From: veritasium
The Earth is constantly bombarded by debris from space. These impacts, ranging from small to catastrophic, have significant effects on Earth and astronomical bodies.
Recent Impact: The Chelyabinsk Event
On February 15, 2013, an asteroid heavier than the Eiffel Tower struck Earth’s atmosphere over Chelyabinsk, Russia [00:00:15]. This Chelyabinsk asteroid event exploded 30 kilometers above the ground, producing a flash brighter than the sun [00:00:24]. The explosion was silent for 90 seconds due to its height, which worsened the devastation [00:00:32]. People looking out windows were injured when a shockwave hit, blowing out glass [00:00:52]. The shockwave damaged thousands of buildings and injured 1500 people [00:01:03].
Embarrassingly, this event occurred on the same day scientists had predicted a different asteroid, Duende, would make a close fly-by of Earth [00:01:08]. Duende came within 27,000 kilometers of Earth’s surface, closer than geosynchronous satellites [00:01:24]. Despite correctly predicting Duende’s approach, they completely missed the unrelated asteroid that exploded over Russia [00:01:36].
Since 1988, over 1200 asteroids larger than a meter have collided with Earth, but only five were detected before impact, never with more than a day’s warning [00:01:49].
Origin and Detection of Asteroids
Asteroids are the leftover debris from the formation of our solar system 4.5 billion years ago [00:02:35]. They formed from rocks and dust clumping into molten protoplanets, which then collided and broke into smaller fragments [00:03:05]. This origin explains why some asteroids are rocky rubble piles, while others, from the cores of planetesimals, are mostly metal [00:03:27]. An iron meteorite is essentially a piece of a small planetary body’s core [00:03:41].
Most asteroids have stable orbits in the main asteroid belt between Mars and Jupiter [00:04:06]. However, some have moved closer to Earth, becoming Near Earth Objects (NEOs) [00:04:18]. Stephen Hawking considered an asteroid impact to be the greatest threat to life on Earth [00:04:28].
Challenges in Detection
Finding asteroids is difficult for several reasons:
- Visibility: Most are spotted by ground-based telescopes looking for “moving dots” against static stars and galaxies [00:04:39].
- Size: Asteroids range from meters to kilometers in size and are hard to spot in the vastness of space [00:04:58]. The Chelyabinsk meteor was only about 20 meters in diameter [00:05:12].
- Reflectivity: They are rough and dark, reflecting only about 15% of the light that hits them [00:05:19]. They are best seen when fully illuminated by the sun, which means 85% of detected NEOs are found in the 45 degrees of sky directly opposite the sun (the opposition effect) [00:05:32]. This means any asteroid approaching from the direction of the sun, like Chelyabinsk, is nearly impossible to see [00:05:51].
While a million asteroids have been cataloged, only 24,000 are NEOs [00:06:03].
Orbital Prediction Difficulties
Even after detection, predicting an asteroid’s trajectory is challenging [00:06:22]:
- Limited Data: Early observations provide only a small arc of motion, making long-term prediction difficult [00:06:27]. Years of observations are needed [00:06:36].
- Dynamical Chaos: Planetary gravity constantly influences asteroid orbits, leading to “dynamical chaos” [00:06:54]. This means predictions are generally accurate for a maximum of about 100 years into the future [00:07:10].
Consequences of Impact
The history of significant asteroid impacts shows dramatic results.
Barringer Crater
Barringer Crater in Arizona, named after Daniel Barringer, was formed by an iron meteorite impact [00:07:33]. Barringer mistakenly believed the meteorite would be intact and attempted to mine it [00:07:56]. However, when an impact occurs at high speed (e.g., 30 kilometers per second), the kinetic energy is so immense that it completely vaporizes the projectile [00:08:39]. The superheated, high-pressure gas then explodes, creating the crater [00:09:03]. The 50-meter asteroid that formed Barringer Crater (only slightly larger than Chelyabinsk) released energy equivalent to 10 megatons of TNT, over 600 times the energy of the Hiroshima bomb [00:09:35]. Thus, an asteroid impact closely resembles a large nuclear explosion [00:09:49].
Dinosaur Extinction Event
The dinosaurs were wiped out by a 10-kilometer asteroid impact approximately 65 million years ago [00:10:16]. Asteroids above a critical size (a couple of kilometers) deliver enough energy to have a global effect [00:10:23]. Such an impact launches debris into sub-orbital trajectories that fall back to Earth globally [00:10:39]. This phenomenon causes the entire sky to light up with “wall-to-wall meteors,” turning the sky into a “red, hot glow” like being inside a toaster oven [00:10:53]. The intense heat would “cook everything on the ground,” allowing only animals living underground or in water to survive [00:11:18].
Future Impact Probabilities
- 10-kilometer asteroid (like the KT extinction event): The chance of dying from such an impact in your lifetime is effectively zero, as no 10-kilometer impactors are predicted to intersect Earth’s path for the next 100 years [00:11:51].
- 1-2 kilometer asteroids: These are capable of causing massive local damage, equivalent to obliterating a country the size of France or Germany [00:12:49]. We believe we have identified 90-98% of these bodies and can make reasonable predictions for their orbits for the next 10 years [00:13:17].
- Hundred-meter asteroids: This size poses a significant threat. They are large enough to obliterate a major city, causing buildings to collapse, city-wide fires, and high-speed ejecta that would devastate a hundred-kilometer zone around the impact site [00:13:49]. We are missing a lot of these projectiles, and an impact from one “could happen tomorrow” [00:13:57].
Deflection Strategies
Currently, there are no effective current and potential asteroid deflection strategies for kilometer-sized or larger asteroids [00:16:26]. Options considered include:
- Bombing: Blowing up an asteroid is problematic as fragments would likely re-form into a rubble pile due to gravity [00:14:48].
- Rocket Nudging: Attaching a rocket to gently push an asteroid aside is impractical due to the massive thrust required and the need for rockets to remain attached for centuries [00:15:22].
- Ablation with Lasers: Boiling off the surface with lasers is not feasible with current technology; we lack sufficiently powerful lasers that could be transported to the asteroid [00:15:53].
- Wrapping in Foil: Covering an asteroid in reflective foil to change its radiative properties and nudge its orbit is also not currently achievable due to the scale of material and deployment challenges [00:16:06].
Even the most hopeful strategy, evacuating a city, is extremely difficult for a large metropolitan area due to traffic congestion and the inability to move millions of people quickly [00:17:10].
The most practical immediate step is to enhance detection capabilities: “Let’s do the surveys. Let’s build the telescopes. Let’s put this telescope in space. That will be a major contribution to understanding the threat from the asteroids” [00:17:50]. Once a dangerous object is identified, focused efforts can then begin to develop deflection methods [00:18:04].