Would a Large Asteroid or Comet Impact Send a Significant Portion of Energy to Space?

The Earth's surface is occasionally bombarded by asteroids and comets, albeit rarely. However, would a substantial impact release a significant portion of the asteroid's energy into space immediately?

Impact Dynamics vs. Theia Collision

While most asteroid or comet impacts on Earth release only a minimal amount of energy into space, the situation changes dramatically considering events on a planetary scale. A notable example is the Theia collision, which occurred approximately 4.7 billion years ago. This event was so massive that it played a crucial role in the formation of the Moon. Such collisions are extremely rare in our current era, making them extraordinary examples of catastrophic geological consequences.

Energy Distribution in Impact Events

During an asteroid impact, the energy is primarily transferred to the planet rather than being radiated into space. Here's a detailed look at what happens:

Only a small fraction of the energy is immediately radiated away. This includes electromagnetic radiation (light, heat), and possibly some radio emission. In very energetic collisions, some hot material can be ejected into space, but usually, this is not a significant percentage of the total mass of the asteroid. The impact can result in a flash of light and a warm glow from the ejected hot material. Almost all of the asteroid's kinetic energy is absorbed by the Earth and its atmosphere. Over time, this absorbed energy is radiated away as infrared radiation, gradually bringing the Earth back into thermal equilibrium.

Immediate Radiative Loss vs. Thermodynamic Equilibrium

For a significant portion of the asteroid's energy to be radiated into space immediately, two unusual scenarios could occur:

The asteroid would need to be ejected from the Earth's gravitational field (a glancing blow), retaining most of its kinetic energy. This is unlikely but not impossible. Alternatively, the asteroid could strike with such force that it completely splatters the planet, sending the fragments flying away into space. This is much less likely but possible for very massive impacts.

These extreme scenarios would require the asteroid to be traveling at a velocity close to the speed of light, which is far beyond the typical velocity of objects in our solar system.

Earth's Energy Radiative Balance

It's worth noting that the Earth continuously radiates heat into space. This is an ongoing process that occurs at a rate comparable to the energy received from the Sun. Due to global warming, the current equilibrium is slightly tilted such that the Earth is receiving more energy than it is radiating. Increasing temperatures lead to a higher rate of heat radiation.

Following an asteroid impact, the Earth would initially radiate more heat quickly. This is because the heat is concentrated in localized areas post-impact. As time passes, the heat spreads throughout the atmosphere and surrounding crust. This process leads to a drop in temperature, resulting in a lower rate of radiation. In other words, while a significant amount of heat would be released, it would not all be radiated into space immediately.

If the atmosphere were to be completely removed, the Earth would radiate heat much more effectively, as the atmosphere is a good insulator, trapping heat and contributing to the slower loss of energy.