In October this year, the first National Planetary Defense Conference was held in Guilin.
At the Planetary Defense Conference, many people's first reaction when they saw this domineering name was to look confused, and it was as if they had mistakenly entered the three-body world. Didn't the earth receive the threat of the three-body? Water droplets are also on their way? But looking at this grounded conference photo, how to look at it is not like that.
Rest assured, The Earth has not yet been threatened by any real outer space. But that doesn't mean earth is always safe, and the topic of planetary defense, while magical, is actually closely related to our lives. The biggest threat we face from outer space is the impact of a near-Earth asteroid.
Exploring the risk of near-Earth asteroid impacts and how to address them was the theme of the conference.
Near-Earth asteroids pose a threat to Earth
It seems distant but close
About 4.6 billion years ago, collisions in the early formation of the solar system left many rocky debris, and these ancient space rubbles are asteroids. Currently, the number of known asteroids exceeds 1.1 million. The largest asteroids can go up to 530 kilometers in diameter, such as Vesta, and the smallest diameter is only a few meters.
Most of these asteroids exist in the main asteroid belt between Mars and Jupiter. It is estimated that the main asteroid belt contains 1.9 million asteroids larger than 1 km in diameter, as well as millions of smaller planets. According to the orbital distribution of asteroids (perihelion distance, aphelion distance, major semi-axis), it can be divided into four major families: Amor, Apollo, Aten, and Atira.
Figure/ Schematic map of the orbital distribution of NASA JPL populations of Sun, Earth, and near-Earth asteroid populations
Jupiter's huge gravitational force will change the asteroid's original orbit, coupled with the gravitational pull of other celestial bodies, solar wind, solar radiation and other complex space environment effects, the asteroid may leave the main asteroid belt, fly into the long space, become a "wandering asteroid".
Some "wandering asteroids" have paths that intersect the Earth's orbit, and in general, asteroids within 45 million kilometers of the Earth's orbit are called near-Earth asteroids (NEAs).
A little closer, an asteroid 7.5 million kilometers (0.05 astronomical units) from Earth and greater than 140 meters in diameter is considered a potentially dangerous asteroid (PHA) that could cause significant damage to Earth.
Figure/Orbit of a potentially dangerous asteroid (PHA) known nasa data in 2013
As of this year, there are nearly 28,000 near-Earth asteroids discovered by telescopes, and this data is growing at a rate of 3,000 per year. Near-Earth asteroid flyby events observed this year alone have occurred 1,074 times, and 21 asteroids have even flown into the atmosphere.
Asteroids if they hit Earth
What happens?
After entering the atmosphere, high-speed asteroids will explode and disintegrate under the interaction of ultra-high-speed aerodynamic and aerothermal interactions, which is what we often call "fire meteors". The debris after the disintegration of the asteroid hits the surface of the Earth, and the shock wave and kinetic energy generated by the impact are extremely destructive to the Earth.
Photo/ Manicouagan impact crater in Quebec, Canada
If the impact on the earth's surface will cause serious casualties and property damage, even if it falls into no man's land, in addition to damaging the surface to form craters, the shock waves, thermal radiation and light radiation generated by the impact may also cause forest fires. The various materials produced by the impact will fill the entire atmosphere, blocking the sunlight and triggering the ice chamber effect or the greenhouse effect.
If hit by the ocean, the shock wave triggers a tsunami. It has been recorded that an asteroid called "Eltain", with a diameter of 4 km, struck the bottom of the South Pacific Ocean, causing a tsunami of 200 to 300 m in the sea at an altitude of 1,200 to 1,500 km.
Figure/Classification of asteroid impact events
According to research estimates, there have been 22 extinctions of varying degrees in Earth's history, 11 of which have been related to asteroid impacts. For example, regarding the extinction of dinosaurs, the scientific community generally believes that it was caused by the impact of an asteroid with a diameter of about 10 kilometers.
There was also the Russian meteorite fall in February 2013, when an asteroid about 18 meters in diameter and with a mass of nearly 10,000 tons exploded over Chelyabinsk, Russia, generating an energy of about 500,000 tons of TNT, equivalent to 30 Hiroshima atomic bombs. The incident left more than 1,500 people injured.
Photo/Chelyabinsk incident
Face an asteroid attack
What can humans do?
In the face of such a powerful "celestial alien", what can human beings do to deal with it? Scientists have thought of a few tricks.
The first trick: know thyself and know the other, never lose a battle
In order to avoid the "people sitting at home, the stars come from the sky" hand-wringing, detection and early warning work is the top priority. Optical, radar and other ground-based telescopes can be used in conjunction with space-based telescopes to track and observe anomalous asteroids to assess whether they pose a threat to humans.
Photo/ China's main observation stations and equipment
Continuous observations of the position, orbital motion and characteristics of near-Earth asteroids with the threat of impacting the Earth are made to determine more precise possible impact locations and effects in order to make the next response. That's what the International Asteroid Warning Network is doing.
To improve its ability to respond to asteroid impacts, NASA conducts "asteroid impact exercises" every two years to simulate impact scenarios and discuss best courses of action for disaster mitigation. In the sixth planetary defense simulation exercise in 2019, Earth sent kinetic energy impactors to hit the asteroid, and the fragments of the asteroid's split hit New York, flattening more than a dozen kilometers around it.
Second move: hardcore destruction
This trick is simply to intercept and destroy the asteroid, such as by nuclear explosion. Scientists once made a calculation that using a 100,000-ton nuclear warhead, it could crush an asteroid with a diameter of hundreds of meters. It's just that a nuclear explosion can cause nuclear contamination, and the debris from the explosion may also cause other safety problems, which is risky of self-defeating.
Third trick: impact persuasion
This trick is also called kinetic energy impact redirection technology, which affects and changes the asteroid's direction and orbit through kinetic energy impact.
On November 24, NASA conducted a "double asteroid redirection test." They launched a spacecraft, DART, a small satellite called Dimorphos, to dart, which orbits the planet Didymos.
After a year of flight, DART is expected to hit Dimorphos in September 2022, and scientists predict that after a successful impact, Dimorphos's orbit will change accordingly.
Photo/ NASA Double Asteroid Redirect test DART
Trick four: heat propulsion
As the asteroid rotates, solar thermal radiation heats one side, and when it rotates to the negative side to cool, infrared energy is released, creating a tiny but sustained thrust on the asteroid, called the Yarkovsky effect.
Using this effect, it was hypothesized that if the asteroid side was blackened, it would be possible to cause the asteroid to deviate its path through thermal energy.
Fifth move: gravity traction
Launch a giant spacecraft to fly close to the asteroid, changing the asteroid's orbit through the spacecraft's gravity.
In addition to these five moves, it is envisaged to deploy solar-high-energy laser arrays in Earth's orbit to "wipe out" asteroids with lasers or, like wandering Earths, to use boosters to move asteroids.
To sum up, there are many ways for people to deal with asteroids, some of which are very large, but the actual operation possibility is very small. At present, kinetic energy impact redirection technology is the most mature one.
We often see a negotiable object such as an asteroid or comet passing by the Earth in the news, and it is rare to hear of an impact and have a devastating effect, which always makes people mistakenly think that a NEOs hitting the Earth is an unlikely thing.
In fact, the work of defending the earth has been ongoing.
End
bibliography:
[1]https://solarsystem.nasa.gov/asteroids-comets-and-meteors/asteroids/in-depth/#many_shapes_and_sizes_otp
[2]https://cneos.jpl.nasa.gov/about/neo_groups.html
[3]https://www.jpl.nasa.gov/images/pia17041-orbits-of-potentially-hazardous-asteroids-phas
[4] Ouyang Ziyuan, Running Between Heaven and Earth: Ouyang Ziyuan Science Anthology, Science Press
[5] Analysis of the impact of the small line starry sky burst and suggestions for coping with it_Wang Qixi
[6]https://www.jpl.nasa.gov/news/nasa-fema-international-partners-plan-asteroid-impact-exercise
[7]https://www.minorplanetcenter.net/
[8]https://www.nasa.gov/specials/pdco/index.html#dart
[9]https://www.jpl.nasa.gov/news/nasas-next-generation-asteroid-impact-monitoring-system-goes-online
Note: The cover art and the illustrations in the text are from the network of sources
The reproduced content represents the views of the author only
Does not represent the position of the Institute of Physics, Chinese Academy of Sciences
Source: Science Park
Edit: Fun Superman