An asteroid impact could wipe out entire cities — what can we do to prevent that?
A space security expert explains NASA’s plans to protect our planet
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 themwithin 120 million miles(193 million kilometers) of the Sun.
Astronomers consider a near-Earth object a threat if it willcome 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) diameterasteroid crashed into what is now the Yucatán Peninsula. Itwiped out most plant and animal specieson Earth, including the dinosaurs.
But smaller objects can also cause significant damage. In 1908, an approximately 164-foot (50-meter) celestial body exploded over theTunguskariver in Siberia. Itleveledmore 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 peopleand 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 a1 in 500,000 chance of impact.
Watching the skies
While thechances of a larger cosmic body impacting Earth are small, the devastationwould be enormous.
Congress recognized this threat, and inthe 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. NASAsurpassed the 90% goalin 2011.
In 2005,Congress passed another billrequiring 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 toa lack of financial resources, only40% of those objects have been mapped.
As of Feb. 14, 2022,astronomers have located 28,266near-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. About30 new objectsare 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 tosearching for potentially dangerous asteroids.
Cosmic surprises
We can only prevent a disaster if we know it is coming, and asteroids have sneaked up on Earth before.
An asteroid the size of a football field – dubbed the “City-killer” – passedless than 45,000 milesfrom Earth in 2019. An asteroid the size of a 747 jetcame closein 2021 as did a 0.6-mile (1-km) wideasteroidin 2012. Each of these was discovered onlyabout a daybefore they passed Earth.
Research suggests that one reason may be that Earth’s rotationcreates a blind spotwhereby some asteroids remain undetected or appear stationary. This may be a problem, as some surprise asteroids do not miss us. In 2008, astronomers spotted a smallasteroidonly 19 hours before it crashed into rural Sudan. And the recentdiscoveryof an asteroid 1.2 miles (2 km) in diameter suggests that there are still big objects lurking.
What can be done?
To protect the planet from cosmic dangers, early detection is key. At the 2021 Planetary Defense Conference, scientists recommended a minimum offive to 10 years’ preparation timeto mount a successful defense against hazardous asteroids.
If astronomers find a dangerous object, there arefour waysto mitigate a disaster. The first involves regional first-aid and evacuation measures. A second approach would involve sending a spacecraft to fly near a small- or medium-sized asteroid; the gravity of the craft would slowly change the object’s orbit. Tochange a bigger asteroid’s path, we can either crash something into it at high speeds or detonate a nuclear warhead nearby.
These may seem like far-fetched ideas, but in November 2021, NASA launched the world’s first full-scale planetary defense mission as a proof of concept: theDouble Asteroid Redirection Test, or DART. Thelarge asteroid Didymosand its small moon currently pose no threat to Earth. In September 2022, NASA plans to change the asteroid’s orbit by crashing a 1,340-pound (610 kg) probe into Didymos’ moon at a speed of approximately 14,000 mph (22,500 kph).
Learning more about what threatening asteroids are made of is also important, as their composition may affect how successful we are at deflecting them. Theasteroid Bennuis 1,620 feet (490 meters) in diameter. Its orbit will bring it dangerously close to Earth on Sept. 24, 2182, and there is a1 in 2,700chance of a collision. An asteroid of this size could wipe out an entire continent, so to learn more about Bennu, NASA launched theOSIRIS-Rexprobe in 2016. The spacecraft arrived at Bennu, took pictures, collected samples and is due to return to Earth in 2023.
Spending on planetary defense
In 2021, NASA’s planetary defense budget was$158 million. This is just0.7%of NASA’stotal budgetand just 0.02% of the roughly$700 billion 2021 U.S. defense budget.
This budget supports a number of missions, including the NEO Surveyor at$83 million, DART at$324 millionand Osiris Rex at around$1 billionover several years.
Is this the right amount to invest in monitoring the skies, given the fact that some60% of all potentially dangerous asteroids remain undetected? This is an important question to ask when one considers the potential consequences.
Investing in planetary defense is akin to buying homeowners insurance. The likelihood of experiencing an event that destroys your house is very small, yet people buy insurance nonetheless.
If even a single object larger than 460 feet (140 meters) hits the planet, the devastation and loss of life would be extreme. A bigger impact could quite literally wipe out most species on Earth. Even if no such body is expected to hit Earth in thenext 100 years, the chance is not zero. In this low likelihood versus high consequences scenario, investing in protecting the planet from dangerous cosmic objects may give humanity some peace of mind and could prevent a catastrophe.
This article bySvetla Ben-Itzhak, Assistant Professor of Space and International Relations, West Space Seminar, Air War College,Air Universityis republished fromThe Conversationunder a Creative Commons license. Read theoriginal article.
Story byThe Conversation
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