NASA’s Double Asteroid Redirection Test (DART), successfully crashed into its asteroid target, Dimorphos on September 26, 2022. This is the world’s first planetary defence technology demonstration. NASA’s first attempt was to shift and deflect the position of an asteroid in space rather than blowing it up. Though the asteroid did not pose any threat to the Earth, it is now proved that scientists can save the Earth from being destroyed due any asteroid collision. The mission cost NASA about US$ 325 million.
NASA’s James Webb Space Telescope released an animation, which is a timelapse of images covering the time spanning before the impact through 5 hours post the impact. Similarly, the Hubble Telescope’s Wide Field Camera 3 captures images of the impact in visible light. This is for the first time that both the telescopes observed the same target at the same time. Thus, NASA confirmed October 8, 2022 that DART mission impact changed asteroid’s motion in space.
Asteroids
The leftover materials from the formation of the Sun, Earth, and other planets through the accretion and collection of gas giants and rocks are scattered as comets, asteroids, and meteoroids in the solar system. Some of them cross their paths and collide with the Earth from time to time, resulting in a spectacular meteor shower. Small rocks burn up completely in the atmosphere due to frictional heating. Most of them are hard rocks and could have masses of thousands or millions of tonnes. Charred pieces out of large rocks fall through as meteorites. The impact would be devastating if the meteorite is one or more kilometres wide.
About 66 million years ago, a 10-15 km wide asteroid, had struck the Earth. Consequently, there were tsunami, volcanic eruptions, and thick dust clouds which wiped out dinosaurs and nearly 75 per cent of all species.
Why the Need
On February 15, 2013, a meteor exploded over Chelyabinsk, Russia which created an airburst and shockwave that struck six cities across the country. This was a reminder that dangerous objects could enter Earth’s atmosphere at any time. The Chelyabinsk object was about 60 feet wide. However, it demonstrated that even small asteroids could be of concern. This incident alerted the world of making real-world tests of space-based planetary defence systems all the more important.
Though the chances for any future collision are low, the collision would be devastating if it occurs, and would wipe out the entire human civilisation. Therefore, NASA has been tracking and keeping a close watch on nearly 26,115 asteroids whose orbits are dangerously close to the Earth.
About the DART Mission
DART is a mission under NASA’s planetary defence effort as part of the Near-Earth Object (NEO) Observations Program, composed of projects to find, track, and characterise NEO’s. The mission objective is to find and track at least 90 per cent of the predicted number of NEOs that are 140 metres or larger in size, and to characterise a subset representative to the entire population. These objects pose a risk to the Earth, as there has been concern about the level of devastation, an impact like this would cause. Therefore, there should be continuous focus and global search efforts. However, there is no known asteroid larger than 140 meters in size that would hit the Earth in the next 100 years.
The Johns Hopkins Applied Physics Laboratory (APL) has built DART and the spacecraft’s single instrument, the Didymos Reconnaissance and Asteroid Camera for Optical (DRACO) navigation for NASA. DRACO has been designed not only to capture images of Didymos and Dimorphos, but also support autonomous optical navigation for the DART spacecraft. Another camera, a Light Italian CubeSat for Imaging of Asteroids (LICIACube), also took a piggy back ride with the DART. Weighed about 600 kg, DART is the first-ever mission dedicated to investigating and demonstrating a method of asteroid deflection in space through kinetic impact.
The DART spacecraft was launched by a SpaceX rocket on November 24, 2021. In this mission, DART was deliberately made to collide with a target asteroid. The targeted asteroid, Dimorphos, is actually a moon to a slightly larger asteroid, called Didymos. The collision with the target asteroid changed its speed and path. While Didymos is 780 meters at its widest, Dimorphos is about 160 meters. Dimorphos orbits around Didymos, and the two-body system goes around the Sun.
Technique and Impact of the Test
NASA undertook the ‘kick’ technique to shift and deflect the space rock Dimorphos, which orbits around Didymos, the primary asteroid. NASA’s objective was to change its trajectory instead of destroying it. The DART travelled at a speed of 23,760 km per hour, and the momentum was adequate to slash the angular momentum of Dimorphos, making it speed up and move closer to Didymos.
This action of DART has reduced the orbital period and the time taken for the Dimorphos to go around Didymos. Thus, the DART deflected the trajectory of the pair of rocks. A small shift could be enough to knock a similar object off its collision course with the Earth.
Hovering at 50 km from the asteroid, the two cameras—DRACO and LICIACube aboard the CubeSat captured the plume of the debris ejected by the collision. At 11 million kilometres, both the asteroids Dimorphos and Didymos appeared like a blip of dot even through the best of telescopes. As Dimorphos and Didymos revolve around each other once in 11 hours and 55 minutes, the total brightness of the pair darkens when Dimorphos passed in front of and behind Didymos.
Now, the astronomers are spending time in observing the periodic change in the brightness, using the telescopes, to tease out the altered orbital period. All this data is still in process and would help fine-tune the technology. Several factors are to be considered, including the size, mass, composition, nature of orbit, and the probability of a collision with Earth. The DART mission has opened avenues for these kinds of studies which is just the beginning of the effort to set up a planetary defence system.
After NASA, China is planning to deflect a 40-m diameter Earth-crossing asteroid, named 2020 PN1, sometime in 2026. The intentions and purpose behind this mission may be the lure of space mining. Apparently, it looks like protecting the Earth from killer asteroids, but the lure of space mining lurks behind.
Other Possibilities Space mining could be economically viable with the passage of time. Countries may try to pull a mineral-rich asteroid near the Moon or establish a space mining factory between the orbits of Earth and Mars to source precious mineral resources. Initially, NASA had planned to bring a 20-tonne space rock near to Earth to study and mine in its Asteroid Redirect Mission (ARM), but the mission has been postponed for the time being.
The future pertains to green energy technologies based on low-carbon economy with electric vehicles, solar panels, wind turbines, and energy storage devices. For this purpose, rare Earth elements such as yttrium, niobium, rhodium, palladium, osmium, iridium, and scandium are critical. They are short in supply for now, and asteroid mining is believed to solve this problem.
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