Earth sciences

Topics: Asteroid, Solar System, Meteoroid Pages: 12 (800 words) Published: April 28, 2014
1. Title:EARTH SCIENCES
 
2. Course Name: Origin and Geology of the Solar System
3. Course number: 1086G
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Introduction
Near-Earth Objects (NEOs) can be defined as heavenly bodies or solar system objects that have been pulled gently by the gravitational force of the Earth bringing them close to into orbits and the Earth’s neighborhood. These NEOs include Near-Earth comets, Near- Earth asteroids, meteoroids and a few solar-orbiting spacecraft huge enough to be trailed in space before hitting the Earth. The collision of the NEOs in the past has had a significant part in shaping the biological and geological history of the Earth. Near-Earth asteroids (NEA) have orbits that rest between 0.983 to 1.3 astronomical units from the sun (Shapiro, 1999). Due to this the Earth’s orbit cross with some NEA orbits posing a collision danger. By 2012 August there were 848 Near-Earth asteroids that were larger than 1km and 154 of those had were potential hazardous asteroids (PHAs).Comets are mostly composed of ice water with engrafted dust particles. They are formed on the outer system of the planet. The asteroids are mainly rocky and are formed in the warmer inner solar system between the orbits of Jupiter and Mars (Bally, Reipurth 2005). Scientific interest in asteroids and comets is due to their status because they have unchanged debris from the solar system formation dated back to up to 4.6 billion years ago. Asteroids and comets give hints to the chemical mixture from which the planets took shape 4.6 billion years ago. NEOs are of high interest also because they present interesting scientific opportunities for both astronomical and direct investigation. They are also potential sources of extraterrestrial materials for man development economically. This is due to the fact that they can be explored through lower mission velocity due to their small gravity and their combination of less velocity with regard to the Earth (Yeomans, 2013). This makes them an appealing target for exploration. By the year 2012 three NEAs have been visited by spacecraft. This report will identify and classify current Near-Earth objects and their potential impact on the Earth. Identification and classification of Near-Earth objects

NEOs can be classified as comets, asteroids and meteoroids depending on composition and size. Comets generate meteoroid streams that create meteor showers while asteroids are members of the asteroid family Near-Earth Comets (NECs) are further limited to include short-period comets only. In terms of orbital elements NEOs are comets and asteroids that have a perihelion distance of less than 103AU. Near-Earth Asteroids

The majorities of NEOs are asteroids known as Near Earth Asteroids (NEAs) and are divided into groups (Apollo, Amor and Aten) depending on their aphelion distance, perihelion distance and their semi-major axes (Botke, 2002). Atens are NEAs that have semi-major axes that are smaller than the Earth’s. Apollo is an earth crossing NEA with whose semi-major axes is larger than the Earth’s. The Amor consist of earth crossing NEAs with orbits outside the earth but inside the mars while the potential hazard asteroids are NEAs that have a minimum orbit intersection distance of 0.05 AU or below or those that have an absolute magnitude of 22.0 or brighter. Near Earth Meteoroids (NEMs)

Those objects of less than 50 meters are considered near earth meteoroids. They are many in number. Most of them are size of sand grains or small rocks though occasionally a boulder sized meteoroid can cross the Earth’s path. If this happens a fireball streak is seen across the sky even during the day. Meteoroids usually burn up in the sky and therefore pose little danger to human beings. All the NEAs smaller than 1in the measuring scale are categorized as ‘Near –Earth meteoroids’. They are usually listed as asteroids on many...
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