The troposphere is the lowest layer of the atmosphere; it begins at the surface and extends to between 7 km (23,000 ft) at the poles and 17 km (60,000 ft) at the equator, with some variation due to weather factors. The stratosphere extends from the troposphere's 7 to 17 km (23,000 – 60,000 ft) range to about 50 km (160,000 ft). The stratosphere contains the ozone layer, the part of the Earth's atmosphere which contains relatively high concentrations of ozone. The mesosphere extends from about 50 km (160,000 ft) to the range of 80 to 85 km (265,000 – 285,000 ft).This is also where most meteors burn up when entering the atmosphere. The ionosphere is the uppermost part of the atmosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth. It is located in the Thermosphere. The Kármán line lies at an altitude of 100 km (62.1 miles) above the Earth's surface, and is commonly used to define the boundary between the Earth's atmosphere and outer space.[1] This definition is accepted by the Fédération Aéronautique Internationale (FAI), which is an international standard setting and record-keeping body for aeronautics and astronautics. Thermosphere: from 80 – 85 km (265,000 – 285,000 ft) to 640+ km (400+ mi). Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation by the small amount of residual oxygen still present. Exosphere: from 500 – 1000 km (300 – 600 mi) up to 10,000 km (6,000 mi), free-moving particles that may migrate into and out of the magnetosphere or the solar wind. Exosphere: from 500 – 1000 km (300 – 600 mi) up to 10,000 km (6,000 mi), free-moving particles that may migrate into and out of the magnetosphere or the solar wind. The ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone (O3). This layer absorbs 97-99% of the sun's high frequency ultraviolet light, which is potentially damaging to life on Earth. Ground level ozone (O3) formed from NOx, CO and VOCs. The majority of tropospheric ozone formation occurs when nitrogen oxides (NOx), carbon monoxide (CO) and volatile organic compounds (VOCs), such as xylene, react in the atmosphere in the presence of sunlight. Motor vehicle exhaust, industrial emissions, and chemical solvents are the major anthropogenic sources of these chemicals. Ozone is known to have the following health effects at concentrations common in urban air: irritation of the respiratory system, causing coughing, throat irritation, and/or an uncomfortable sensation in the chest. Reduced lung function, making it more difficult to breathe deeply and vigorously. Aggravation of asthma and increased susceptibility to respiratory infections.Tropospheric ozone is a greenhouse gas. The International Space Station (ISS) is a research facility currently being assembled in space. It has an altitude of 350-460 km above the surface of the Earth, and travels at an average speed of 27,700 km per hour, completing 15.77 orbits per day. The ISS is a joint project among the space agencies of the United States (NASA), Russia (RKA), Japan (JAXA), Canada (CSA) and several European countries (ESA). Space junk are the objects in orbit around Earth created by humans, that no longer serve any useful purpose. They consist of everything from entire spent rocket stages and defunct satellites to explosion fragments, paint flakes, dust, and slag from solid rocket motors. The U.S. Strategic Command maintains a catalogue currently containing about 13,000 objects, in part to prevent misinterpretation as hostile missiles. Observation data gathered by a number of ground based radar facilities and telescopes as well as by a space based telescope is used to maintain this catalogue. Nevertheless, the majority of debris objects remain unobserved. There are more than 600,000 objects larger than 1 cm in orbit (according to the ESA Meteoroid and Space Debris Terrestrial Environment Reference, the MASTER-2005 model).