Besides planets, satellites and asteroids, the solar system contains comets (hair in Greek). The roaming comets originate in the depths of the space in several light years. The number of periodic comets is of the order of 2000. Comets, small spheres of ice travelling between stars, were surprised by the Sun. Their orbits have elliptic trajectories extremely eccentrics around the Sun. The most known periodic comet is the Halley's comet which approaches the Sun every 76 years.
When a comet approaches the Sun, the outside layer vaporizes and forms a gaseous envelope (coma). The solar radiation exercises a pressure on coma and force particles and gases to go away from the Sun by forming a brilliant tail of ionized particles.

Comets shine in the memory of the humanity. They made for a long time figure of misfortune, disasters and also herald of turnover, for a time when not satisfied with our real troubles, we accumulated it of imagination. It is not the messenger of the misfortune, it is the guard of past, the one who detains the keys of our origin. In 19th century with the separation of the sciences and the religion, the image of the comet is not negative any more. We can contemplate them during whole weeks, before they disappear to return, 10, 100 or 3000 years later. They are the tramps of the sky, the messengers of the space.

images NASA of the comet Wild 2, taken by the probe Stardust in 2004.

We can say that a comet is a big dirty snowball mixed in some dust, having in its center a big pebble. In 1986 a probe went to photograph the very close Halley's comet (600 km) returning extraordinary images of the nucleus the size of which is 16 km on 8 km.
Comets come from a place called the cometaire sphere, the vestige of past and distant reservoir which surrounds the solar system. This sphere cometaire a date of a period when the primitive solar system had not formed planets yet.

There is 5 billion years, a supernova explodes. The shock wave propagates in the space and on its road it meets a nebula. The cloud condenses to give birth to the Sun in the center and any goshawk a gaseous disk flattened in rotation fills with body which circulate everywhere. Some of these bodies agglutinate and form planets. Numerous asteroids in the system and everything in the suburb, the cloud of Oort, reservoir of the future comets remain. By the fate of the disturbances certain pebbles leave one

day the cloud of Oort and dive in the direction of the Sun, warmed their gas evaporates, a long hair spreads, they became comets. That is why comets detain the most former archives of the solar system. In 2003, the Rosetta probe will be launched by Ariane 5 to achieve 8 years later, the comet Virtanen. During 17 months instruments will map the surface of the nucleus in only 10 km in height. A module will get loose from the probe to arise on the comet and plunge the hand into a virgin matter of 4,5 billion years.

Whom we are...

category : asteroids and comets

In 1994 the astronomers observe live a comet (Shoemaker-Levy 9) colliding quite hard the planet Jupiter. This fantasy of the collision becomes a tangible reality for us, in spite of the smallness of the Earth.
These celestial bodies in the whimsical orbits can appear without any warning. In January, 1996, an amateur astronomer discovers a comet in the inner suburbs of the Earth to 15 million km only.

5 km in diameter, it been massive enough to destroy a big part of the life on our Earth. These eons of collision to reminds us the vulnerability of our existence.
Comets and asteroids brought the fundamental elements of the life on Earth and paradoxically could take back it in a single impact. If one of these collisions can have disastrous consequences for our planet, they probably contributed to

the appearance of the life on Earth, to the period when comets and bombarded asteroids the Earth in all directions.
The scientists even intended to go astray delicately towards Mars, 2 or 3 of these travelers of the space, to give it an atmosphere, a hydrosphere, an ocean, brief to sow it.

comet West. 

comet Hyakutaké

comet Halley

comet Hale Boop

Comet Linear

Comet Ikeya