Overview of Asteroooooid De-FENSE!
This episode of Stuff You Should Know explains what asteroids are, why scientists track them so closely, and how humanity might defend Earth if a dangerous one were ever found on a collision course. The hosts cover asteroid types, current monitoring systems, major historic impacts like the Chicxulub event, and the most realistic deflection strategies NASA and other agencies are testing.
What Asteroids Are and Why They Matter
Asteroids are small rocky bodies in the solar system, likely either:
- leftover building blocks from planet formation that never became planets, or
- fragments of larger bodies shattered early in solar system history
Most are in the asteroid belt between Mars and Jupiter, but some are nudged into Earth-crossing orbits.
Key asteroid categories discussed
- Near-Earth objects (NEOs): Asteroids whose orbits bring them close to Earth
- Potentially hazardous asteroids (PHAs): Larger objects that come close enough to warrant close monitoring
- Extinction-class asteroids: Objects large enough to potentially wipe out most or all life on Earth
Why NASA Tracks Them So Closely
The hosts stress that Earth has been hit before and will be hit again eventually, so the goal is early detection and, if needed, deflection.
Important numbers and thresholds
- Over 1.8 million known asteroids
- About 25,000 near-Earth asteroids
- Roughly 1,100 new near-Earth asteroids discovered each year
- PHAs are typically defined as objects over 140 meters / 460 feet wide that come within 4.6 million miles of Earth
- Extinction-class asteroids are about 10 km / 6.2 miles wide or larger
Notable close approaches
- The episode mentions Apophis, which will make an extremely close pass in 2029
- NASA maintains a close approaches list to track future risk
The Threat Level: How Bad Could It Get?
The discussion breaks asteroid impacts down by size:
- House-sized asteroid: Could cause city-level destruction
- Mile-wide asteroid: Could produce a global catastrophe and massive climate effects
- 6–8 mile-wide asteroid: Potentially extinction-level, similar to the dinosaur-killing impact
- Much larger impacts: Could theoretically sterilize the planet
They note that even smaller objects can be devastating depending on speed, angle, and where they hit.
The Chicxulub Impact: Earth’s Most Famous Asteroid Disaster
A major portion of the episode focuses on the asteroid impact that likely ended the age of the dinosaurs 66 million years ago.
What happened
- The impact site is now known as the Chicxulub crater
- It is located near the Yucatán Peninsula
- The crater is roughly 112–124 miles across
- The impactor was likely around 8.7 miles / 14 km wide
- It released energy equivalent to about 100 million megatons
Consequences described
- A massive tsunami formed within seconds
- Rock and debris were vaporized and thrown into the atmosphere
- A long-lasting impact winter blocked sunlight
- Oceans became dramatically more acidic
- Roughly 75% of species died out
The hosts note that this catastrophe cleared ecological space for mammals to diversify, eventually leading to humans.
How Scientists Might Defend Earth
The episode lays out the main asteroid-defense ideas NASA and others have studied.
1. Nuclear options
A nuclear bomb on or inside an asteroid is generally not ideal, because it may just break the object into still-dangerous pieces.
A better idea is a standoff nuclear explosion near the asteroid’s surface, which could vaporize material and nudge it off course.
2. Kinetic impactor
This is the most practical idea currently tested:
- A spacecraft is launched to slam into the asteroid
- The collision slightly changes the asteroid’s trajectory
- Even tiny changes add up over years or decades
3. Laser or sunlight heating
Another idea is to heat part of the asteroid so material vaporizes and creates a tiny thrust effect. The hosts describe this as a kind of space-based “death ray” or solar laser.
4. Gravitational tractor
A spacecraft could hover near an asteroid for a long time and use its own gravity to slowly tug the asteroid onto a new path.
Real Missions That Proved the Concept
Project NEAR
NASA’s Near Earth Asteroid Rendezvous (NEAR) mission:
- launched in 1996
- studied Mathilde
- later orbited 433 Eros
- eventually landed on Eros and sent back valuable data
This mission showed that spacecraft can rendezvous with and study asteroids closely enough to support future deflection missions.
DART
The Double Asteroid Redirection Test (DART) was the key proof-of-concept mission.
- launched in 2021
- intentionally crashed into Dimorphos
- demonstrated that a spacecraft impact can alter an asteroid’s orbit
The change was tiny in the moment, but measurable and meaningful over time—exactly the kind of nudge that could matter if Earth had years or decades of warning.
Main Takeaways
- Asteroids are common, and some do cross Earth’s path.
- Most are not dangerous, but a small fraction could be catastrophic.
- NASA and other agencies are actively monitoring near-Earth objects.
- We already have viable strategies to deflect a threat if we get enough warning.
- The most important ingredient is early detection.
Final Thought
The episode’s core message is reassuring: asteroid impacts are a real threat, but humanity is no longer helpless. With modern telescopes, tracking systems, and tested deflection methods like DART, we are far better prepared than any civilization before us.