http://truthufo.blogspot.com/: Different methods of detecting planets

Friday, 22 August 2008

Different methods of detecting planets

The photometric detection
If, during its revolution around its star, a planet comes between it and an observer, the light it receives will decrease. The brightness variation, however, is low: 1% for a planet like Jupiter, 1 / 100 000th for a terrestrial planet. Besides, it takes only a few hours and is reproduced at intervals of time equal to the period of revolution of the planet (one year for the Earth).

Disruptions dynamic
The stars and planets revolve around the centre of gravity of their system (Kepler's laws). The position of the star in the sky varies slightly over time: for example, the Earth produces a displacement apparent du Soleil less than one microsecond angle in one year. A fairly precise time monitoring the position of the star (astrometry) would chart its trajectory and boost the characteristics of the planet disruptive. The planet also induces a variation of the radial velocity of the star compared to a fixed observer. Thus, the Sun undergoes a change in radial velocity of a few cm / s in one year under the action of the Earth. The spectrographs capable of measuring the radial velocity with an accuracy of 10 m / s have been developed and used to search for giant planets. The planets that have been highlighted masses are equal to or greater than that of Jupiter and orbits located on very close to their star: less than 1 to 2 astronomical units (AU), while Jupiter orbits at about 5 AU from the Sun .

The effects of microlenses
The passage of a star (or a galaxy as in the diagram) near the line of sight of a distant star can lead to the observer a slight variation in the brightness of the distant star (the phenomenon of gravitational lensing ). If the star is more déflectrice accompanied by a planet, a second phenomenon lens, less intense and shorter, will occur. Following 35 million stars (8 years), are thought to be able to detect by this method a few hundred giant planets and a few dozen planets. These various indirect methods of detection will assess the rate of occurrence of extrasolar planetary systems, to determine the mass distribution of planets, their distance from the central star, and so on., Important parameters of training and l 'Evolution of planetary systems.

The direct imaging
The lack of power tools for direct observation current does not detect extrasolar planets. Indeed, between star and planet, the contrast of brightness is very high and low angular separation, even in the case of systems close to us. The coronary, which is artificially to overshadow a star to observe its immediate environment, can solve the problem of contrast. Interferometry can increase significantly the angular resolution. By combining the light after several distant telescopes observing the same region of sky, it leads to an angular resolution equal to that would be obtained with a gigantic instrument opening equal to the distance between the telescopes. Projects based on the use of black beaches (speckles) produced by atmospheric turbulence, or on interferometry are under consideration.