The threat of asteroids and comets
Millions of cosmic bodies, such as asteroids and comets, orbit the sun and often collide with Earth. Most of these are too small to pose a threat, but some can be cause for concern. Near-Earth objects include asteroids and comets whose orbits they will take within 120 million miles (193 million kilometers) from the sun.
Astronomers consider a near-terrestrial object a threat if it wants to get within 4.6 million miles (7.4 million kilometers) from the planet and if it is at least 460 feet (140 meters) in 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 – 1 kilometer or more – can have global effects and even cause mass extinctions.
The most famous and destructive celestial impact occurred 65 million years ago when an asteroid 10 kilometers in diameter crashed on what is now the Yucatán Peninsula. It exterminated most plant and animal species on Earth, including the dinosaurs.
But smaller objects can also cause significant damage. In 1908, a celestial body about 50 meters above the sea exploded Podkamennaya Tunguska River in Siberia. It leveled more than 80 million trees across 830 square miles (2,100 square kilometers). In 2013, an asteroid just 20 meters across burst into the atmosphere 20 miles (32 kilometers) above Chelyabinsk, Russia. It released the equivalent of 30 Hiroshima bombs of energy, more than 1,100 people injured, and caused $33 million in damage.
The likely next significant-sized asteroid to potentially hit Earth is asteroid 2005 ED224. When the 164-foot (50 meters) asteroid passes by on March 11, 2023, there will be about one 1 in 500,000 chance of impact.
Looking at the sky
While the the chance that a larger cosmic body will hit the earth is smallthe destruction would be huge.
Congress recognized this threat, and in the Spaceguard Survey 1998, it instructed NASA to find and track 90% of the estimated total of near-Earth objects 0.6 miles (1 kilometer) or larger in diameter within 10 years. NASA exceeded the target of 90% in 2011.
2005, Congress has passed another bill NASA required to expand its search to track at least 90% of all near-Earth objects 140 meters or larger by the end of 2020. That year has come and gone and, mainly because of a lack of financial resourcesnothing but 40% of those objects have been mapped.
As of September 18, 2022, astronomers have 29,724 . localized asteroids near Earth, of which 10,189 are 460 feet (140 meters) or larger in diameter and 855 are at least 0.6 miles (1 kilometer) wide. About 30 new objects are added weekly.
A new mission funded by Congress in 2018 is planned in 2026 to provide an infrared space telescope—NEO Surveyor—dedicated to looking for potentially dangerous asteroids.
We can only prevent a disaster if we know it is coming, and asteroids have crept into Earth before.
A so-called city-killer asteroid the size of a football field passed by less than 45,000 miles (72,420 kilometers) from Earth in 2019. An asteroid the size of a 747 fighter jet came close in 2021, just like a asteroid 1 kilometer wide in 2012. Each of these was discovered alone about a day before it passed the Earth.
Research suggests that Earth’s rotation creates a blind spot, hiding some asteroids from detection or making them appear stationary. This can be a problem since some surprising asteroids don’t miss us. In 2008, astronomers were spotted a small asteroid just 19 hours before it crashed into rural Sudan.
The recent discovery from an asteroid 2 kilometers in diameter suggests that large objects are still lurking.
What can be done?
To protect the planet from cosmic hazards, early detection is essential. At the 2021 Planetary Defense Conference, scientists advised at least 5 to 10 years preparation time to mount a successful defense against dangerous asteroids.
When astronomers find a dangerous object, there are: four ways to mitigate disaster. The first concerns regional first aid and evacuation measures. A second approach is to direct a spacecraft to fly near a small or medium-sized asteroid; the craft’s gravity would slowly change the object’s orbit. Until change the path of a larger asteroidcan we collide with it at high speed or detonate a nearby warhead.
The DART mission will be the first-ever attempt to deflect a large asteroid. But this won’t be the first time humanity has sent something to an asteroid. NASA’s Deep Space Impact Mission a probe crashed into comet 9P/Temple in 2005 to make scientific measurements of the comet, and in 2018 Japan’s Hayabusa2 mission collected samples from the asteroid Ryugu and brought them back to earthbut neither was designed as a planetary defense test.
The DART mission should provide a lot of useful information. This data comes from a camera on board the DART spacecraft that will send images back to earth until the moment of impact. In addition, a small satellite called LICIACube deployed from DART on September 11, 2022, will capture photos of the impact. A follow-up mission from the European Space Agency, called Hera, will launch in 2024 and rendezvous with Didymos in 2026 to start collecting data.
Planetary Defense Expenses
In 2021, NASA’s planetary defense budget $158 milliononly 0.7% from NASA’s total budget and 0.02% of the approximately $700 Billion US Defense Budget.
Is this the right amount to invest in air monitoring given that some 60% of all potentially dangerous asteroids go undetected? This is an important question to ask when considering the possible consequences.
Investing in planetary defense is similar to buying homeowners insurance. The chances of experiencing an event that destroys your home are slim, but people still buy insurance.
If even a single object larger than 460 feet (140 meters) hit the planet, the destruction and loss of life would be extreme. A larger impact could literally wipe out most species on Earth. Even if such a body is not expected to touch the earth in the next 100 years, the probability is not zero. In this low probability vs high impact scenario, investing in protecting the planet from dangerous cosmic objects can bring peace of mind to humanity and prevent catastrophe.