Near Earth Asteroids (NEAs)RuntimeApproaching the EarthOrbitalasteroid。[7]This type of asteroid may be in danger of collision with the Earth.As of September 2011, about 19500 NEAs of medium size have been found.There are more than 500 asteroids with a diameter of more than 1 km.Once any of these asteroids hits the Earth, it will bring a devastating disaster.Near Earth asteroids are divided into Amors, Apollo, Atens and Atiras.In fact, the delta-v required to visit near Earth asteroids is smaller than that to visit the moon,NASAThe Near Earth Asteroid Date Explorer has visited 433, the most famous of these asteroids（Eros），JapanOfFalconAlso successfully landedShikawa asteroid, has now returned and brought back material samples.
Known size 4km near groundasteroidThere are hundreds of them.There may also be thousands of near Earth asteroids with a diameter of more than 1km, the number of which is estimated to be more than 2000. Astronomers believe that they can only exist in orbit for 10 to 100 million years, and they will eventuallyInner planetThe collision is either ejected when approaching the planetsolar systemThis process may consume a large number of asteroids, but it seems that the source of asteroids is still constantly replenishing.
In 1898, astronomer Victor discovered the 433 asteroid.He was startled when he calculated with his pen.The semi major diameter of the asteroid's orbit is only 1.46Astronomical unit, smaller than Mars.And when it arrivesPerihelionAt that time, it was only 1.13 AU away from the sun, which was very close to the Earth.This discovery has attracted people's special attention, and it has set up an asteroidErosA nickname for.This is the first asteroidCeresThe mainAnnular bandInner asteroid.
For more than 20 years after the discovery of the asteroid Eros, people always thought that it was the asteroid closest to the sun.However, by 1932,BelgiumAstronomer Del Porter discovered the 1221 asteroid "Amor", which set the record of the asteroid closest to the sun to 1.09 astronomical units.Only two months later, Amor's new record was replaced by another newly discovered asteroid.The asteroid suddenly set the record of near Earth distance to 0.65 astronomical units.To people's amazement, it not only crossed the earth, but also flew over the orbit of Venus.The asteroid named 1862 is called "Helios"Apollo”。
Since then, the perihelion records of asteroids have been broken one after another.According to the known data of these asteroidsPerihelionThe values of distance and track semi major diameter can be divided into three types:
Amor asteroid - Perihelion is atEarth orbitIn addition, between 1.017 and 1.3 AU, it will not threaten the earth;
Apollo asteroids - The perihelion of the orbit is less than 1 astronomical unit, so it can go deep into Venus, or evenMercuryWithin the track.
Near Earth Asteroids
These three types of asteroids are called NEO (Near Earth Object).
Near Earth asteroid Eros, occurred in January 1930Dash(When it reaches the perihelion, it is aligned with the earth and the sun).At this time, the distanceEarth distanceThe shortest is 0.17 AU, about 25 million kilometers.On May 15 of the year when Apollo was discovered, its near Earth distance was only 11.4 million kilometers.
Near Earth Asteroid Imagination
In the 1930s, NEAs frequently visited the Earth.Records show that on February 7, 1936, the asteroid Adonis passed the Earth 2.2 million kilometers away.The discovery of "Hermes" in 1937 really shocked people.On October 30 of that year, it ran to 700000 kilometers away from the earth and crossed most of the earth's sky overnight.In the eyes of astronomers, hundreds of thousands of kilometers are just around the corner.If it encounters any "misfortune" on the wayGravityFunction), maybe it will collide with the earth.HermesHermes）ForMYTHOSThe messenger of the gods is oftenZeusWait until the gods send them to the ground to "visit".People use this name to give the nearestAsteroid namingIt can't be more suitable.
Near Earth Asteroid 1999 KW4
In the following 50 or 60 years, people successively recorded near Earth asteroids andIcarusStar, geographical star, Tolo star and Austin star discovered in recent years are all close to the Earth.However, the near Earth distance of most near Earth asteroids is greater than that of the moon.That is to say, so far, no asteroid has been found flying across the earth from the earth to the moon.The frequent visits of asteroids have attracted the attention of astronomers.In recent decades, some asteroids with orbits similar to the Earth and some asteroids that may be closest to the Earth have been closely monitored by astronomers.Because some scientists believe that although the orbits of some asteroids do not completely coincide with the Earth's orbit and have a certain inclinationMegaplanetsUnder the perturbation of, the orbit will intersect the earth orbit, which may collide with the earth.This is not sensationalism and mediocrity.The International Astronomical Organization has established a monitoring and early warning agency to closely monitor and track dangerous and suspicious elements in asteroids.
In January 2022, it was learned from Zijinshan Observatory of Chinese Academy of Sciences thatNear Earth ObjectsThe telescope recently found a near Earth asteroid flying towards the earth.The International Asteroid Center numbers it2022 AAIt is expected to fly over the earth on February 4.This is also the first near Earth asteroid found worldwide in 2022.[5]
In February 2023, the Nanshan Station of Xinjiang Astronomical Observatory of the Chinese Academy of Sciences will be 1m in sizefieldOptical telescopeA near Earth asteroid was discovered for the first time.[8]
Morphological classification
Announce
edit
Imagination of near Earth asteroid impacting the Earth
Some near groundasteroidHave a highEccentric trackAs a result, they actually become "short-term" comets, because they will be completely consumed and volatilized near the sun. In fact, only a few near Earth asteroids show the same darkness as cometsCometary tail。These near Earth asteroids may come fromKuiper belt, Kuiper tookNeptuneThe periphery, where the comet came from.The rest of the near Earth asteroids may be real asteroids in Jupiter's gravityInteractionDerived fromAsteroid belt。
Two of MarsNatural satellite，PhobosAnd Phobos, which seems to be the Amor asteroid captured by the gravity of Mars.It is worth mentioning that the eccentric orbit crossing of Apollo asteroid and Aton asteroidEarth orbit, which makes it possible for them to pose the threat of collision. Amor type asteroids do not cross the Earth's orbit but may be very close to the Earth.Arjuna asteroids are sometimes used to refer to asteroids that almost completely coincide with the Earth's orbit.Near Earth asteroids are better known thanNear Earth ObjectsCome strictly.
Physical characteristics
Announce
edit
NEAsPerihelionDistance q ≤ 1.3AU, andApohelionThe distance Q ≥ 0.983AU.This group is divided into three groupssubgroupAtens, Apollo and Amors, each named after the subgroup corresponding to the first asteroid discovered.Some near Earth asteroids will be very interesting, and the speed increment required for these missions is even more thanLunar explorationThe mission is smaller, because the asteroid andEarth revolutionOfrelative velocitySmaller (△ V), andgravitational fieldWeak.These tasks may provide interesting directnessGeochemistryAnd astronomical research opportunities, and as a potential source of materials for human beings to develop the universe.This makes them attractive targets for future exploration (Xu et al., 2007).In addition, many near Earth asteroids are considered as potentially dangerous asteroids (PHAs).Potentially dangerous asteroids are currently defined according to the parameters of the possibility of asteroids heading into dangerous orbits close to the Earth.Specifically, all asteroids intersect the Earth's orbitminimum distance(MOID)Less than or equal to0.05AU andAbsolute magnitudeH=22mag,Or less, considered PHAs.In other words, any approachEarth distanceMore than 0.05AU (about 20 times more than the moon) or less than 150m in diameter (H=22mag andAlbedo0.13) are not considered PHAs.
As of May 2012, 8880 NEAs with sizes ranging from 1m to 32km have been known.The total number of near Earth asteroids with H<18 (the size is basically greater than 1km) and smaller than 7.4AU is estimated by Bottke et al. (2002) to be 960 ± 120. In a recent survey, NEOWISE (Mainzer et al., 2011), an agreement, he found 981 ± 19 NEAs with D>1km.Mainzer et al. (2011) also estimated that the total number of NEAs with diameters greater than 100m was 20500 ± 3000, slightly lower than the previous number (Rabinowitz et al., 2000; Harris, 2008).[2]
Example of impact
Announce
edit
Orbit of the First Near Earth Asteroid Discovered in China
On June 6, 2002, an estimated diameter of 10mCelestial impactThe earth.The impact occurred atmediterranean seaAt 34 ° N21 ° E.The objectatmosphereIt ignites and burns in the middle.The energy released is about (according toinfrasoundMeasurement) equivalent to 26000 tonsTrinitrotoluene(dynamite), with a mediumnuclear weaponEquivalent.India andPakistanIs inNuclear warIf the asteroid strikes the region, the consequences will be catastrophic.
On September 8, 2010, two asteroids with different orbits willUS Eastern TimeOn the morning and afternoon of the 8th, they "passed by" the earth. At that time, the shortest distance between them and the earth was less than the distance between the earth and the moon, but people on the earth could not see them with the naked eye.NASA said the first asteroid was coded2010 RX30, with a diameter of 10-20 m, will arrive at the nearest place to the earth at 5:51 a.m. EDT on the 8th, about 250000 kilometers, and its position is atNorth Pacific upper;Second code2010 RF12, 6~14m in diameter, will arrive at the nearest place to the earth at 17:12 EDT, about 80000 kilometers, when itAntarcticaupper.The average distance between the earth and the moon is about 384000 kilometers.NASAAccording to a scientist of, there are about 50 million celestial bodies passing through the space close to the Earth every day in the universe, but it is rare for these two asteroids to have such close contact with the Earth on the same day.He also said that human beings should strengthen the monitoring of celestial bodies that may threaten the EarthAstronomical telescopeIt is not large enough, and the number is not large enough, so we can only observe the "dangerous objects" flying toward the earth one or two days in advance. The "visit" of these two asteroids sounded the alarm for us.
February 15, 2013RussiaYekaterinburg Time (YEKT) 9:15 a.m. (3:15 GMT) in RussiaUrals Federal District ChelyabinskIt happened once in the cityMeteorite rainevent.When the meteorite entered the atmosphere, its diameter was about 15 meters and its mass was about 7000 metric tons. It left a track of about 10 kilometers in the sky. The main debris seemed to hitChebarkul Lake 。According to Russian media reports, 1500 people were injured in the incident.Most injuries are caused by broken glass and building vibration.Interior Ministry The spokesman said that no one was seriously injuredshock wavecauseChelyabinskThe windows of nearly 300 houses were damaged, including some hospitals, schools and kindergartens. According to the Russian Ministry of Internal Affairs, more than 1200 people have been injured, most of whom areBruise、contusionAnd scratches, etcminor woundMore than 110 slightly injured people have been hospitalized.
The Russian Ministry of Internal Affairs said that they had found falling meteorite fragments at three locations in Chelyabinsk State.One of them falls into Chebalkuli Lake, leaving aIce holeSome 1cm square black hard objects are found nearby, which are estimated to be meteorite debris.The Russian Ministry of Emergency Situations issued a warning that local residents should not approach unknown objects to avoid being carried by meteorite debrisHazardous substanceshurt.
RussiafederalAerospaceThe agency also explained that the meteorite did not predict the falling place in time when it fell. They said that because the meteorite moved irregularly after entering the atmosphere, the Russian Space Agency and foreign space monitoring and research institutions had not recorded the meteorite before, so it did not successfully track its flight path and landing siteAnalysis and prediction。In the words of the Russian Space AgencyChelyabinskIt is purely accidental.[3]
Famous Chinese scholarZhou HaizhongIn an interview with the media, the professor said that the scientific community has a variety of defense plans against near Earth asteroids hitting the Earth, and some plans are being prepared for action.The schemes with "theoretical feasibility" include:
Use nuclear weapons to blow it up, but the trouble is that the explosion is likely to turn it into many small "killers", throwing radioactive objects into unpredictable orbits;For some small near Earth objects with loose structure, the effect of explosion is limited.Moreover, if nuclear weapons explode on the surface of small bodies in the space environment, their power is weak and the effect is not ideal.This approach has been mixed.
Hit it with a spaceship, change its orbit or smash it.This method is more effective, but like the use of nuclear weapons, it may also multiply the disaster.
Apply pressure (i.e. mechanical force) to it with aircraft to accelerate or decelerate it, thus changing its flight direction.This method is ideal, but the mass of small objects that can threaten the earth is astronomical compared with that of human aircraft, which is extremely difficult to implement and has certain risks.
Use laser to make its surface material diverge outward, so as to generate reverse acceleration to change its flight direction;Or use ultra intense laser to destroy it into small pieces harmless to the earth.This method is also ideal, but it must have a high-power laser system.
Use paint to change its color, affect its absorption of sunlight and heat, and change its orbit through the change of heat energy.This method is slow to take effect, and how to transport the large amount of paint required is also a problem.
A huge kite shaped solar sail is sent to it by rocket, and the open solar sail uses the pressure generated by the rebound of solar photons to push it away from the original orbit gradually.This method is technically demanding and difficult.
Insert a device like a rocket on its surface, and let this device continuously eject material, like a jet aircraft, to change its flight direction through reaction force. Similarly, the mass of small celestial bodies that can threaten the earth is astronomical compared with that of rockets that can threaten human beings.This method seems a bit romantic.
Of course, there are other defense plans.Almost all the schemes are still at the stage of theoretical assumption;Whether they are feasible and reliable depends on future practice.
Main cases
Announce
edit
one
At 4:13 p.m. on May 2, 2014, aasteroidAnd passed the earth.The asteroid, numbered "2014 HL129", has a diameter of 67 meters and flies between the earth and the moon.The shortest distance from the earth is 300000 kilometers, which is 80000 kilometers closer to the earth and the moon."2014 HL129" is an Apollo type near Earth asteroid with an elliptical orbit, which was discovered by scientists on April 28, 2014.We passed the earth in less than a week.The shortest distance is 300000 kilometers, flying between the earth and the moon.Because it was fast enough not to hit earth.[4]
two
At more than 4:00 a.m. on May 3, 2014, the asteroid numbered "2014 GY48" flew to the Earth again.Its diameter is about 800m. If it hits the earth, the consequences will be unimaginable."Fortunately, when it flew over the earth, it was far away from the earth, about 45 times the distance between the earth and the moon."[4]
three
At about 4:00 p.m. on May 3, 2014, the asteroid numbered "2014 HO132" once again skipped the Earth, with the shortest distance of about 800000 kilometers.The asteroid is about 30 meters in diameter."2014 HL129" is the closest asteroid to the Earth in nearly half a month.It's not hostile to the earth, it's circling[3]The revolution of the sun and the return around the sun is 1.45 years.Although it is close enough to the earth, it does pose a potential threat to the earth, but it will not pose a great danger to mankind, because there is also atmospheric protection.Even if it rushes towards the earth, most materials will be burned in the atmosphere and hit the ground[4]Some are also very limited, equivalent to the power of a strong meteor shower, but from the observation, it is unlikely to hit the earth.[4]
There is a near Earth asteroid“cordon”- 7.5 million kilometers. When a near Earth asteroid crosses the "warning line", it may hit the Earth.According to statistics, asteroids with a diameter of more than 1 km hit the Earth once every 1 million years;Asteroids larger than 2km in diameter hit the Earth once every 3 million years;Asteroids larger than 6km in diameter hit the Earth for hundreds of millions of yearsPossibleonce."To take a popular analogy, the probability of an asteroid hitting the Earth is equivalent to the probability that the same person is hit twice by lightning, that is, one in 640000. You can imagine how small the probability is."[4]
Lu Jie, a former American astronaut, once pointed out that the possibility of an asteroid capable of destroying cities hitting the Earth was higher than scientists had expected earlier.It is reported that Lu Jie is a retired Chinese American astronaut who leadsNon profit organizationB612 Foundation, which studies the possibility of asteroids hitting the Earth.According to the report,a comprehensive nuclear test ban treatyOrganization collecteddata displayFrom 2000 to 2013, the global network listening to nuclear test explosions monitored 26 asteroids inEarth's atmosphereExplosion.Lujie said that one of them was 40 meters in diameter and less thanAmerican footballAn asteroid half the size of a field is enough to flatten a city.[4]
