overestimate, since most would still miss.

Other estimates are a little higher, with astronomer Dr. Clark Chapman putting it at about 1 in 1.6 million over a lifetime.