Asteroids Impacting the Earth | What are the chances?

Image Credit: NASA

As one of the most classic scenarios of space science fictions, an asteroid impacting the Earth’s surface could potentially create dramatic changes to those living on our planet. Depending on the size of the asteroid or extraterrestrial object, the resulting impact could be potentially alter the Earth’s current orbit around the sun or create a significant explosion that could level out major cities in a 200-mile (320 km) radius.

By looking at craters on the Earth’s surface, we have evidence that asteroids have impacted the Earth in the planet’s 4.5 billion year history. What are the chances of asteroids hitting the Earth in the near future?

What are the chances of asteroids hitting Earth?

Image Credit: Simone Marchi

First, it is important understand the importance of Earth’s atmosphere, which is not common to all bodies within our Solar System. Earth’s atmosphere causes a lot of the debris from space to burn up before they hit the Earth’s surface at large sizes.

That’s not to say space debris doesn’t reach the earth’s surface. In fact, that’s far from the truth. Everyday, thousands of tiny debris from space hit the earth — typically the size of a grain of sand or small pebble. So to answer the question about asteroids (defined as any inactive, rocky body orbiting the sun) hitting the earth, the chances are 100% on a daily basis.

On the contrary, if you look at the Moon or Mercury, you can see craters everywhere largely due to their lack of an atmosphere that acts as a buffer between their surfaces and any celestial debris.

Have humans been killed by a meteorite or by the after effects of an impact?

According to NASA, there have been known no humans killed in the past 1,000 years by a meteorite or by a meteorite striking the earth’s surface. There is no record of that happening anywhere on the planet.

However, in Ancient China, there are records of such occurrences. An individual’s chance of getting struck or impacted by a meteorite is very small; however, the risk increases when you deal with regional or global catastrophes that result from objects impacting the surface with a surface area of larger than 1 km2.

Predictions on upcoming asteroids entering the Earth’s atmosphere

According to the European Space Agency’s Risk Page, they share a number of objects that have a non-zero probability of impacting the Earth’s surface, with the soonest object expected to fly near-Earth in 2020.

How many near-Earth asteroids have been discovered in 2019?

According to NASA, the total number of near-Earth asteroids discovered since the beginning of 2019 was around 19,000. On a given week, NASA expects that 30 new asteroids are discovered, making these near-Earth objects a very common occurrence in the grand scheme of things.

The majority of these space rocks have been found as a result of NASA-funded surveys of the skies, mostly by using ground-based telescopes. In 1998, NASA started to actively catalogue these objects.

Potentially hazardous asteroids (PHA)

The qualification of potentially hazardous asteroids, or PHAs, depend on the size of the asteroids. These asteroids measure at least 460 feet or 140 meters across, which large enough to wipe out an entire US state if they were to hit the earth. At the moment, 8,000 PHAs have been discovered and catalogued.

What can we do about asteroids on the path of collision with Earth?

The field of “asteroid impact avoidance” is associated with a number of methods and approaches that can be deployed to divert the path of an asteroid that is on-track to hitting the Earth’s surface. These “near-Earth objects” are referred by acronym as NEOs.

Generally speaking, the two primary strategies focus on either “destruction” or “diversion.”

Destruction of NEOs

Image Credit: NASA

Aptly-named, the destruction of near-Earth objects involve breaking the larger body into harmless fragments that may evaporate as they approach the Earth’s surface. These strategies are typically used against larger objects that may require significant force to re-direct using diversion methods.

  • Nuclear explosive devices: Large nuclear explosion set off on or near the asteroid to break up the object.
  • Concentrated solar energy: Channeling of solar energy to heat an asteroid and vaporize it. Over the span of long durations, this could provide enough energy to deflect the object.
  • Asteroid laser ablation: Similar to concentrated solar energy, a high-powered laser could be used to produce a similar effect.
  • Mass driver: A system that would eject material from the asteroid into space, giving steady pushes away from Earth as well as allowing mass to avoid the earth.

Diversion of NEOs

These techniques are responsible for delaying the asteroids path or advancing the asteroids path. Essentially, these are techniques used to ensure that the path of the asteroid does not intersect the path of the earth.

By slowing down the asteroid, we can create asteroid avoidance by allowing the Earth to pass by as our planet is constantly orbiting the sun. In the same way, we could also speed up the asteroid, but this is generally more difficult to accomplish.

  • Kinetic impact: Hitting an asteroid with another high-mass object to knock it off course.
  • Asteroid tractor: This technique involves adding a small bit of thrust on the asteroid over a long duration to ultimately change its trajectory.
  • Ion beam shepherd: Another technique that involves using a low-divergence ion thruster that is pointed at the object from another lighter spacecraft hovering alongside.
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