What are the methods for detecting and measuring extrasolar planets?

Answer 1

Radial velocity - Just like the star pulls on the planet, so does the planet pulls on the star - but only a bit. By observing a star for a long period one can detect periodical movements caused by an orbiting planet.

Transits - Sometimes a planet will pass in front of a star and hide a small portion of its light. By tracking a star's brightness, it is possible to detect a passage of a planet.

Micro-lensing - General relativity has taught us that massive objects bend light. If one star with a planet passes in front of another star we can see a distortion of light which can tell us whether a planet is present or not.

Direct observation - The most unlikely method, since extrasolar planets are hidden in their stars glare, but people are working on it.

Answer 2

The most common method use to detect planets involve measuring the change in light intensity of a star. By observing and measuring the light output of a star over a period of time, regular, periodic fluctuations in the intensity of the light output can indicate a planet orbiting the star. As the planet pass in front of the start, the measurable light is less.

Answer 3

The easiest is to search for the drops in the measured brightness of their stars when some of the planets transit across them. Not all planets do this however. This will tell you the planet's radius and its orbital period. This is called "the transit method" or "transit photometry"

Another popular way is to detect the "wobble" of the star as the planet gravitationally tugs on it while orbiting around it. Measuring this will give you the minimum mass of the planet and its orbital period. This wobbling is very hard to detect, so it must be done indirectly, by watching the light from the star shifted by the Doppler effect. This is called "Doppler spectroscopy" or "radial velocity method."

If you can detect a planet using both of these methods, then the mass of the planet is no longer a minimum mass, but you can determine the real mass, which you can combine with the radius to get a density which will tell you something about what kind of planet it is (a gas giant, or a solid terrestrial planet?).

Another way is to directly observe the star wobbling around. This is hard to do but is feasible for some of the closer stars. This is called "astrometry."

A more exotic way to do so is by waiting for a planetary system to pass in front of a background star. The foreground star's gravity will act as a magnifying glass, amplifying the brightness of the background star. The presence of a planet around the foreground star can, for some cases, cause further magnification or distortion to the light of the background star. This is called "gravitational microlensing."

Answer 4

There are four ways in which an exoplanet can be detected. Transit method- a planet passes in front of the star making it detectable Astrometry- the center of mass near a star is shifted by a planet making the star wobble Doppler shift- the wave length of the radiation coming from the star will shift if there is a planet present Radial lensing- when looking at pictures of the distant star there will be a streak of light present, this was predicted by Albert Einstein and his theory of relativity

Answer 5

gravitation tugs; astrometric technique; doppler technique