An Asteroid Impact Could Wipe Out an Entire City – NASA’s Planetary Defense Plans to Prevent Catastrophe

A giant asteroid hit Earth and wiped out the dinosaurs 65 million years ago.

A space security expert explains NASA’s plans to prevent a potential catastrophe.

The Earth exists in a dangerous environment. Cosmic bodies, such as asteroids and comets, constantly move through space and often crash into our planet. Most of them are too small to pose a threat, but some can be of concern.

As a scholar who studies space and international security, it is my duty to ask how likely an object to crash into the planet really is – and whether governments are spending enough money to prevent a such event.

Finding the answers to these questions requires knowing what near-Earth objects are out there. Nowadays,[{” attribute=””>NASA has tracked only an estimated 40% of the bigger ones. Surprise asteroids have visited Earth in the past and will undoubtedly do so in the future. When they do appear, how prepared will humanity be?

Asteroid Orbits Near Earth

The orbits of thousands of asteroids (in blue) cross paths with the orbits of planets (in white), including Earth’s. Credit: NASA/JPL

The threat from asteroids and comets

Millions of objects of various sizes orbit the Sun. Near-Earth objects include asteroids and comets whose orbits will bring them within 120 million miles (193 million kilometers) of the Sun.

Astronomers consider a near-Earth object a threat if it will come within 4.6 million miles (7.4 million km) of the planet and is at least 460 feet (140 meters) in diameter. If a celestial body of this size crashed into Earth, it could destroy an entire city and cause extreme regional devastation. Larger objects – 0.6 miles (1 km) or more – could have global effects and even cause mass extinctions.

The most famous and destructive impact took place 65 million years ago when a 6-mile (10-km) diameter asteroid crashed into what is now the Yucatán Peninsula. It wiped out most plant and animal species on Earth, including the dinosaurs.

But smaller objects can also cause significant damage. In 1908, an approximately 164-foot (50-meter) celestial body exploded over the Tunguska River in Siberia. It leveled more than 80 million trees over 830 square miles (2,100 square km). In 2013, an asteroid only 65 feet (20 meters) across burst in the atmosphere 20 miles (32 km) above Chelyabinsk, Russia. It released the equivalent of 30 Hiroshima bombs worth of energy, injured over 1,100 people and caused US$33 million in damage.

The next asteroid of substantial size to potentially hit Earth is asteroid 2005 ED224. When the 164-foot (50-meter) asteroid passes by on March 11, 2023, there is roughly a 1 in 500,000 chance of impact.

Near-Earth Asteroid Discovered

NASA has been steadily finding and tracking near-Earth objects since the 1990s. Credit: NASA/JPL-Caltech

Watching the skies

While the chances of a larger cosmic body impacting Earth are small, the devastation would be enormous.

Congress recognized this threat, and in the 1998 Spaceguard Survey, it tasked NASA to find and track 90% of near-Earth objects 0.6 miles (1 km) across or bigger within 10 years. NASA surpassed the 90% goal in 2011.

In 2005, Congress passed another bill requiring NASA to expand its search and track at least 90% of all near-Earth objects 460 feet (140 meters) or larger by the end of 2020. That year has come and gone and, mostly due to a lack of financial resources, only 40% of those objects have been mapped.

As of Feb. 14, 2022, astronomers have located 28,266 near-Earth asteroids, of which 10,033 are 460 feet (140 meters) or larger in diameter and 888 at least 0.6 miles (1 km) across. About 30 new objects are added each week.

A new mission, funded by Congress in 2018, is scheduled to launch in 2026 an infrared, space-based telescope – NEO Surveyor – dedicated to searching for potentially dangerous asteroids.


Smaller asteroids, like the one that exploded over Russia in 2013, can hit Earth without warning, but larger, more dangerous objects have also surprised astronomers.

cosmic surprises

We can only prevent disaster if we know it is coming, and asteroids have snuck past Earth.

A football-field-sized asteroid – dubbed the ‘City-killer’ – passed within 45,000 miles of Earth in 2019. A 747 jet-sized asteroid approached in 2021, as was a 0.6 mile (1 km) wide asteroid in 2012. Each of them was only discovered about a day before passing Earth.

The research suggests that one reason could be that Earth’s rotation creates a blind spot in which some asteroids remain undetected or appear stationary. This can be a problem, as some surprise asteroids we don’t miss. In 2008, astronomers spotted a small asteroid just 19 hours before it crashed into rural Sudan. And the recent discovery of an asteroid 1.2 miles (2 km) in diameter suggests there are still large objects lurking around.

Illustration of double asteroid redirect test

NASA’s DART mission will crash a small spacecraft into the twin asteroid Didymos to see if it will change the asteroid’s orbit. Credit: NASA/Johns Hopkins, APL/Steve Gribben

What can be done?

To protect the planet from cosmic dangers, early detection is essential. At the 2021 Planetary Defense Conference, scientists recommended a minimum of five to ten years of preparation to mount a successful defense against dangerous asteroids.

If astronomers find a dangerous object, there are four ways to mitigate a disaster. The first concerns regional first aid and evacuation measures. A second approach would be to send a spacecraft to fly close to a small or medium-sized asteroid; the craft’s gravity would slowly change the object’s orbit. To alter the trajectory of a larger asteroid, we can either smash something into it at high speed or detonate a nearby nuclear warhead.

These ideas may sound far-fetched, but in November 2021, NASA launched the world’s first large-scale planetary defense mission as a proof of concept: the Double Asteroid Redirection Test, or DART. The large asteroid Didymos and its small moon currently pose no threat to Earth. In September 2022, NASA plans to alter the asteroid’s orbit by crashing a 1,340-pound (610 kg) probe into the moon of Didymos at a speed of about 14,000 mph (22,500 km/ h).

It is also important to know more about the composition of threatening asteroids, as their composition can affect our ability to deflect them. The Bennu asteroid measures 1,620 feet (490 meters) in diameter. Its orbit will bring it dangerously close to Earth on September 24, 2182, and there is a 1 in 2,700 chance of a collision. An asteroid this size could wipe out an entire continent, so to learn more about Bennu, NASA launched the OSIRIS-Rex probe in 2016. The spacecraft arrived in Bennu, took photos, collected samples and is expected to return on Earth in 2023.

Planetary Defense Spending

In 2021, NASA’s planetary defense budget was $158 million. That’s just 0.7% of NASA’s total budget and just 0.02% of the US defense budget of around $700 billion in 2021.

This budget supports a number of missions, including the $83 million NEO Surveyor, $324 million DART, and Osiris Rex at around $1 billion over multiple years.

Is this the right amount to invest in sky monitoring, given that around 60% of all potentially dangerous asteroids go undetected? This is an important question to ask when considering the potential consequences.

Investing in planetary defense is like buying home insurance. The probability of experiencing an event that destroys your home is very low, but people still buy insurance.

If even a single object over 460 feet (140 meters) hit the planet, the devastation and loss of life would be extreme. A larger impact could literally wipe out most species on Earth. Even if no such body is expected to hit Earth in the next 100 years, the odds are not zero. In this low probability versus high consequence scenario, investing in protecting the planet from dangerous cosmic objects can give humanity some peace of mind and could prevent catastrophe.

Written by Svetla Ben-Itzhak, Assistant Professor of Space and International Relations, West Space Seminar, Air War College, Air University.

This article first appeared in The Conversation.The conversation

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