Asteroidų ir kometų smūgiai

Strokes of asteroids and comet

Historical collisions (e.g., the event that led to the extinction of the dinosaurs) and the current Earth threat assessment system

Space guests and the danger posed by impacts

There is evidence in the Earth's geological history and craters that asteroids and comets Impacts occur throughout geological time. Although large impacts are rare in human history, they sometimes significantly alter the planet's environment, causing mass extinctions or climate change. In recent decades, scientists have realized that even smaller impacts that are dangerous to a city or region pose a significant risk, and systematic studies have been launched searches and observations, to detect near-Earth objects (NEOs). By studying past events — for example, The Chicxulub impact (~66 million years ago), which probably led to the extinction of the Neavian dinosaurs — and by observing the current sky, we are trying to prevent future catastrophes and make sense of the Earth's deeper cosmic context.

2. Impactors: Asteroids and Comets

2.1 Asteroids

Asteroids are mainly rocky or metallic bodies, usually concentrated in the main asteroid belt between Mars and Jupiter. Some, called near-Earth asteroids (NEAs), orbits are such that they approach the Earth. Their size can range from a few meters to hundreds of kilometers. They can be carbonaceous (C-type), silicate (S-type), or metallic (M-type) in composition. Due to gravitational perturbations or collisions with planets (especially Jupiter), some asteroids escape from the main ring and cross the vicinity of Earth's orbit.

2.2 Comets

Comets usually has more volatile ices (water, CO2, CO, etc.) and dust. They form in distant regions of the Solar System, for example, In the Kuiper Belt or remote In the Oort cloudWhen gravitational perturbations push them toward the inner solar system, the melting of the ice creates comas and tails. Short-period comets (up to a period of ~200 years) often originate from the Kuiper belt, and long-term come from the Oort cloud, which can only return every few or even tens of thousands of years. Although they are rarer near Earth, their collision speeds are usually higher — so the potential damage would be greater (although the comet's density is often lower).

2.3 Different characteristics of strokes

  • Asteroid impacts: Typically slower (up to ~20 km/s near Earth), but can be massive or iron-rich, creating large craters and strong shock waves.
  • Comet impacts: Can reach speeds of up to ~70 km/s, so even if the density is lower, the total kinetic energy (and thus the impact) is often higher.

Both categories can pose a risk — asteroids are more commonly mentioned in history for major collisions, but comets can also strike at dangerously high speeds.

3. Major collisions of historical times: the K–Pg event and others

3.1 K–Pg boundary event (~66 million years ago)

One of the most famous blows — Chicxulub event Cretaceous–Paleogene (K–Pg) border, most likely causing the extinction of the Neavian dinosaurs and ~75 % loss of other species. About 10–15 km in diameter (mostly of asteroid origin) struck near the Yucatan Peninsula, knocking out ~180 km diameter crater. The impact caused:

  • Shock waves, global fallout from the ejected material, and giant fires.
  • Dust and aerosols rising to the stratosphere, obscuring sunlight for months or years, paralyzing ecosystems that rely on photosynthesis.
  • Acid rain after the evaporation of sulfurous rocks.

This has caused a global climate crisis, as evidenced by iridium anomaly in sediments and impact quartz. This remains the most striking example of how an impact can change the entire biosphere of Earth [1], [2].

3.2 Other examples and structures of impacts

  • Vredfort Dome (South Africa, ~2 billion years old) and Sudbury Basin (Canada, ~1.85 billion years old) – the oldest powerful craters, formed billions of years ago.
  • Chesapeake Bay Crater (~35 million years) and Popigai Crater (Siberia, ~35.7 million years ago) were likely associated with multiple Late Eocene bombardment.
  • Tunguska event (Siberia, 1908): A small (~50–60 m) rocky or cometary fragment exploded in the atmosphere, knocking down about 2000 km2 forests. No crater was formed, but it showed that even relatively small bodies can cause powerful explosions in the air.

Smaller impacts occur more frequently (e.g., the 2013 Chelyabinsk meteorite), usually causing only local damage but not global impacts. However, geological records suggest that large events are an integral part of Earth's past (and likely future).

4. Physical effects of shocks

4.1 Crater formation and ejected material

During a high-speed impact, kinetic energy is converted into a shock wave, forming temporary crater. Later, the crater slopes may collapse, creating complex structures (rings, central "domes" in larger craters). Ejected rock fragments, molten particles, and dust can spread worldwide if the impact is powerful enough. In some places, melt deposits form on the crater floor, and tektites may fall on other continents.

4.2 Atmospheric and climatic disturbances

Large impacts eject dust and aerosols (as well as sulfur compounds if the rock is rich in sulfates) into the stratosphere. As a result The Sun is eclipsed., a temporary global cooling (the so-called "shock winter") begins, lasting months or years. In some cases, the released CO2 from carbonate rocks can warm the atmosphere for longer, but the first stage is usually dominated by aerosol-induced cooling. Ocean acidification and a major decline in primary production may occur, as suggested by the K–Pg extinction scenario.

4.3 Tsunamis and giant fires

If the impact falls into the ocean, it creates giant tsunamis, which can reach distant shores. The storms caused by the shock wave and the fragments thrown into the atmosphere can cause global fires (like the Chicxulub impact) that scorch continental vegetation. The combination of these phenomena – tsunamis, fires, climate change – can rapidly devastate ecosystems around the world.

5. Current Earth Threat Assessment System

5.1 Near-Earth Objects (NEO) and Potentially Hazardous Objects (PHO)

Asteroids/comets with perihelion <1.3 AV, called near-Earth objects (NEO)Among them potentially dangerous objects (PHO) are those with a minimum orbital distance to Earth (MOID) <0.05 AV, and diameters typically >~140 m. Impacts of such bodies on Earth could have regional or even global consequences. The largest known PHOs are several kilometers in diameter.

5.2 Search and monitoring applications

  • NASA CNEOS (Center for Near Earth Object Studies) uses projects such as Pan-STARRS, ATLAS whether Catalina Sky Survey to detect new NEOs. ESA and other institutions are conducting similar observations.
  • Orbit determination and probability of impact The calculation is based on repeated observations. Even small inaccuracies in the orbital elements can significantly change the object's possible future position.
  • NEO approval: When a new object is discovered, subsequent observations reduce uncertainties. If a potential collision risk is detected, orbital calculations are revised.

Institutions like NASA Planetary Defense Coordination Office (Planetary Defense Coordination Office) coordinates efforts to identify objects that could pose a threat within a century or more.

5.3 Scale of potential consequences by magnitude

  • 1-20 m: Mostly burns up in the atmosphere or causes local air explosions (e.g. ~20 m Chelyabinsk case).
  • 50–100 m: Potential for city-scale destruction (Tunguska-type explosion).
  • >300 m: Regional or continental catastrophe, in the case of an oceanic impact – large tsunamis.
  • >1km: Global climate impact, potential mass extinctions. Extremely rare (~every 500 thousand - 1 million years 1 km in size).
  • >10 km: Extinction-level events (similar to Chicxulub). Very rare, every tens of millions of years.

6. Security strategies and planetary defense

6.1 Diversion vs. detonation

Given enough time (years or decades), missions that would alter the trajectory of a potentially hazardous NEO could be considered:

  • Kinetic impactor: A probe "bullet" hitting an asteroid at high speed changes the velocity of the body.
  • Gravity "tractor": The probe "hovered" near the asteroid, gradually pulling it in through mutual gravity.
  • Ion beam "shepherd" whether laser vaporization: The engines/lasers used create a small but constant thrust.
  • Nuclear option: An extreme measure (results difficult to predict), an explosive could destroy or dislodge a large object, but there is a risk of particle dispersion.

6.2 The importance of early detection

All referral ideas needed early detection. If the impact is close, the measures are no longer effective. Therefore, it is extremely important to constantly monitor the sky and improve orbital calculations. There are global response plans that call for evacuation (if the object is small) or testing deflector technologies (if there is time).

6.3 Real-life mission experiences

NASA DART mission (Double Asteroid Redirection Test) demonstrated the kinetic impactor method on the small moon Dimorph, orbiting the asteroid Didyma. The mission successfully repositioned its orbit, providing real-world momentum transfer data and confirming that the method can be effective for deflecting medium-sized NEOs. Other concepts are under investigation.

7. Historical context: cultural and scientific perception

7.1 Early skepticism

It is only in the last two centuries that scientists have widely accepted that craters (such as Barringer Crater in Arizona) can be created by impacts. Initially, many geologists thought that they were volcanic in origin, but Eugene Shoemaker and others have shown evidence of shock metamorphism. In the late 20th century, a link was established between asteroids/comets and mass extinctions (e.g., K–Pg), changing the view that large catastrophic impacts did indeed influence Earth's history.

7.2 Public attention

Big impacts, previously considered only distant theoretical possibilities, became known to everyone after SL9 (Shoemaker–Levy 9) comet collision with Jupiter in 1994 and in famous movies (Armageddon, Deep Impact). Today, government agencies often announce news of near misses, thus emphasizing the importance of "planetary defense".

8. Conclusion

Asteroid and comet impacts have caused many twists in Earth's geology, the most prominent example being the Chicxulub event, which drastically changed the course of evolution and ended the Mesozoic Era. Although they are rare from the perspective of humanity, they remain a real threat — near-Earth objects, even relatively small ones, can cause enormous damage on a local scale, and even larger space "intruders" can cause a global catastrophe. Continuous object detection and monitoring activities, enhanced by modern telescopes and data analysis, allow for earlier identification of potential collision paths, which paves the way for mitigation measures (e.g. kinetic impactors).

The ability to detect and potentially deflect a dangerous celestial body marks a new stage: humanity can protect not only itself, but also the entire biosphere from cosmic collisions. Understanding such collisions is important not only for safety reasons, but also allows us to better understand the essential elements of Earth's evolution and the dynamic nature of the cosmic environment - a reminder that we live in a changing solar system, where gravitational "dances" and rare but sometimes epic visitors from space shape our world.

References and further reading

  1. Alvarez, L. W., et al. (1980). "Extraterrestrial cause for the Cretaceous–Tertiary extinction." Science, 208, 1095–1108.
  2. Schulte, P., et al. (2010). "The Chicxulub asteroid impact and mass extinction at the Cretaceous–Paleogene boundary." Science, 327, 1214–1218.
  3. Shoemaker, E. M. (1983). "Asteroid and comet bombardment of the earth." Annual Review of Earth and Planetary Sciences, 11, 461–494.
  4. Binzel, R. P., et al. (2015). "Compositional constraints on the collisional evolution of near-Earth objects." Icarus, 247, 191–217.
  5. Chodas, PW, & Chesley, SR (2005). "Precise prediction and observation of Earth encounters by small asteroids." Proceedings of the International Astronomical Union, 1, 56–65.
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