The solar system is composed of a star, the sun, which represents nearly 99.9% of the total mass of the system and of matter moving around it and which has a gravitational bond with it.
The solar system is composed of different zones that extend concentrically from its center which is occupied by a star: the sun!
A whole " world " revolves around our star, the Sun!
This incandescent lamp of 1,400,000 km in diameter!
This area includes the planets Mercury, Venus, Earth and Mars.
They are small rocky planets called telluric planets measuring between 4880km and 12.756km in diameter!
At 57.910.000 km distance, it is the planet closest to our star.
Mercury is also the smallest, its diameter is 4880, against 12.756km for the Earth.
This telluric planet is visible from the earth floor for only short periods.
Thus, astronomers can observe it above the horizon at dusk and dawn, during spring and autumn.
More rarely, the transit of mercury in front of the sun sometimes draws a small dark and moving spot on the solar disk.
His last appointment with the sun was for Monday, May 9, 2016!
Several mysteries surround this planet, such as its strange density.
It is estimated that 60% of the mass of Mercury would be composed of a metal core.
A surprising distribution: the planet is much denser than it should be in terms of its size!
Thus, the volume of the Earth represents 17 times the volume of Mercury.
The planet Mercury is therefore, like Venus, Mars and the Earth, a telluric planet.
In other words, a rock star.
Mercury would has a liquid core,composed of iron.
It measures 3.600km wide and would be covered with a coat.
Like that of the Earth, this mantle is composed of silicates, and is less dense than the nucleus.
It would be a relatively thin layer, which represents about 20% of the planet's radius.
Above, a crust, thick from 100 to 300km.
Finally, the small planet has a very fine atmosphere, composed of hydrogen, oxygen, helium, water, sodium and potassium.
A mercurial day has 59.65 terrestrial days and its year 87.97 terrestrial days.
During its long days, the temperature rises to nearly 430 degree celcius, temperature enough to melt the lead!
This heat escapes quickly, the atmosphere of the planet being too tenuous to allow it to be conserved!
The nights are then frosty, at almost -180degree C.
No other planet knows such variations!
By its size and its mass, Venus resembles the Earth, which is sometimes worth to be considered like 2 sisters!
Venus is the second planet closest to the Sun, and is very similar to the Earth in its size and mass.
Nevertheless, the rapprochement stops there.
It is indeed the hottest planet of the solar system.
Thanks to a powerful greenhouse effect, its surface is maintained at an average temperature of 470 degrees C.
It turns on itself slowly and in the opposite direction to that usually observed.
The rotation of Venus is so slow that two days correspond to about a year:
The diurnal cycle is 116.75 terrestrial days while it makes its revolution around the sun in 224.7 Earth days!
The nucleus of Venus, consisting of iron and nickel, would be formed of two parts: a solid central nucleus, probably surrounded by a liquid outer nucleus.
But the absence of internal magnetic field suggests rather that the nucleus would be entirely liquid.
Its mantle consists of silicate rocks and oxides, the size of which would reach half the radius of the planet.
Above is a thin silicate layer which constitutes the crust, the thickness of which would be about 20 km.
The plains cover 70 % of its surface.
Nevertheless, it bears the sign of a turbulent past:
long and deep canyons, mountains up to 10km altitude, volcanic dome, lava flows and craters of meteorite impacts.
Its thick atmosphere consists essentially of carbon dioxide, with an atmospheric pressure 92 times higher than that of the Earth.
This creates a powerful greenhouse effect explaining the high temperatures at its surface.
It turns very fast and in a retrograde manner, which results in winds of more than 360km/h in altitude above the equator.
In addition, between 32 and 90km above the surface, clouds composed of droplets and sulfuric acid crystals block 80% of the sunlight!
The Earth is the largest of the terrestrial planets.
It is covered with 71% by seas and oceans, hence its nickname of "blue planet".
It is also the only one known where water is present in its three forms: solid, liquid and gaseous, which allowed the development of life.
Its average surface temperature is 15degreeC, but the climate varies greatly depending on the location.
At 2900 km under our feet is hidden the core of the Earth, which includes a solidpart, called internal nucleus or seed
and a liquid part, mainly iron molten between 3500 and 5000 degree C, called external core.
Continuously animated around the solid core, this liquid mass works like a gigantic dynamo, which, like a rotating bicycle dynamo, generates electric currents and therefore a terrestrial magnetic field.
Above would be the mantle, the thickest layer of Earth, making about 2800km.
It is above all solid, with rocks like the peridotite.
It deforms slowly under the effect of heat from the core, causing convection currents.
These are large currents that allow the circulation of the heat produced in the heart of the Earth and its evacuation by the volcanic chimneys, also displacing the crust.
The crust has two components.
The oceanic crust, composed of dark volcanic rocks like basalt, is 7 to 8 km deep.
The continental crust is more varied and light, it measures from 25 to 70km.
The atmosphere is the superposition of several gaseous layers that surround the Earth and allow life on our planet:
The troposphère(0 to 10 km above sea level, where the ozone layer is located)
The stratosphere ( 10 to 50km above sea level),
the mesosphere ( 50 to 85km above sea level, Which has an icy temperature), the thermosphere ( 85 to 700 km of altitude, which is very hot),
and the exosphere (very fine thickness which forms a blue halo around the Earth when observedfrom Space).
It is composed mainly of nitrogen, oxygen and argon, as well as traces of other gasessuch as carbon dioxide.
The Earth has a natural satellite, which is 385,000km from it:
The moon has almost no atmosphere.
There is no liquid water and there is neither wind nor climate on its surface.
The moon turns on itself in 27 days and 8hours and puts the same time to go around the Earth.
Therefore, it always offers the same face to our planet!
The planet Mars is the 4th of the solar system by its distance to the sun.
It is a small rocky planet: 7 times less voluminous and 10 times less massive than the Earth.
It is one of the four terrestrial planets of the solar system.
It is colder than the Earth, in fact its average temperature is - 63 ° C.
It is called the " red planet " because its rocky and desert surface is covered with a dust rich in reddish iron oxide.
There are also many very high volcanoes and deep canyons.
The planet Mars has two small known natural satellites: Phobos (a size of about 22km and located 9400km from the planet Mars ), and Deimos (about 13km and 23500km from the planet Mars ).
The planet Mars has two moons!
The internal structure of the planet Mars remains largely unknown.
The small nucleus of the red planet would still be partially liquid and probably composed of iron and other lighter materials, such as iron sulfide.
Less densely packed than the core, the mantle is mainly composed of olivine and pyroxenes, minerals rich in iron and magnesium.
The crust forms an envelope, composed of volcanic rock.
Its surface, covered with red dust, bears traces of a turbulent past marked by volcanic activity, streams, erosion and meteorite impacts.
There are countless craters of impacts mainly in the southern hemisphere, younger volcanic plains in the northern hémisphère and a deep valley.
Valles Marineris, extends from west to east.
The Mars poles are permanently covered with very variable caps.
As on Earth, there are two but the south pole is higher so colder and more rich in seasonal carbon dioxide snow.
The north pole is warmer and therefore richer in water ice than the blue planet.
The atmosphere of Mars would be composed of 96% carbon dioxide, 2% argon , 1.9 % nitrogen ( N2 and N0 ), and the remainder corresponds to traces of oxygen , carbon monoxide, Water vapor and other gases.
The atmospheric pressure varies according to the complex condensation and sublimation cycle of the poles.
But it remains very low compared to that of the Earth with less than 1 %.
After our four telluric planets, an asteroid belt made up of millions of asteroids of different sizes and shapes, the largest of which is Vesta.
Moreover, in this belt, orbit a dwarf planet: Ceres.
This Zone forms a ring!
The asteroid belt lies between the orbits of the planet Mars and the planet Jupiter.
It is home to several hundred thousand objects ranging in size from dust grain to planetoid of a few hundred kilometers.
Vesta and Pallas, with a diameter of about 500km, are the biggest members of the group.
Ceres, with its 950km, is classified separately:
Since 2006 the International Astronomical Union has ranked it in the family of dwarf planets because of its spherical shape.
The asteroid belt is a relic of the primitive Solar System.
While the planets were formed by accretion, the region between Mars and Jupiter suffered the effects of orbital patterns produced by the giant planet, which limited the phenomena of accretion:
The acceleration of planetesimals produced numerous collisions.
These disturbances prevented the formation of a planet on this orbit.
The dust produced by collisions between spiral asteroids slowly towards the sun gives birth to the zodiacal light.
The asteroid belt has three major families:
Asteroids rich in carbon, those rich in silicates and those rich in metals.
As asteroids are small rock bodies similar to earth-like planets, their study gives man valuable information about the formation of planets.
These bodies have not undergone any external alteration apart from their mutual collisions, their characteristics as well as their physical properties allow us to better understand our own origins.
The classification of asteroids is rather complex, but one can distinguish in particular the "Neo"(geocroiseur).
Some of these millions of celestial bodies orbiting around the sun can sometimes lose their orbits and leave the belt due to solar and planetary disturbances and move on trajectories likely to cross the Earth's orbit.
We know 300 of them, we call them NEOs(Near Earth Asteroids), but rest assured, they are monitored very closely by automated programs (made me laugh ...)
These geocruiser are classified into three categories, depending on the number of times they cross the orbit of the Earth.
The Amors have a perihelion between 1.017and 1.3 Astronomical Unit.
There are about 250, discovered in the 70s near the Earth.
The first of this class was discovered in 1932 and named Amor.
The Apollos have a half-major axis of at least 1 Astronomical Unit, perihelion of at least 1.3 AU.
The Asteroid Apollo was also discovered in 1932.
It approaches us up to 3.7 million kilometers, which corresponds to about 10times the Earth / Moon distance.
This Asteroid cuts our trajectory twice during a revolution.
The Atens, with a half-major axis of at least 1UA, aphelion greater than 0.983UA.
Always close to Earth orbit, they can cross it up to four times a year, they are cataloged as being the most likely to hit us.
There are about twenty...
The Earth is constantly being hit by dustand small rock blocks, which we call shooting stars...
Alongside these near- Earth geocruiser, we distinguish the main belt:
Located between Mars and Jupiter (between 2UA and 4UA ), it is composed of asteroids divided into subgroups:
Hungarias, Floras, Phocaea, Corons, Eos, Themis, Cybeles and Hildas.
These groups are named according to their main asteroid.
There are finally three groups called Troyans, Thule and Hilda that resonate with Jupiter.
The Trojans are located not far from the Lagrange points of Jupiter ( 60 degrees in front and behind, in its orbit ).
There would also be some asteroids located at the Lagrange points of Venus, Mars and Earth called Trojans or Lagrangians.
Another category of asteroids, located in the outer solar system between Saturn and Uranus, is the Centaurs, like Chiron, for example.
Others like 5335 Damocles have orbitsvarying from Mars to further than Uranus, 5145 Pholus orbiting between Saturn and Neptune.
However, due to their distance, their composition is closer to the comets of the Kuiper belt than to the asteroids of the main belt...
Thus, Chiron is now classified as a comet!