[asteroid]
Asteroid, sometimes called minor planet or planetoids, asteroid are include member in our solar system. Asteroid smaller than planet but bigger than meteoroid. Comet and asteroid almost has equal big and because that asteroid sometimes difficult to be differentiated when observation. But there are visual appearance difference because comet have tail while asteroids do not.
First idea about existence of asteroids begins from suspicion of the astronomers at XVIII century about difference of distance that is too far dissociating Mars planet orbit with Jupiter, at the end its generating speculation that among orbit of that planet surely there are a unknown planet. Effort to find the mysterious object finally got result when on 1 January 1801, an Italian astronomer, Giuseppe Piazzi ( 1746-1826) from Palermo Observatory successfully finds object that is initially mentioned as " fifth planet". That "New Planet" then called Ceres, takes name a god of ancient nation, Sisilia.
In March 1802, Johann Olbers, an Germany astronomer find a other " small planet" which called Pallas. Then successively is found Juno by CL. Harding ( 1804) and Vesta by Johann Olbers ( 1807).
[asteroid around Jupiter]
Then, astronomical community use minor planet or asteroid to term call a group of small fairish space object with irregular form in ecliptic. Then to naming for asteroid, applies name given by the inventor and started by its invention serial number, for example 1 Ceres, 433 Eros, 2340 Hathor, and so.
Until now, Ceres was noted as the biggest asteroid with diameter around 1000 km. Around 16 asteroids is known to has diameter above 240 km, while the rest has diameter less than that. Asteroid generally composes from rock and metal. Only a few which we knew about the forming process of asteroid. One of theory is mentioning that asteroids are part from a planet falling to pieces as result of explosion or collision with other object. However, observation farther indicates that asteroid very possibly have never become part of a planet, because practically if all the asteroid is united as a one object, hence the merger effected object will have a real small diameter, precisely do not reach 1400 km(approximately 3,0-3,6x1021 kg), or less than half measure of our moon(4%mass of moon).
Now, thousands of asteroid have been successfully recognized. Many of them are located between Mars planet orbits and Jupiter, this area known as " asteroid belt" but some having digressing orbit. One of the famous is Icarus,(the name taken away from Greek legend figure about flying winged man try fly close to The sun). At perihelion (point closest with the sun), this asteroid stays at closer distance with the sun than another objects then this asteroid can burned when close the sun. Then the asteroid recognized with name Hidalgo, the orbit approximant reach Saturn orbit.
[asteroid belt]
There are some asteroid which the orbit cut earth orbit, this can be a threat for earth and the dweller. A kind of this asteroid usually called with term " Near-Earth Asteroid" ( NEA). An asteroid classified as NEA if the orbit can reach distance 13 AU ( around 195 million km) or less than the sun. The astronomers classifies NEA into three groups:
Amour: Asteroid which the orbit getting through Mars orbit, but doesn't enter earth orbit ( example: 433 Eros).
Apollo: Asteroid which the orbit getting through earth orbit with longer orbit period out of one years ( example: 1620 Geographos)
Aten: Asteroid which the orbit getting through earth orbit with orbit period less than one years ( example: 2340 Hathor).
Most of NEA predicted exit from asteroid belt because collision with other asteroid or because gravitation influence of Jupiter. Some NEA also estimated composes from comet which has been died. The biggest NEA which known is 1036 Ganymede with approximant diameter 41 km. Now the astronomers who merged into " Near-Earth Asteroid Tracking" ( NEAT) project that focusing in Maui, Hawaii, still noted and observes NEA with diameter 1 km or more that having potency endangers earth. Some of asteroids that getting special notice is Toutatis, Castalia, Geographos and Vesta. observation to Toutatis, Geographos and Castalia use supporting facilities for observation of radar being based in earth when the asteroid pass quickly in a short distance from earth, while Vesta is observed with space telescope, Hubble.
A collision with asteroid that having diameter around 10 km estimated already happened at millions year ago. This mentioned as one of possibility that cause the extinct of Dinosaur. One event that relating to NEA happened in the 1989 when an asteroid is having diameter 0,4 km pass quickly with speed of 74000 km/h at distance 640000 km from earth. the nearest distance asteroid trajectory with earth noted happened on 9 December 1994 when a NEA pass quickly at distance only 103500 km from earth (for comparison, average of distance earth-moon is 384400 km). With refer to that event indicates that threat from outside earth in the form of king sized space object at any times can hit earth and generates a big disaster.
[asteroid impact]
Since 1991, some space explorer satellite has passed asteroid belt area and sends many data to earth. In October 1991, space explorer Galileo gets through asteroid 951 Gaspra to make this object as the first observed asteroid through high resolution picture taken away from an space explorer. In August 1993, Galileo returns to pass quickly asteroid belt and send pictures from asteroid 243 Ida. Observation to this asteroid indicates that Ida has nature satellite then named Dactyl. Either Gaspra and also Ida classified as asteroid type structured S composes by chert element that rich of metal.
[asteroid picture]
On 27 June 1997, space explorer NEAR ( Near-Earth Asteroid Rendezvous) meet in short distance with asteroid 253 Mathilde. In trajectory during the 25 minutes, NEAR sends more than 500 surface pictures of Mathilde. This is first short distance picture from asteroid type C which most composes carbon element. Then, NEAR continuing the mission towards asteroid 433. Eros then successfully reached in February 1999. During approximately two years, NEAR orbits Eros from average thread around 24 km from the surface and does various investigations to form, measure, magnetic field, composition, internal surface and structure of the asteroid. Mission NEAR end on 12 February 2001 when the satellite does "suicide" mission by banging up itself to surface of Eros to get picture from very close distance from surface of the asteroid. This thing registers Eros as the first asteroid landed satellite made by human.
Source :
Wikipedia.org
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