NASA is crashing a spacecraft into an asteroid to test a plan that could one day save Earth from catastrophe


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

The large binary asteroid Didymos and its small moon Dimorphos do not currently pose a threat to Earth. NASA will complete the world’s first full-scale planetary defense mission as a proof of concept. This mission is called the Double Asteroid Redirection Test, or DART.

I’m a scientist working on space and international security, and it’s my job to ask how likely it really is that an object crashes onto the planet – and whether governments are spending enough money to prevent such an event .

Finding answers to these questions requires knowing what near-Earth objects are out there. To date, NASA has only tracked an estimated 40% of the larger ones. Surprising asteroids have visited Earth in the past and no doubt will continue to do so in the future. Experiments like the DART mission can help prepare humanity for such an event.

A diagram showing thousands of blue orbits that intersect with Earth's orbit.
The orbits of thousands of asteroids (in blue) intersect with the orbits of planets (in white), including Earth.
NASA/JPL

The threat of asteroids and comets

Millions of cosmic bodies, such as asteroids and comets, orbit the sun and often crash to earth. Most of these are too small to pose a threat, but some can be a cause for concern. Near-Earth objects include asteroids and comets, whose orbits will take them within 120 million miles (193 million kilometers) of the Sun.

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

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The most famous and destructive impact in the sky occurred 65 million years ago when an asteroid 10 kilometers in diameter slammed into what is now the Yucatán Peninsula. It wiped out most plant and animal species on earth, including dinosaurs.

But even smaller objects can cause significant damage. In 1908, a celestial body about 50 meters high exploded over the Podkamennaya Tunguska River in Siberia. It has leveled more than 80 million trees over an area of ​​830 square miles (2,100 square kilometers). In 2013, an asteroid just 20 meters in diameter exploded in the atmosphere 20 miles (32 kilometers) over Chelyabinsk, Russia. It released the energy of 30 Hiroshima bombs, injuring over 1,100 people and causing $33 million in damage.

The next likely asteroid of any size to potentially impact Earth is Asteroid 2005 ED224. When the 50-meter (164-foot) asteroid passes on March 11, 2023, it has an impact probability of about 1 in 500,000.

watch the sky

While the chances of a major cosmic body hitting Earth are slim, the devastation would be enormous.

Recognizing this threat, Congress mandated NASA in the 1998 Spaceguard Survey to find and track 90% of the estimated total number of near-Earth objects 0.6 miles (1 kilometer) in diameter or larger within 10 years. NASA exceeded the 90 percent target in 2011.

In 2005, Congress passed another law requiring NASA to expand its search and track at least 90% of all near-Earth objects 460 feet (140 meters) or larger in size by the end of 2020. This year is over and mainly due to lack of financial resources 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 are 460 feet (140 meters) in diameter or larger and 855 are at least 0.6 miles (1 kilometer) in diameter. About 30 new objects are added every week.

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A new mission funded by Congress in 2018 is scheduled to launch a space-based infrared telescope – NEO Surveyor – in 2026, 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 catastrophe if we know it’s coming, and asteroids have crept onto Earth before.

A so-called “city-killer” asteroid the size of a soccer field passed less than 45,000 miles (72,420 kilometers) from Earth in 2019. An asteroid the size of a 747 jet came close in 2021, as did an asteroid 0.6 miles (1 kilometer) wide in 2012. Each of these were spotted just about a day before passing Earth.

Research suggests that the Earth’s rotation creates a blind spot that hides some asteroids from detection or makes them appear stationary. This can be a problem as some surprise asteroids don’t miss us. In 2008, astronomers spotted a small asteroid just 19 hours before it struck rural Sudan.

The recent discovery of an asteroid 2 kilometers in diameter suggests that large objects are still lurking.

A huge crater in the desert.
This crater near Flagstaff, Arizona, was formed when an asteroid estimated to be 50 meters in diameter crashed to Earth about 50,000 years ago.
USGS/D. Roddy via Wikimedia Commons

what can be done

To protect the planet from cosmic dangers, early detection is crucial. At the 2021 Planetary Defense Conference, scientists recommended at least five to 10 years of preparation time to build a successful defense against dangerous asteroids.

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

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The DART mission will be the first-ever attempt to deflect a large asteroid. But this won’t be the first time mankind has sent something to an asteroid. NASA’s Deep Space Impact mission dropped 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 to Earth, but none of them were like that designed a planetary defense test.

The DART mission should generate a lot of useful information. This data comes from a camera on board the DART spacecraft, which sends images back to Earth up to the point of impact. In addition, a tiny satellite called LICIACube, deployed from DART on September 11, 2022, will take photos of the impact. A follow-up European Space Agency mission called Hera will launch in 2024 and meet with Didymos in 2026 to begin data collection.

Expenditure on defending the planet

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 defense budget.

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

Investing in defending the planet is like buying home insurance. The likelihood of experiencing an event that destroys your home is slim, but people still buy insurance.

If even a single object larger than 140 meters hits 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 chance is not zero. In this low probability, high consequence scenario, investing in protecting the planet from dangerous cosmic objects could give humanity some peace of mind and prevent catastrophe.

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



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