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Asteroids and their Relationship to the Earth

2020-04-16 来源: 51Due教员组 类别: Report范文

下面为大家整理一篇优秀的paper代写范文Asteroids and their Relationship to the Earth ,供大家参考学习。这篇论文讨论了小行星及其与地球的关系

小行星是太阳系中的物体,类似于行星体并绕太阳运行,但比大多数行星要小得多,质量也要小。他们与地球有着密不可分的关系。本文首先介绍了小行星的形成,一般情况和分类,并锁定了近地小行星(NEA)作为研究它们与地球关系的主要研究对象。它还讨论了小行星对地球的撞击并指出了威胁和后果。接下来,本文研究小行星的观测,轨道计算和防御方法,以及未来小行星资源的潜在利用。

 

Asteroids and their Relationship to the Earth

Asteroids are objects in the solar system, which resemble planetary bodies and orbit the Sun, but are much smaller and less massive than most planets. They have an inseparable relationship with the Earth. This paper first introduces the formation and the general situation and classification of asteroids, and them locks the near-earth asteroids (NEAs) as the main research subject to study their relationship with the Earth. It also discusses the asteroid impacts on the Earth and points out the threats and consequences. Next, this paper investigates the observation, orbit calculation, and defenses methods on asteroids, as well as the potential use of the resources on asteroids in the future.

The Formation of Asteroids

Initially, astronomers thought that an asteroid was a rupture of a planet between Mars and Jupiter; however, the combined mass of all asteroids in the asteroid belt was even lower than the mass of the Moon. Today, astronomers believe that asteroids are the remnants of a planet that are not formed during the formation of the solar system. Jupiter, the fastest growing mass in the solar system, prevents the formation of another planet in today's asteroid belt. The orbit of asteroids in the asteroid belt is interrupted by Jupiter, and they constantly collide and crumble. Other substances were driven out of their orbit and start colliding with other planets. Large asteroids heat up after they are formed due to the decay of the aluminum radioisotope 26AI (and possibly the iron radioisotope 60Fe). Heavy elements such as Ni and Fe subside to the interior of the asteroid in this case, while light elements such as Si floats up. This process resulting in the separation of internal asteroid material, and the composition of the new asteroid resulting from subsequent collisions and fractures is therefore different. Some of these fragments later fell to the Earth as meteorites.

 

(Pearson Education, 2007)

The asteroid belt is an asteroid-dense area in the solar system that lies between the Mars and Jupiter's orbit, as counted by the already numbered 120,437 asteroids, where 98.5% of asteroids are found. Since the asteroid belt is the most densely populated area of asteroids estimating as many as 500,000 asteroids, this area is therefore known as the main belt. Within an area of about 2.17-3.64 AU (astronomical unit, 1 AU=149,597,870,700m) from the Sun, more than 500,000 asteroids have been gathered to form an asteroid belt. With so many asteroids coherent in the asteroid belt, Jupiter's gravity plays a bigger role than that of the sun.

Near-Earth asteroids (NEAs) refer to asteroids whose orbit intersects with the Earth’s orbit. Such asteroids may contain risks of impacts on the Earth but they are also relatively easy to detect with probes. NEAs are the focus of this paper.

Trojan asteroids are a group of small planets or moons whose orbits overlap larger ones’ orbits. This kind of asteroids is located in Jupiter's orbit, divided into two groups, and each group is separated by 60 degrees from Jupiter. Torojan asteroids, Jupiter, and the Sun constitute an equilateral triangle, and this position forms a relatively stable Lagrange point. Trojan asteroids run at the same speed as the accompanying celestial bodies, so there is no collision between the two.

NEAs and their Historical Impacts on the Earth

The orbits of NEAs are normally within 1.3 AU from the Sun and less than 0.3 AU from the Earth’s orbit. NEAs could be divided into four types according to their orbits and they have different chances to impact on the Earth:

Amor Asteroids: the perihelion is 1.02 to 1.3 AU;

Apollo Asteroids: semi-axis > 1.0 AU, the perihelion < 1.02 AU;

Aten Asteroids: semi-axis < 1.0, the aphelion > 1.0167 AU;

Atira Asteroids: the aphelion < 0.983 AU.

 

(source: google)

Amor Asteroids move across the orbit of Mars and come near the orbit of the Earth. Because of the gravitational perturbation of the large planets, the orbit of the Amor asteroids might go through the Earth's orbit and could potentially collide with the earth. Until June 2011, over 3300 asteroids were classified as Amor Asteroids, about 470 of them earned permanent numbers and 68 earned official titles. In average, 1 Amor Asteroid might impact on the Earth every billion years.

Apollo Asteroids’ orbit lies between Mars and the Earth. Some asteroids in this group have a very high orbital eccentricity and their perihelion could even reach the orbit of Venus. Until June 2011, over 4000 asteroids were classified as Apollo Asteroids, about 570 of them earned permanent numbers and 60 earned official titles. In average, 3 Apollo Asteroid might impact on the Earth every billion years.

Aten Asteroids’ orbit is generally within the Earth’s orbit. Some asteroids in this group have a high orbital eccentricity and they might intersect with the Earth’s orbit with in its orbit. Until June 2011, over 3300 asteroids were classified as Amor Asteroids, about 470 of them earned permanent numbers and 68 earned official titles. In average, 1 Amor Asteroid might impact on the Earth every 100 million years.

The orbits of NEAs are close to the Earth, especially the orbits of the Apollo Asteroids and the Aten Asteroids intersect with the Earth's orbit, resulting in a possibility of impact on the Earth. There are some examples to show the threats of the NEAs. On February 15th 2013, in Chelyabinsk, Russia, A meteor shower took place at 9.15 a.m. local time. The meteorites left an approximately 10 km long trace in the atmosphere. According to Russian media reports, 1,500 people were injured in the incident and more than 1,000 houses were damaged. On June 30th 1908, a large explosion took place in the Tunguska area of Russia and led to the destruction of about 2,000 square kilometers of Siberian forests. Many scientists consider the Tunguska Event as an asteroid impact on the Earth. Similar incidents happened in China as well. On March 8 1976, a major meteorite burst occurred over Jilin City, and the fragments spread near the outskirts of Jinlin City, Yongji County, and Jiaohe City within a radius of 500 square kilometers. It was the largest meteor shower the world had ever seen back then, 138 meteorite specimens and more than 3,000 pieces were collected. The total weight was 2615 kg and the biggest piece of meteorite weighing 1770kg, which was also the world's heaviest meteorite at that time. Its impact on the ground caused mushroom clouds of dust, and went deep in the permafrost layer, forming a 6.5 m deep, 2 m diameter pit (Peter & Hans, 2007). On November 5, 2014, a small-scale asteroid collision with the Earth also occurred in Xilin Gol League, Inner Mongolia. Jilin meteorite rain caused little damage to people, but what happened in Chelyabinsk caused many injuries and housing dimensions. If the Tunguska Event occurs in a densely populated area, the consequences will be disastrous.

Currently, more than 11,000 NEAs have been identified, of which 1,483 are considered potentially dangerous. Asteroids that are larger than 1 km in diameter impact on the Earth at energies equal to hundreds of times the nuclear bomb energy of the global nuclear arsenal, which can cause severe catastrophes in climate, ecology, and environment upon impacts on the Earth and may lead to the extinction of species. NEAs impacts on the Earth are often considered as the culmination of human civilization. Scientists analyze that the historical causes of disasters such as the extinction of dinosaurs may be the impacts of asteroids. It is now generally accepted that there is a potential risk of impacts no the Earth if the minimum distance between the asteroid’s orbit the Earth’s orbit is less than 0.05 AU. Compared with natural disasters such as earthquakes and floods, the impact of NEAs on the Earth has three characteristics. First, NEAs impact is a momental global catastrophic disaster. Second, it is possible to accurately forecast it in advance about the level and the location of the impact. Third, the NEAs impact on the Earth could be avoided. In order to prevent the threat of asteroids impact, more and more studies are currently being done on the observation and the defense of near-Earth asteroids.

Asteroids Observation, Impact Prevention, and Exploration

Grasping the number and distribution of the NEAs plays a significant and fundamental role in analyzing their threats and risks. This requires high level of observations and orbital calculations of the NEAs. As astronomical telescopes and photographic techniques have been upgraded, more and more asteroids have been discovered. Till 2014, 10,576 NEAs were discovered and 1,478 of them were discovered in that year. Till October 2015, the number raised up to 13,166. Among them, 857 asteroids were larger than 1 km in diameter and there were 1,627 asteroids might possibility impact on the Earth. Of all the discovered NEAs, about 50% are Apollo Astroids, 43% are Amor Astroids, 7% are Aten Asteroids, and only 23 are Atira Asteroids. Being authorized by International Astronomical Union (IAU), Minor Planet Center (MPC) became the organizer of the asteroids observation. The Near-Earth Object Program Office of NASA is also responsible for relevant programs of NEAs. The Near Earth Objects Dynamic Site (NEODS) located in Italy also provides orbital data and assessment of the impacts and other information.

NASA has established a Planetary Defense Coordination Office (PDCO) in 2016 to discover, track, and identify asteroids and comets that pose a potential threat to the Earth and to issue warnings of possible impacts. On June 30 2017, NASA announced a plan called Double Asteroid Redirection Test (DART) had entered the preliminary design phase from the concept exploration phase, and the completed spacecraft will hit a pair of asteroids (NASA, 2017). DART is the first technology validation project of changing the asteroid’s orbit to prevent it from impacting on the Earth. NASA is planning on launching a spacecraft to shake the orbit of a binary asteroid system, which is composed of Didymos A of about 780 meters in diameter, and Didymos B of about 160 meters in diameter and flying around Didymos A. NASA has been closely observing these two asteroids since 2003, and predicted that they will fly “far” over the Earth twice in 2022 and 2024. Lindley Johnson, PDCO officer, claimed this would be a historic experiment on a non-threatening asteroid (And one, 2017). In fact, asteroids encounter the Earth almost every day; only the vast majority of them break down into the atmosphere and burn down, making it hard to cause considerable damage. However, the larger asteroid poses a threat to the Earth. NASA considers asteroids that exceed 1 kilometer in diameter to be the potential threat to global impacts and to focus their observations and follow-ups. DART's research object is a medium-sized asteroid. Once they hit the Earth, they maybe cause regional damage, and Didymos B belong to this category.

Asteroids have been suggested for future use as a source of the Earth, such as using asteroids as mining grounds of rare material or building materials for space stations. It is cumbersome and expensive way to launch materials from the Earth to space, in the future it might be possible to establish factories on asteroids to directly manufacture and mine them. However, according to the Elvis equation developed on the basis of the Drake equation, there are only 10 asteroids in the solar system that might possess platinum group metals that worth mining.

Conclusion

The collision of celestial objects is one of the chief factors affecting the physical development and changes of the universe. It not only makes the Earth a suitable planet for life, but also may have driven many species extinct in the past, and continues to cause occasional mass devastation to this day. There are many asteroids around the Earth and their orbits overlap the Earth’s orbit. Through generations of research, people have discovered the unpredictable horror of the universe in which we are not the main characters or even guaranteed survival, but are simply guests on a wet rock, hoping no other large rocks happen to come our way.

 

 

References

 

Bobrowsky Peter & Rickman Hans. (2007). Comet/asteroid impacts and human society: an

interdisciplinary approach. Berlin, Heidelberg: Springer.

Dakin Andone. (2017). NASA unveils plan to test asteroid defense technique. CNN, July 1.

Jenifer B. Evans, Frank C. Shelly, and Grant H. Stokes. (2003). Detection and Discovery of

Near-Earth Asteroids by the LINEAR Program. Lincoln Laboratory Journal Vol. 14 No. 2.

NASA. (2017). Double Asteroid Redirection Test (DART) Mission.

https://www.nasa.gov/planetarydefense/dart

NASA (2017). Asteroid Fast Facts. Updated Aug. 4.

https://www.nasa.gov/mission_pages/asteroids/overview/fastfacts.html

Pearson Education. (2007). Chapter 9: Asteroids, Comets, and Dwarf Planets. Publishing as

Pearson Addison-Wesley.

 

 

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