How NASA Works to Detect and Deflect Killer Asteroids

Asteroid near earth - 3D render
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Asteroids and comets speeding around the Sun in orbits that periodically allow them to approach the Earth are called Near-Earth Objects (NEOs). According to the National Aeronautics and Space Administration (NASA), asteroids larger than about 100 meters hit the Earth’s surface on an average of every 10,000 years causing localize disasters. Every several hundred thousand years, asteroids larger than a kilometer (0.62 miles) hit the Earth causing global disasters. And, of course, it is known that at least once, an asteroid strike—the K/T Extinction Event—has left the Earth nearly lifeless. With this threat of devastation in mind, NASA’s Near-Earth Objects program seeks to find and study these asteroids and most importantly, figure out exactly where they are going.

Detecting and Tracking Dangerous Asteroids

While given less than a one in 250,000 chance of actually hitting the Earth, scientists at NASA's Near Earth Object (NEO) program have no intention of turning their backs on any of the Potentially Hazardous Asteroids discovered so far.

Using the Sentry System developed by NASA's Jet Propulsion Laboratory, NEO observers continually scan the most current asteroid catalog to identify those objects with the greatest potential to hit the Earth over the next 100 years. These most threatening asteroids are cataloged in the Current Impact Risks database.

To each near-Earth approaching object, NEO assigns a risk of impact factor based on the Torino Impact Hazard Scale. According to the ten-point Torino scale, a rating of zero indicates the event has "no likely consequences." A Torino Scale rating of 1 indicates an event that "merits careful monitoring." Even higher ratings indicate that progressively more concern is warranted.

To further study near-Earth orbiting objects, their potential threats, and ways in which they may be prevented from impacting the Earth, NASA is currently undertaking this fascinating group of Spacecraft Missions to Asteroids.

For professional and amateur asteroid trackers, JPL's Solar System Dynamics Group provides this handy set of software tools.

Protecting Earth from Asteroid Strikes

Calling them "the only major natural hazard that we can effectively protect ourselves against," NASA has suggested two possible methods of protecting the Earth from an asteroid or comet determined to be on a collision course.

  • Destroying the object before it hits the Earth
  • Deflecting the object from its orbit before it hits the Earth

To destroy the Earth-approaching object, astronauts would land a spacecraft on the surface of the object and use drills to bury nuclear bombs deep below its surface. Once the astronauts were a safe distance away, the bomb would be detonated, blowing the object to pieces. Drawbacks to this approach include the difficulty and danger of the mission itself and the fact that many of the resulting asteroid fragments might still hit the Earth, resulting in massive damage and loss of life.

In the deflection approach, powerful nuclear bombs would be exploded up to half a mile away from the object. The radiation created by the blast would cause a thin layer of the object on the side nearest the explosion to vaporize and fly into space. The force of this material blasting into space would "nudge" or recoil the object in the opposite direction just enough to alter its orbit, causing it to miss the Earth. The nuclear weapons needed for the deflection method could be launched into position well in advance of the object's projected Earth impact.

Best Defense is Adequate Warning

While these and other methods of protection have been considered, no definite plans have been fully developed. Scientists of the Asteroid and Comet Impact division of NASA's Ames Research Center warn that at least ten years will be needed to send a spacecraft to intercept an incoming object and deflect or destroy it. To that end, scientists say, NEO's mission of detecting threatening objects is critical to survival.

"In the absence of active defense, warning of the time and place of an impact would at least allow us to store food and supplies and to evacuate regions near ground zero where damage would be the greatest," says NASA.

What is the Government Doing About This?

In 1993 and again in 1998, Congressional hearings were held to study the impact hazard. As a result, both NASA and the Air Force are now supporting programs to discover Earth-threatening objects. Congress currently budgets only about $3 million per year for programs like the Near Earth Object (NEO) project. While other governments have expressed concern about the impact hazard, none have yet funded any extensive surveys or related defense research.

That Was Close!

According to NASA, a soccer field-sized asteroid came within a mere 75,000 miles of Earth in June 2002. Missing us by less than one-third of the distance to the moon, the asteroid's approach was the closest ever recorded by an object of its size. 

How Many NEOs are There Now?

As of January 3, 2020, the number of near-Earth asteroids discovered by NASA totaled 21, 725. Of these, 8,936 were at least 140 meters in size, while 902 were at least 1 kilometer (0.62 miles) in size and capable of causing massive destruction and loss of life. On average, at least 30 new near-Earth asteroids are discovered every week. NASA’s Center for NEO Studies provides up-to-date asteroid discovery statistics.