More or Less: Behind the Stats
Episode: What are the chances of an asteroid hitting earth in 2032?
Host: Tim Harford (BBC Radio 4)
Date: March 22, 2025
Overview
This episode delves into the recent media storm around asteroid 2024 YR4, discovered in December 2024, and its potential to strike Earth in 2032. Host Tim Harford and NASA navigation engineer Davide Farnocchia break down the numbers, clarify why early predictions created alarm, and set the actual risk in scientific context—all while debunking fears stoked by sensational headlines.
Key Discussion Points & Insights
1. Discovery of Asteroid 2024 YR4 & Media Frenzy
- [01:38] Tim Harford recounts how astronomers in Chile discovered a new asteroid (2024 YR4), sparking wild predictions in the media about its potential to hit Earth and the likely devastation.
- Social media amplified the panic, asking if the asteroid could destroy entire cities or countries.
2. Initial Risk Assessment & Escalating Probabilities
- [02:30] Tim reveals the initial odds:
“The initial finding was a 1% likelihood of hitting Earth... shortly after discovery, this 1% likelihood was upgraded to 3%.”
- Only one recent asteroid approached this risk level; it failed to impact, as will a prominent near-Earth pass in 2029.
3. The Role of Asteroids in Earth’s History
- Recaps real asteroid impacts: Chelyabinsk (2013) and Tunguska (1908), both in Russia.
- Emphasizes how asteroid collisions have occasionally been catastrophic on a planetary scale, but most are far less dramatic.
4. Understanding Asteroids and Space Debris
- [03:41] Davide Farnocchia introduces his role:
“My name is Davide Farnocchia. I work as a navigation engineer at NASA's Jet Propulsion Laboratory and I track asteroids and comets for my job.”
- [04:38] On how much material actually reaches Earth:
“Space is mostly empty, but there is material. And Earth is reached by about 100 tons of interplanetary material pretty much any given day. ... Most of that is dust and so we don't even notice.”
- [04:59] Asteroids are described as leftovers from planet formation, mainly orbiting between Mars and Jupiter due to Jupiter’s gravity blocking a new planet from forming there.
5. How Asteroids Change Orbits & Approach Earth
- [05:39] Farnocchia uses the swing analogy for orbital resonance:
“If you are in a resonance that your motion has the right timing compared to that of Jupiter or another planet, your orbit kind of gets excited and you might get injected into the inner solar system.”
- Small asteroids routinely enter our atmosphere and burn up; in 2024, four such harmless objects were detected.
6. Actual Impact Rates & Risks
- [06:46] Harford:
“Scientists have used crater formation rates on the Moon to calculate that over the last 600 million years, the Earth has been struck by around 60 objects whose diameter was 5 km or more.”
- 2024 YR4 isn’t a planet killer; it's about 40–90 meters wide—big enough to devastate a city but not cause mass extinction.
- [07:40] Farnocchia provides the updated risk estimate:
"Right now it's 5 in 10 million. Those are the odds. Very, very small.”
7. Why the Numbers Changed—And the Role of Uncertainty
- Early projections had less data, resulting in high uncertainty and seemingly alarming probabilities (up to 3.1%).
- [08:28] Farnocchia explains:
“As we gathered additional observational data, this uncertainty in Position for The asteroid in 2032 became smaller, but the Earth remained inside the swath of possible positions for the asteroid. And so the probability went up because the Earth was occupying a larger fraction of that uncertainty.”
- Over time, as trajectory estimates improved, the likelihood dramatically fell.
8. The "Intersection" Analogy
- [08:59] Harford:
“Think of it as kind of like an intersection, a road junction such as a crossroad. We know where the Earth is... we can’t predict exactly the asteroid. As the weeks have gone by, they've collected more data... and the likelihood of a collision has dropped.”
9. Current (Extremely Low) Odds and Ongoing Monitoring
- [09:32] Farnocchia:
“It's 99.9999999. Whatever.”
- Harford: “It's not going to hit.”
- NASA continues constant surveillance of new asteroids for potential future threats.
10. Should We Be Worried?
- [10:04] Farnocchia reassures listeners:
“Asteroid impacts for asteroids that are capable of causing substantial damage are really unlikely. It's not something that people should lose their sleep over.”
Notable Quotes & Memorable Moments
- [02:30] Tim Harford: “A 1% chance of something really bad is still quite bad, but mostly because shortly after discovery, this 1% likelihood was upgraded to 3%.”
- [04:59] Davide Farnocchia: “Jupiter was pulling enough with its gravity to prevent the formation of another planet between Mars and Jupiter. And so we were left with a bunch of rocks in that ring...”
- [05:39] Davide Farnocchia: “It’s like what kids do when they go on a swing... if your motion has the right timing, your orbit kind of gets excited and you might get injected into the inner solar system.”
- [07:49] Tim Harford: “Very small indeed. So why did everyone get so excited?”
- [09:32] Davide Farnocchia (on current odds): “It's 99.9999999. Whatever.”
- [10:13] Tim Harford: “And with those words of reassurance, we leave you…”
Important Timestamps
- [01:38] — Introduction and media panic over 2024 YR4
- [02:30] — Initial risk estimates and what these numbers mean
- [03:41] — NASA’s Davide Farnocchia on asteroid tracking
- [04:38] — Daily inflow of space material to Earth
- [05:39] — Explanation of orbital resonance and how asteroids enter the inner Solar System
- [07:40] — The actual (very low) probability of impact
- [08:28] — Why initial risk estimates rose before falling
- [08:59] — Intersection analogy clarifies findings
- [09:32] — Current odds: essentially no risk
- [10:04] — Should you be concerned? (No.)
Tone and Language
The episode is factual, calm, and lightly humorous, with Harford’s trademark approachability and Farnocchia’s reassurances against media hype. Technical explanations are made accessible using vivid analogies (swings, crossroads) and down-to-earth language.
Bottom line:
Although asteroid 2024 YR4 briefly made headlines with alarming-sounding risk percentages, more observations have reduced the likelihood of a 2032 impact to vanishingly small levels. NASA’s ongoing tracking systems mean future threats are closely monitored, but there’s no reason to lose sleep over city-sized asteroids—at least not this one.