Planets extrasolar

The radiation balance problem is not specific to our solar system and can be applied to all stellar planetary systems, although the number of planets outside our solar system - so-called extrasolar planets - is unknown. As noted earlier, the highest 

Direct detection of extrasolar planets requires a body with a luminosity some 109 times smaller than its parent star to be detected. The wavelength maximum 

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How could extrasolar planets be detected In recent years, astronomers have developed four different methods of finding non-emitting objects (planets) and even, to some extent, characterizing them. These are ... 

The transit method requires that the central star, the planet and the observer are connected by a line of sight. The dark planet passes across the light source and thus diminishes its light intensity to some extent. Observation is only possible when observer, star and planet are in a favourable position, i.e., the planet lies between the star and the observer. In spite of this requirement, the method permits the discovery of planets of about the size of the Earth information is also available on the size, mass and density of the planet as well as on its orbit. Because of its limits of applicability, this method is not often used. In the case of the star OGLE-TR-56, it was possible to detect an extrasolar planet, the orbit of which is very close to its sun only a twentieth of the distance of Mercury away from it. The temperature of the planet was determined to be around 1,900 K its diameter is about 1.3 times larger than that of Jupiter, its density about 500 kg/m3 (Brown, 2003 Konacki, 2003). 

The masses of the planets so far discovered vary between about 0.02 and 18 Jupiter masses. There are also very large variations in the values of the semi-major axis of the planetary orbits. If the first two methods for the discovery of extrasolar planets are compared (Doppler and transit methods), Doyle et al. (2000) point out the following facts around 40,000 photons are required to determine the transit of an extrasolar planet across the star HD 209548 using a photometer. But detection of the same system using variations in radial velocity requires 10 million photons. 

The number of known extrasolar planets grows monthly the first discovery was made on October 1, 1995, by Michael Mayor and Didier Queloz from the University of Geneva, who found a planet orbiting around the sun-like star 51 Pegasus. 

Using the Hubble telescope, the extrasolar planet HD 209458b (a gas planet with 0.7 times the mass of Jupiter) has been shown to have an extensive external atmosphere consisting of atomic hydrogen it is possible that the hydrogen is escaping from the planet (Vidal-Madjar et al., 2003). 

The detection of small extrasolar planets (of around the size of the Earth) will be done by registering the infrared light which they emit. Interference filters will blot out the light emitted by the star in question. Because of the huge distance from the Earth, effects due to its atmosphere and its IR radiation will not interfere. Darwin is intended not only to discover planets but to analyse their atmospheres for possible signs of life. 

ESA - Exo-Astro-Biology (2001) European Space Agency, Publications Division Extrasolar Planets Encyclopedia http //www.obspm.fr/planets... 

These detection techniques have found heavy planets with up to 400 Earth-mass but are unlikely to detect Earth-mass planets because the Doppler shift is too small. The first extrasolar planet to be discovered by the Doppler variation technique was 51-Pegasi, with the results shown in Figure 7.9. Precise radial... 

Current extrasolar planets are all much larger than the Earth. The total count at present (9 September 2005) is 168 found in 144 planetary systems, of which 18 contain multiple planets. The first to be discovered was 51-Pegasi in the constellation of Pegasus by the radial velocity method. It is about 0.45 Mjupiter and has an orbital period around the star of about 4.5 days. Of the 168 planets found so far only nine are present within a habitable zone around their star. The survey of the star catalogue for planets has only just started and we have found a large number of planets very quickly - solar systems, at least, are not special. 

Extrasolar planets Planets around stars other than our Sun. 

Scientists have recently gained their first glimpse of a planet outside our solar system. The first extrasolar planet was detected in 1996 by the wobble that it transmits to its mother star as it circulates in orbit. But in 1999 astronomers were able to detect the light reflected from such a planet. It was slightly blue. 

The detection of light from an extrasolar planet was reported by A. C. Cameron, K. Horne, A. Penny, and D. James, Probable Detection of Starlight Reflected from the Giant Planet Orbiting t Bootis , Nature, 402 (1999), 751. 

Masses (relative to Earth) versus thermal equivalent radii for extrasolar planets. Thermal equivalent radii are the mean orbital distances from their stars normalized to the Sun s luminosity, which corrects for different stellar properties. Planets in our solar system (open circles) are identified by their first letters. Modified from Lunine et al. (2009). 

Some astronomers believe that the growing population of extrasolar planets may be misleading. Nearly half of the so-called planets recently discovered orbiting around other stars may actually be brown dwarfs. The standard method for detecting extrasolar planets can only detect the minimum mass of an orbiting object. The actual mass may be much greater. [For more information, see Ron Cowen, Are most extrasolar planets hefty impostors Science News 158(18) 227 (October 28, 2000).]... 

Finally, the committee calls attention to the importance of using remote sensing to detect and characterize extrasolar planets that could support alternative carbon-based life. In addition to looking for evidence of water in... 

Planet-formation studies uniquely benefit from three disciplines astronomical observations of extrasolar planet-forming disks, analysis of material from the early Solar System, and laboratory astrophysics experiments. Pre-planetary solids, fine dust, and chondritic components are central elements linking these studies. 

Daniel Apai is an Assistant Astronomer at the Space Telescope Science Institute. His research focuses on the observational characterization of the origins and properties of extrasolar planets and planetary systems. 

Jupiter and Saturn, but comparable to some observed extrasolar planets. 

One mechanism to consider might be planetary migration (Lin et al., 1996 Murray et al., 1998). Observations of extrasolar planets provide strong evidence that planets migrate after their formation (Lin et al, 1996). Resonances are observed in extrasolar planetary systems possessing multiple Jupiter-like planets. These resonances can only be explained if the planets migrated after ffieir formation (Murray et al, 1998). Two kinds of models can be considered. 

Seager S. (2003) The search for Earth-hke extrasolar planets. Earth Planet. Sci. Lett. 208, 113—124. 

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