Limitations of the Transit Methods

        Even though the transit method for detecting planets around other stars is one of the most popular techniques that are being used there are limitations and there are challenges that have to be overcome to make this method even better. As I mentioned in my last post the smallest planet that has been found to date is Kepler 10-b. It's radius is 1.24 times that of the Earth which is promising but by far most of the planets that have been found are of the sizes of the gas giants with most being Jupiter sized and some even Super Jupiter sized. It is amazing that we are able to detect these planets but when we want to look for life we want to find smaller terrestrial like planets. These planets will be hard to find because they are a lot smaller than the star that they orbit, they also do not give of their own light and the sun gives off a lot more light than the planets.  This limits the ability for the transit method but there are other limitations as well. The first limitation is our limited angle. This means that only a fraction of those systems viewed will be tilted so that the planets will pass in front. This means that they have to be aligned to be able to catch a transit. The probability that they will align with a planet orbiting a sun-sized star at the same distance we are from the Sun is a very small .47%. This means that there is a very low chance that we would be able to catch a planet that is around a G type star that is in its habitable zone. This is discouraging but there is still a chance. Another one of the limitations is the high rate of false detections. This means that to confirm a sighting one has to see three or four transits. There can also be other techniques that can be used to confirm or to help confirm if there is in fact a planet. Also the transit technique can determine the planet’s size this method does not reveal its mass or details of its orbit as well as we have not yet been able to determine the atmospheric composition. This means that we have to use other methods to determine these other properties. For example if a planet was confirmed from the transit one can determine the radius of the planet. Then by using the Doppler Wobble method we can determine the mass. From these we can determine the density and then make models of what the planet could be made of and the different layers. There are limitations of this method but it is still a widely used method.

Information obtianed from: http://questional.com/blog/181-planet-hunting-techniques-transit-dimming-the-lights/