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NASA crashes a spacecraft into an asteroid to test a plan that could one day save Earth from disaster

On September 26, 2022, NASA plans to alter the orbit of an asteroid.

The large binary asteroid Didymos and its moon Dimorphos currently pose no threat to Earth. But by crashing a 1,340-pound (610-kilogram) probe into the moon of Didymos at a speed of around 14,000 mph (22,500 km/h), NASA will complete the world’s first large-scale planetary defense mission. scale to the world as a proof of concept. This mission is called the Double Asteroid Redirection Test, or DART.

I’m an academic who studies space and international security, and it’s my job to ask what is the real probability of an object crashing into the planet – 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. To date, NASA has only tracked about 40% of the larger ones. Surprise asteroids have visited Earth in the past and no doubt will in the future. Experiments like the DART mission can help prepare humanity for such an event.

The orbits of thousands of asteroids (in blue) cross the orbits of planets (in white), including that of the Earth.

The threat of asteroids and comets

Millions of cosmic bodies, such as asteroids and comets, orbit the Sun and often crash into Earth. Most of them are too small to pose a threat, but some can be of concern. 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 comes within 4.6 million miles (7.4 million kilometers) of the planet and is at least 460 feet (140 meters) tall ) of diameter. If a celestial body of this size were to crash into Earth, it could destroy an entire city and cause extreme regional devastation. Larger objects – 0.6 miles (1 kilometer) or more – could have global effects and even cause mass extinctions.

The most famous and destructive celestial impact took place 65 million years ago when a 10 kilometer 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, a celestial body about 164 feet (50 meters) exploded over the Podkamennaya Tunguska River in Siberia. He leveled more than 80 million trees over 830 square miles (2,100 square kilometers). In 2013, an asteroid just 65 feet (20 meters) in diameter erupted into the atmosphere 20 miles (32 kilometers) above Chelyabinsk, Russia. It released the energy equivalent of 30 Hiroshima bombs, injured more than 1,100 people and caused $33 million in damage.

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

Watch the sky

Although the chances of a larger cosmic body hitting Earth are low, the devastation would be enormous.

Congress recognized this threat, and in the 1998 Spaceguard Survey tasked NASA with finding and tracking 90% of the estimated total of near-Earth objects 0.6 miles (1 kilometer) in diameter or larger within 10 year. NASA exceeded the 90% goal in 2011.

In 2005, Congress passed another bill requiring NASA to expand its research and track at least 90% of all near-Earth objects 460 feet (140 meters) or larger by the end of 2020. This year passed and, mainly due to lack of financial means, only 40% of these objects have been mapped.

As of September 18, 2022, astronomers have located 29,724 near-Earth asteroids, of which 10,189 were 460 feet (140 meters) or larger in diameter and 855 were at least 0.6 miles (1 kilometer) in diameter. Around 30 new items are added every week.

A new mission funded by Congress in 2018 is scheduled for 2026 to launch an infrared space 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 so-called “city killer” asteroid the size of a football field passed within 45,000 miles (72,420 kilometers) of Earth in 2019. A jet-sized asteroid 747 sw is approached in 2021, as is a 0.6 mile (1 kilometer) wide asteroid in 2012. Each was only discovered about a day before passing Earth.

Research suggests Earth’s rotation creates a blind spot, hiding some asteroids from detection or making them appear motionless. 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.

The recent discovery of a 1.2 mile (2 kilometer) diameter asteroid suggests that there are still large hidden objects.

A huge crater in the desert.
This crater near Flagstaff, Arizona was created when an asteroid estimated to be 160 feet (50 meters) in diameter crashed into Earth around 50,000 years ago.
USGS/D. Roddy via Wikimedia Commons

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.

The DART mission will be the first-ever attempt to deflect a large asteroid. But it won’t be the first time humanity has sent something to an asteroid. NASA’s Deep Space Impact mission crashed a probe into Comet 9P/Tempel in 2005 to take scientific measurements of the comet, and in 2018 Japan’s Hayabusa2 mission collected samples from asteroid Ryugu and brought them back on Earth, but none of these were designed as a test of planetary defense.

The DART mission should generate a lot of useful information. This data will come from a camera on board the DART spacecraft which will send images back to Earth until the moment of impact. Additionally, a tiny satellite called LICIACube which was deployed from DART on September 11, 2022, will take photos of the impact. A European Space Agency follow-up mission, called Hera, will launch in 2024 and rendezvous with Didymos in 2026 to begin collecting data.

Planetary Defense Spending

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

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 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.

This is an updated version of a story originally published on March 1, 2022.