The art concept art above depicts NASA's DART spacecraft and the Italian Space Agency's (ASI) Light Italian Cubesat for Imaging of Asteroids (LICIACube) before they hit the Didymos binary system.
Image credit: NASA/Johns Hopkins University Applied Physics Laboratory (APL)/Steve Gribben
Above our heads, a spacecraft the size of a golf cart was heading toward an asteroid that NASA instructed to crash into, with the aim of derailing the asteroid slightly from its original orbit. The purpose of this test mission is to prove that humanity is technologically prepared in case future asteroids that would really threaten Earth are detected.
On November 23, 2021, the Double Asteroid Redirection Test (DART) was launched aboard the SpaceX Falcon 9 launch vehicle from Space Launch Complex 4 East at vandenberg Space Force Base, California. The target asteroid system will be reached between September 26 and October 1 this year.
The DART mission will travel to the asteroid Didymos, which is an Amor-type near-Earth asteroids. Every 12 hours, Didymos is orbited by a mini-satellite, Dimorphos, a twin star about 160 meters in diameter that datt hits.
Will the asteroid's impact on Earth pose an extinction threat to humanity?
Will the asteroid in the disaster movie hit the Earth, causing an extinction event similar to the one that destroyed the dinosaurs millions of years ago, and will it happen now?
In fact, Earth is often bombarded by asteroids, and almost all asteroids ranging in diameter from 1 to 20 meters disintegrate in the atmosphere, so they usually do not cause harm to life on Earth.
There is an inverse relationship between the size of these objects and the frequency of impact events, which means that we are hit more frequently by small bodies than larger bodies, and this is simply because there are more small bodies in space.
Asteroid impact: The yellow dots represent the daytime impact and the blue points represent the nighttime impact; the size of each point is proportional to the light radiation energy of the impact.
Image source: NASA Jet Propulsion Laboratory (JPL)
Picture Chinese: Wow
On average, every 500,000 years, an asteroid with a diameter of 1 kilometer hit Earth, and the scientific community believes that the most recent impact of this magnitude was left at Tenoumer Crater, about 1.9 kilometers in diameter, in Mauritania, in what is now the western Sahara Desert in Africa, 20,000 years ago. An asteroid about 5 kilometers in diameter hits Earth about once every 20 million years.
The protagonist of the 2013 Chelyabinsk meteoroid impact, estimated to be about 20 meters in diameter, damaged buildings in six Russian cities and injured about 1,500 people.
Assess the risks
NASA launched the DART mission because of the threat of a major asteroid hitting Earth in the future and our fear of it.
The Torino scale is a set of indicators that measure the risk of near-Earth objects (NEO, including asteroids and comets) hitting the Earth, and evaluate the severity of the impact by integrating the probability of impact and the destructive force to obtain a numerical value. It uses integer scales from to 10, where "0" indicates that the chances of the celestial body hitting the Earth are minimal, and "10" indicates that the impact is a thousand and one shots, and the celestial body is large enough to cause a global catastrophe.
The Chicxulub impact is often thought to have been the main cause of the Cretaceous-Paleogene non-avian extinction event, with a Dühring Hazard Index of 10; the Dühringer Crater, formed about 50,000 years ago, and the Tunguska event of 1908 correspond to a Dühring Hazard Index of 8.
As online news and personal filming capabilities improve, those "thrilling" asteroids continue to test the public's fear ceiling. Currently, NASA is keeping a close eye on the asteroid Bennu, which is currently the object with the highest "cumulative danger level." (For more planetary defense monitoring, visit sentinel systems at NASA's Center for Near-Earth Object Research at NASA's Jet Propulsion Laboratory:https://cneos.jpl.nasa.gov/sentry/.)
Bennu is 500 meters in diameter and is capable of knocking out a 5-kilometer-diameter crater on Earth. However, NASA says there is a 99.943 percent chance that Bennu will pass us by.
Prepare for impact
In the orbit of Didymos and Dimorphos around the Sun, there is a point about 5.9 million kilometers from Earth. That distance is farther than our moon to Earth, but astronomically speaking, they will be very close to Earth, so DART will hit Dimorphos at this point.
DART will spend about 10 months traveling to Didymos, and as it gets closer it will slightly reorient, hitting Dimorphos at a speed of about 6.6 km/s.
Infographic of the impact of DART's impact on Dimorphos on its orbit.
Image credit: NASA/Johns Hopkins University Applied Physics Laboratory
The larger Didymos are about 780 meters in diameter and are a better target for DART. Once DART detects twin star Dimorphos, which is only 160 meters in diameter, it can make a last-minute heading correction and collide with the smaller satellites in the system.
The mass of Dimorphos is about 4.8 million tons, and the mass of DART is about 550 kg. When the spacecraft crashed into Dimorphos at 6.6 km/s, DART was able to transfer enormous momentum to Dimorphos to the extent expected to actually alter the orbit of small satellites around Didymos.
Ground-based telescopes will detect this change in weeks or months, to a degree of about 1 percent. While this may not seem like a big change, 1% is actually a very successful change, and if DART hit an isolated asteroid, its orbital period around the Sun might only change by about 0.000006%, which will take many, many years to detect.
As a result, we will be able to detect this 1% change from Earth, while the pair of asteroids will continue to orbit around the Sun. DART will also drop a small satellite 10 days before the impact to record data on the impact.
This is NASA's first mission dedicated to demonstrating planetary defense technology, and its cost is $330 million (about 2.09 billion yuan), which is relatively inexpensive in space missions, compared with the James Webb space telescope launched at the end of 2021, which cost nearly $10 billion (about 68 billion yuan).
Dart's impact produces little debris, and if you use an analogy like a similar event on Earth, it is equivalent to a train stopping on a railroad track without braking, when another train pulls over and collides with it. The two trains will not go their separate ways or destroy each other, but will sail away together: the originally stationary train will gain a certain speed, while the train that hits it will lose a certain speed; the two trains will combine into a new system, and the speed of the new system will be different from the speed of the previous two trains.
As a result, we won't feel any shock, fluctuation, or scattered debris from the DART mission.
NASA's first planetary defense mission, DART, aims to test and validate ways to protect Earth in the event of an asteroid impact threat. The DART mission will change the orbit of an asteroid through kinetic energy impacts.
Video credit: NASA/Johns Hopkins University Applied Physics Laboratory/Steve Griben/Jessica Tozer
Is it really worth the attempt?
The results of this mission will tell us how much mass and speed it takes to hit an asteroid that could pose a threat in the future. We've tracked the vast majority of asteroids closer to Earth, so we can give early warning to all of these types of objects.
That is to say, in the past we have missed some NEO events. In October 2021, the asteroid UA_1 flew over Antarctica at about 3,047 kilometers above the Earth's surface, and we were unable to detect it in advance because it flew in the direction of the Sun. The asteroid UA_1 is only 1 meter in diameter and will not cause much damage to The Earth, but we should have detected its arrival in advance.
It is very difficult to establish a deflection response system for a possible major asteroid threat, and we must act quickly to hit the target asteroid very precisely.
There is currently a candidate for such a response system, a new technology developed by the American space technology startup SpinLaunch, which can quickly send satellites into orbit, and the device can also be used to launch a certain mass spacecraft to asteroids that pass by close.
Original Author:
Gail Iles
Senior Lecturer in Physics, RMIT University, Australia
References:
[1] https://theconversation.com/could-we-really-deflect-an-asteroid-heading-for-earth-an-expert-explains-nasas-latest-dart-mission-172603
[2] https://www.nasa.gov/feature/nasa-s-first-planetary-defense-technology-demonstration-to-collide-with-asteroid-in-2022
[3] https://dart.jhuapl.edu/Gallery/