On September 26th at 7:14 pm (local time), NASA’s ‘DART’ mission will begin in earnest. It is the task of changing the orbit of the spaceship ‘DART’ and the asteroid Dimorphus when it collides. If even a small asteroid collides with Earth, most living things, including humans, could become extinct. To prevent this, the National Aeronautics and Space Administration (NASA) launched a spacecraft dart on November 23, last year. How far will the darts that arrive at their destination after a 10-month voyage push away the asteroid?
2100 Potential Earth Threat Asteroids
In fact, asteroids are still falling to Earth every day. According to NASA, about 5 million asteroids and comets collide as they pass around the Earth every day. However, due to their small size, they collide with the Earth’s atmosphere and most of them burn away. Asteroids that are within about 7.5 million km from Earth and have a diameter of 150 m or larger are classified as ‘potential Earth threat asteroids’ and monitored.
Asteroids are clustered in the asteroid belt between Mars and Jupiter, but are spread throughout the solar system. So far, scientists have discovered about 26,000 asteroids that are close to Earth. A near-Earth asteroid is an asteroid that approaches Earth’s orbit and has the potential to collide with the Earth. Of the 26,000, about 2,100 were classified as potential Earth-threatening asteroids. If an asteroid with a diameter of 300 m or more collides with the Earth, one continent can be destroyed. Also, if an asteroid of 1km falls on Earth, the entire climate of the Earth could change. When an asteroid lands on Earth, it produces a huge amount of dust, which doesn’t disappear for years, blocks sunlight and changes the climate.
NASA’s Dart mission is the first human experiment to change the orbit of an asteroid that could threaten Earth in the future. Dart is an acronym for ‘Double Asteroid Redirection Test’. Dart’s destination is Dimorphos, a moon of the near-Earth asteroid Didymos. Didymos means twins in Greek. It got its name because it has the moon Dimorphus with a diameter of 163 m.
The Dart spacecraft is a small spaceship the size of a small car (about 500 kg). However, it collides with the asteroid at a speed of 6.6 km/s. In that case, NASA believes that Dimorphus’ orbit will move inward and the orbital time of 11 hours and 55 minutes will be shortened by several minutes. Even a slight shift in orbit could avoid a collision because it would avoid the Earth. The total cost of the Dart spacecraft was $325 million (about 400 billion won).
But why did NASA target Dimorphos among so many asteroids? This is because Dimorphus is located at a reasonable distance from the Earth and small in size, making it relatively easy to correct orbit. In addition, even if the spacecraft and Dimorphus collide by mistake, the satellite Dimorphus is bound by the gravity of Didymos (780m in diameter) and there is no possibility of colliding with the Earth, so it is safe. In particular, Didymos passes close to the Earth when orbiting the Sun. By the end of September this year, when it collides with the spacecraft Dart, it will pass a relatively close distance of about 10.8 million km from the Earth, so even with a ground telescope, the orbital change as a result of the collision. NASA explains that it has the advantage of being able to observe
Recently, NASA confirmed that Didymos’ orbit was perfectly aligned with the Dart spacecraft through the Lowell Observatory’s 4.3m telescope in the United States. The collision process between Dart and Dimorphus is recorded and transmitted to Earth by the Italian space agency’s small satellite ‘Liciacube’, which was launched together. Also, from the ground, NASA will broadcast the process live through its TV channels, websites, and social media accounts from 6 pm on September 26, about an hour before the collision.
The Dart team will calculate the altered asteroid orbit by analyzing the images of Lysia Cube and data observed with ground telescopes. Precise data is required because this experiment has to analyze the changes by dividing them into before and after the collision. In 2024, the European Space Agency (ESA) plans to launch the Hera probe to investigate the exact mass and internal structure of Dimorphus, changes in its orbit, and the size and shape of the crater left by the impact.
It is possible to prevent the 2182 ‘Benu’ collision
If the dart test is successful, NASA plans to apply the method to ‘Earth-threatening asteroids’ that will come to Earth in the future. In particular, NASA plans to prevent the asteroid ‘Benu’, which is likely to collide with Earth. Discovered in 1999, Benu with a diameter of about 490 m has been confirmed to collide with Earth in 2182 with a probability of 1 in 2700. To prepare for this, NASA is preparing a spacecraft ‘Hammer’ that will change its orbit. In addition, it is planning to build a space telescope ‘Nio Surveyor’ that can monitor up to two-thirds of unidentified small asteroids within 48 million km of the Earth and launch it in 2026.
An asteroid that knows its orbit in advance like ‘Benu’ can correct its orbit by launching a spacecraft like this. Scientists are also researching ways to correct orbit by mobilizing several artificial satellites close to the asteroid and pulling the asteroid with gravity. On the other hand, what to do if an undiscovered asteroid suddenly appears and a collision is imminent? According to NASA, many large asteroids (1.6 km or larger) close to Earth are located, but only 40% of small asteroids (10 to 140 m in diameter) are known. Thus, small asteroids may come close to Earth without our knowledge. In this case, NASA explains, the last resort would be to fire a nuclear bomb from Earth to destroy the asteroid.
The method shown in the 1998 disaster movie ‘Armageddon’ is to use a nuclear bomb to shatter an asteroid to reduce the impact on the Earth. In the real world, a team from Johns Hopkins University in the United States, Dr. Patrick King, has proposed a method to set up a nuclear bomb on a huge asteroid rushing to Earth and detonate it. A supercomputer conducted a virtual experiment in which a 1 megaton-class nuclear bomb was fired from the Earth and detonated into an asteroid with a diameter of 100 m, and the result was found that the asteroid shattered and deviated 99.9% of the Earth. It has been proven that nuclear bombs can prevent asteroid impacts. However, if a nuclear weapon is detonated to detonate an asteroid, there is a possibility that small radioactive fragments will be poured into the Earth’s atmosphere, so we are looking for a better way.
NASA hopes that on September 26, the Dart spacecraft will orbit even a few centimeters to secure the technology to defend the Earth. NASA thinks that if it is possible to perfectly correct the orbits of asteroids through this, it will be possible to modify the orbits of asteroids around the Earth to match human intentions.