Asteroids Are So Dangerous – And Here’s How To Defend Them

In less than seven years, on April 13, 2029, the asteroid Apophis will hurtle past our planet just 31,750 kilometers away. If the cosmic piece with a diameter of about 350 meters were to hit the Earth, it would release an impact energy of about 900 megatons (TNT equivalent). In comparison, by far the largest nuclear explosion to date, the Soviet Tsar bomb, was equivalent to just 50 megatons of TNT.

On September 30, 2054, an even larger asteroid will approach us: The clump, named after the ancient Egyptian god of the dead, Bennu, is nearly 500 meters in size and has a mass of 62 million tons. An impact from the asteroid discovered in 1999, which is considered one of the most dangerous, would release an energy of 1,400 megatons of TNT – more than 1 million times the strength of the explosion in the port of Beirut in August 2020.

Despite this enormous destructive potential, Apophis and Bennu are not so-called global killers like the huge chunk that struck 66 million years ago in the north of what is now Mexico’s Yucatán Peninsula and thus probably caused the last major mass extinction in Earth’s history, that also killed dinosaurs. The asteroid, estimated to be 14 kilometers in diameter, released an energy equivalent to at least 200 million Hiroshima bombs and left the Chicxulub crater 180 kilometers in diameter that can still be seen today.

Cosmic cars of this caliber could destroy human civilization or even humanity itself. But even smaller chunks like Bennu or Apophis, depending on where they strike, can cause regionally devastating damage and kill millions of people. Although the probability of such an impact is small, the consequences are absolutely fatal if they occur.

Therefore, it seems only reasonable to find methods of defense against the threat from space. The American space agency NASA made an important breakthrough here with its Dart mission: it caused a space probe to deliberately collide with an asteroid for the first time. The Dart probe’s impact on the asteroid moon Dimorphos, some seven million miles away, significantly reduced its orbit around its big brother Didymos.

But what are asteroids, where do they come from? How do the astronomers search for the bombs from space and how high do they estimate the probability of an impact? What are the effects of an impact and what defense methods are there? An overview.

Asteroids are so-called small bodies that are larger than meteoroids but smaller than dwarf planets. Their diameter can therefore vary from a few meters to several hundred kilometers. Their mass is not large enough to reach hydrostatic equilibrium and take on a roughly round shape like dwarf planets; they therefore always have an irregular shape. Asteroids, like planets, move in orbits around the sun.

Most asteroids are located in the so-called main belt between the orbits of the planets Mars and Jupiter. Due to Jupiter’s strong gravitational field, small asteroids continue to penetrate the inner solar system – these so-called near-Earth asteroids (NEAs) move in orbits that can intersect Earth’s orbit. Potentially dangerous are those taller than 140 meters and closer than 7.5 million kilometers to Earth’s orbit – that’s 0.05 AU (astronomical unit; 1 AU corresponds to 149,597,870 km). So they could be on a collision course within 100 years due to orbital perturbations.

The exact number of asteroids cannot, of course, be determined and, moreover, they are not easy to recognize because they are relatively small and often dark. As they move toward Earth from the sun’s direction, they are obscured by the light and become even harder to see. Some asteroids are only discovered a few days before they pass Earth. For example, the asteroid that fell near the Russian city of Chelyabinsk in 2013 was not detected before entering the atmosphere.

In order to recognize the danger from space in time, institutions such as Spacewatch at the University of Arizona and NASA are looking for potentially dangerous celestial bodies. For this, NASA has set up an observation center – the Center for Near-Earth Object Studies (CNEOS) – that records all known asteroids and their orbits. The European Space Agency also operates a near-Earth object coordination center in Italy.

All asteroids larger than 300 meters must be identified and catalogued. So far, about 27,000 of the boulders have been identified near our planet, including about 10,000 with a diameter of more than 140 meters.

Astronomers estimate that they have currently identified about 95 percent of potentially dangerous asteroids near Earth. None of them will be on a collision course with Earth in the coming decades. However, there is always a small danger that even a large car escapes the observers. Of the asteroids, which are more than 140 meters in size, only two-thirds are estimated to have been discovered and tracked.

A look at the moon’s surface shows that asteroid impacts are not uncommon. Earth was also bombarded by asteroids in its early days – it’s possible that even vital water from the edge of the solar system reached Earth using these chunks. There are probably about 22,000 larger craters on Earth, but most are barely recognizable due to the strong erosion – unlike the craters on the moon, where there is no atmosphere. An estimated 25,000 pieces hit the earth every year.

The probability of an impact is of course related to the size of the asteroid; there are more of the smaller ones than of the big ones. According to statistics, an asteroid with a diameter of 30 meters hits about once every 200 years. Larger chunks, more than 1 kilometer in diameter and orbiting dangerously close to Earth, are rarer. Astronomers have counted about 1,100 of these objects, statistically one of which strikes our planet every 500,000 to 10 million years.

A monster like the one that killed the dinosaurs 66 million years ago strikes about every 100 million years. However, astronomers are currently unaware of an asteroid that could go directly to Earth in the near future.

The consequences of an impact naturally depend on the mass of the asteroid and its speed. It also matters where it hits — the asteroid, believed to have exploded in 1908 over the Siberian Tunguska River valley, has done relatively little damage in this very sparsely populated area.

An asteroid 350 meters in diameter would leave a crater 6 kilometers in diameter and devastate an area the size of the canton of Valais. The impact energy would be between 1 and 10 gigatons of TNT. A lump five times larger with a diameter of 1.75 kilometers would already cause a global catastrophe: an area the size of France would be immediately destroyed; Dust and soot thrown into the atmosphere would lead to strong global cooling – an “impact winter” – and destroy the ozone layer.

An impact in the ocean would result in a mega-tsunami with a wave height of more than 100 meters at the point of origin. This tidal wave would inundate entire coastal landscapes and their hinterland over a large area. The whole of humanity would be affected by the consequences of the impact of such a car. In the event of an impact of a gigantic caliber more than ten kilometers in size, human civilization would have been destroyed; larger chunks could even wipe out life on Earth altogether.