Microbiology and Immunology 2500A/B Lecture Notes - Near-Earth Object, 1036 Ganymed, Comet Encke

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Published on 19 Apr 2013
School
Western University
Department
Microbiology and Immunology
Course
Microbiology and Immunology 2500A/B
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of 15
Near Earth Objects
Ziyu Liu
250 585 137
March 28, 2013
1086G Origin and Geology of the Solar System
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1. Introduction
Near-Earth objects (NEOs) are objects in solar system, whose orbits have been brought
into proximity with the Earth. Near-Earth objects include thousands of near-Earth asteroids,
spacecraft, meteoroids and comets. Every year, approximately 108 kg of meteoritic material
falls on the Earth, from the size of dust particles to several kilometers asteroids. (Ceplecha,
1992) Near-Earth Asteroids originate from the Main belt or the Main Asteroid Belt, a region
in solar system found between the orbits of Jupiter and Mars. Thousands of asteroids that
have fallen on earth were collected and catalogued. Near-Earth comets come from the outer
region of our solar system that was probably derived beyond the orbit of Neptune, the Kuiper
belt. As a result, comets that crosses Earth’s orbit must have very high elliptical orbits in
order to reach the Earth due to their distance to our planet. It is very important to investigate
and pay attention to those extraterritorial objects since sometimes their impact on Earth can
have drastic effect upon colliding. Asteroids with diameter of less than 10 meters enter
Earth’s atmosphere with little energy, only approximated to be the equivalent of the Little
Boy (The atomic bomb dropped on Hiroshima). These NEOs usually explode in the upper
atmosphere and vaporized. (Clark and David, 1994) However, historical event such as the
Tunguska asteroid gave out energy equivalent to 10 megatons of TNT and is estimated to
occur every 2000-3000 years which can cause considerable damage if landed on Earth.
(Shoemaker, 1983) This report will address the classification of various NEOs and look into
details about the current NEOs as well as NEOs that have come into contact with Earth, and
discuss how they are monitored and assesses in modern scientific way.
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2. Identification and classification
Near-Earth Objects can be classified as comets and asteroids base on the size and
compositions. Near Earth Objects normally include only short period comets and Near Earth
Asteroids can be further classified and divided into three groups, Atiras, Amor, Apollo and
Atens based on their perihelion and aphelion distance as well as their semi major
axes.(NASA, 2013) There are 9,683 NEOs have been discovered since February 2013, 93
were near-Earth comets and 9590 are near-Earth Asteroids. In the near-Earth Asteroids, there
are 5,214 Apollo asteroids, 3,613 Amor asteroids, and 751 Aten asteroids. Also, there are
1,360 NEOs that falls in the category of Potentially Hazardous Asteroids (PHAs). (The
Spaceguard Central node website, 2013) PHAs are asteroids that have the potential to cause
significant regional damage when impacting on Earth due to its humongous size, having a
diameter of minimum 100 to 150 meters. Specific definitions of NEOs are categorized in
table 1. Near-Earth Comets have the orbital period P less than 200 years, with its perihelion
distance q less than 1.3 AU, in fact, all the NEOs have the perihelion distance less than 1.3
AU and greater than 0.983.(Morbidelli A, 1989) Atiras are the assteroids that orbit inside
Earth’s orbit, it’s aphelion distance (Q) is smaller than Earth’s perihelion (Q<0.983 AU), in
addition to that, the asteroid’s semi-major axis is also less than Earth’s perihelion. Atens have
the semi-major axis(a) of less than 1. Both Atens and Atiras are Apohele asteroids, as known
as Inner Earth Objects (IEOs), due to their aphelion is entirely within the Earth’s orbit
(Q<0.983 AU), some people consider Atiras to be part of the atens. Apollos have a larger
semi-major axes than Earth’s (a>1.0 AU). Amors are orbiting strictly outside of Earth’s orbit,
having a greater perihelion distance (q) than Earth and some of them cross the orbit of Mars.
(NEO groups, 2013) Since Atens and Apollos cross Earth’s orbit, they have a chance of

Document Summary

1086g origin and geology of the solar system: introduction. Near-earth objects (neos) are objects in solar system, whose orbits have been brought into proximity with the earth. Near-earth objects include thousands of near-earth asteroids, spacecraft, meteoroids and comets. Thousands of asteroids that have fallen on earth were collected and catalogued. Near-earth comets come from the outer region of our solar system that was probably derived beyond the orbit of neptune, the kuiper belt. As a result, comets that crosses earth"s orbit must have very high elliptical orbits in order to reach the earth due to their distance to our planet. It is very important to investigate and pay attention to those extraterritorial objects since sometimes their impact on earth can have drastic effect upon colliding. Asteroids with diameter of less than 10 meters enter. Earth"s atmosphere with little energy, only approximated to be the equivalent of the little.