Exoplanets |
|
|||
| automatic translator | ||||
| Definition |
category : planets |
|||
| |
||||
| " Are we alone in the Universe? ". This question trots in the head of our astronomers for a very long time. To answer this question it is necessary to know if it exists or not the other planets on which could develop other forms of | life where from the collection in exoplanètes. Exoplanètes is situated by definition outside our solar system. Seen the large number of existing galaxies and the large number of stars which they contain, the search of these exoplanètes | or extra solar planets, is unlimited. To detect such planets is not however well-to-do: they are very remote from us, do not produce light and the star around which they turn, blind the observer. | ||
| Same Hubble cannot see Pluto |
category : planets | |||
| |
||||
| Even the spatial telescope Hubble The telescope Hubble is an American and European optical instrument allowing to observe the light in the visible, infrared and ultraviolet domains. it is placed in orbit around the Earth at a 580 km height so avoiding the disturbances due to the ground atmosphere. it includes a concave parabolic primary mirror which sends back the incidental light on a convex hyperbolic secondary mirror. These two mirrors are placed in a configuration said about Cassegrain. The light so harvested by cameras or spectrographs is then dismissed to be studied on Earth. can see Pluto only under the shape of a small task. How thus find an extra planet solar, millions of times more remote than Pluto if we cannot see it. The Earth turns around the Sun but really, if a star is accompanied with a single planet, both | turn around the centre of mass of the system which they compose. Considering the sharply bigger mass of the star, this center is closer to this last one than to the planet. Even if it is inside the star, it does not correspond exactly in the center of this one. The star thus shows a certain | variation provoked by the presence of the planet. This technique consists in discerning the variations in the specter of the light emitted by the star. By Doppler effect, this one seems more red if it goes away from the observer, more blue if it approaches it. | ||
| Presence of planets |
category : planets |
|||
| |
||||
| By measuring these variations, we can
calculate the movement described by the star and to deduct the presence
from it and the characteristics of the possible planets which accompany
it. In our solar system we observe a light oscillation of the Sun on a
cycle of 12 years, what corresponds to the cycle of gravitation of
Jupiter. Another technique consists in observing the cyclic variations
of brightness of certain stars. The passage of a planet between the Earth and the star leads a modification in the light which reaches us from this last one. We can also base themselves on this fact in the search for extra solar planets. These two observations are going to be able to bring to light the presence of planets around a star, it does not more remain than to look its indications. |
|
|||
 Spectrography
: Study of specters by means of a spectrograph, a device
intended for the photographic recording of a brilliant specter. The
spectrometry is the analysis of the specter of a radiation. The term
radiation is to be taken in the broad sense, because he can involve a
brilliant radiation, in a wider way an electromagnetic radiation, but
also a mechanical wave as the sound or the seismic waves, or still
particles. The movement of the dark lines in the
specter of the star is the signature of the movement of the planet and
the star around their centre of gravity. Credit: look-out observatory of
Paris / ASM Emmanuel Pécontal |
||||
| The hunting in exoplanets |
category : planets |
|||
| The hunting in exoplanètes thus consists in tracking down the oscillations of stars in the characteristics identical to the Sun. This hunting limits itself at the moment that to the gaseous giants witch turn around their star. More and more new stars are discovered with cyclic oscillations. Another characteristic of the presence of planets around a star is the variation of brightness of this star. When a planet walks past a star its brightness shows a small variation. This variation can reveal the size and the other characteristics of the planet. | Telescopes with measure of brightness, the
precision of which allows to detect until 1 % of variation, confirm the presence of planets
around a star because in every passage of the planet in front of the star a
darkening with place. A repeated cycle confirms a passage of object in
front of the star. More than 70 huge planets were so detected. |
|
||
| An unexpected discovery |
category : planets |
|||
| The scientists thus left in search of stars
the oscillation of which stretches on an around ten years, as our Sun. The star 51 Pegasus which is situated in 50 years light of us, oscillates with a cycle amazing at 4,2 days. There is thus an enormous planet which turns all around with a cycle of 4,2 days. The discovery of this planet is a real thunderclap for the scientists of the whole world. |
New stars are discovered one after the other
and with them of similar huge planets, it are all planets in short
periods orbital. On the star HD209458, situated not far from Pegasus, a darkening takes place every 3,5 days what confirms the presence of a gaseous giant. It has a beam, 1,6 times as big as Jupiter and a mass of 60 % of that of Jupiter. it is very |
situated near of its star. It is one Jupiter warm. Other planets in the eccentric orbit were since discovered and their system is very different of our. These observations show that enormous planets can turn around their star with very short cycles, what questions our vision of the formation of a solar system from a nebula of gas and matter. | ||
| Importance of the giants |
category : planets |
|||
| The quantity of dust and gas determines the size and the quantity of planets which are going to constitute from this disk. With a more important quantity of dust and gas: another giant builds up himself, in time the gravitational strength of the third planet perturbs the others. With a less important quantity of dust and gas, there is no gaseous giant, only smaller planets with stable circular orbit. Simulations by computer, formation of a solar system show a surprising characteristic. If we introduce the third giant into the solar system, the system becomes unstable | and eventually loses one of the huge planets.
Graver still it also perturbs the planets of ground type which
eventually absorb by the central sun. It shows that the mass of gases
and matter of the nebula has a vital importance for the suite of the
evolution. If there is less dust and gas, certain researchers think that
the life cannot abound there because it is Jupiter which protected our
planet. By being situated in the external part of our system, Jupiter decreased bombardment of the earth by the numerous objects coming from the |
reservoir of comets. The objects which change orbit and which goes to the center undergo the attraction of Jupiter. This attraction is so big as these objects are absorbed. Jupiter has guard's role for our ground world. These giants in borders of the systems thus behave as shields preventing the collisions with the planets of ground type. Instead of occurring all 60 000 000 of years, the collisions would occur every 60 000 years, only a microscopic life could then develop there. | ||
| Simulation of the third giant in a system | It follows itself a disturbance of orbits | The disturbance is more and more big | ||
| |
||||
| |
|
|
||
| ... until eject a giant | ||||
| |
||||
| An incredible chance... |
category : planets |
|||
| The simulation also shows that in one or two huge planets the system remains stable. The planets of ground type can be only in a small percentage of stars. | The presence of Jupiter allowed the Earth to become a planet where abound thousands of alive sorts. The importance of a huge planet is thus essential in a | solar system, by looking one the other Jupiter we can find another earth. The constitution of our solar system is the result of an incredible chance. | ||
| List of the known exoplanets. See the site The exoplanets which lists stars and known exoplanets to this day. | ||||
|
Related subjects |
category : planets |
|||
| |
||||
|
|
Astronomy - october 15th 2007 |
