HW3Ans - 1. What are the primary methods by which we have...

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1. What are the primary methods by which we have detected extra-solar planets? Why are Jovians much easier to find by these methods? 4 points An extra solar planet is a planet beyond the Solar System. The vast majority have been detected through various indirect methods rather than actual imaging. Most of them are massive giant planets likely to resemble Jupiter. Planets are extremely faint light sources compared to their parent stars. At visible wavelengths, they usually have less than a millionth of their parent star's brightness. In addition to the intrinsic difficulty of detecting such a faint light source, the parent star causes a glare that washes it out, unlike the Jovian Planets. For those reasons, current telescopes can only directly image extra solar planet under exceptional circumstances. Specifically, it may be possible when the planet is especially larger than the Jovians widely separated from its parent star, and hot so that it emits intense infrared radiation. Some of the primary methods of detecting an extra solar planet are: Astrometry : Astrometry consists of precisely measuring a star's position in the sky and observing the ways in which that position changes over time. If the star has a planet, then the gravitational influence of the planet will cause the star itself to move in a tiny circular or elliptical orbit about their common center of mass. Radial velocity or Doppler method : Variations in the speed with which the star moves towards or away from Earth — that is, variations in the radial velocity of the star with respect to Earth — can be deduced from the displacement in the parent star's spectral lines due to the Doppler effect . This has been by far the most productive technique used. Pulsar timing : A pulsar (the small, ultradense remnant of a star that has exploded as a supernova ) emits radio waves extremely regularly as it rotates. Slight anomalies in the timing of its observed radio pulses can be used to track changes in the pulsar 's motion caused by the presence of planets. Transit method : If a planet crosses (or transits ) in front of its parent star's disk, then the observed brightness of the star drops by a small amount. The amount by which the star dims depends on its size and on the size of the planet. Circumstellar disks : Disks of space dust surround many stars, and this dust can be detected because it absorbs ordinary starlight and re-emits it as infrared radiation. Features in dust disks may suggest the presence of planets. Eclipsing binary : In an eclipsing double star system , the planet can be detected by finding variability in minima as it goes back and forth. It is the most reliable method for detecting planets in binary star systems.
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This note was uploaded on 03/24/2008 for the course ASTR 100Lxg taught by Professor Dappen during the Fall '07 term at USC.

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HW3Ans - 1. What are the primary methods by which we have...

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