Exoplanet detection: Transit Method

Credit: ESA

How to find an Extrasolar planet

There are three main detection techniques that can be used to find extrasolar planets. All of them rely on detecting a planet's effect on its parent star, to infer the planet's existence.

The three techniques are simple in principle but difficult in practice because extreme precision is needed to register the planet's effect on the much larger star. This is also difficult from Earth because the atmosphere distorts our view of the stars, limiting the accuracy of the observations. Space missions can overcome this problem. The methods in question are:

• the radial velocity method
• the astrometry method
• the transit method

These methods are all referred to as 'indirect' methods.

from ESA website (click to read complete article)

When a planet crosses in front of its star as viewed by an observer, the event is called a transit. Transits by terrestrial planets produce a small change in a star's brightness of about 1/10,000 (100 parts per million, ppm), lasting for 2 to 16 hours. 

from NASA website

Exoplanet Detection: Transit Method (simulation)

The Exoplanet Detection: Transit Method model simulates the detection of exoplanets by using the transit method. In this method, the light curve from a star, and how it changes over time due to exoplanet transits, is observed and then analyzed. In this simulation the exoplanet orbits the star (sun-sized) in circular motion via Kepler's third law.  When the exoplanet passes in front of the star (transits), it blocks part of the starlight. This decrease in starlight is shown on the graph.  If the exoplanet is close enough to the central star, and has sufficient reflectivity, or albedo, it can reflect enough of the starlight to be seen on the light curve. In the simulation the star-exoplanet system is shown as seen from Earth (edge on view) but magnified greatly, and with the star and planet sizes not shown to the scale of the orbit. The radius of the central star (relative to the radius of Sun),semi-major axis of the exoplanet (in AU), radius of the exoplanet (relative to the radius of Jupiter), the exoplanet's albedo (reflectivity), and the inclination of the system relative to Earth can be changed.

from COMPADRE

• Other methods: http://en.wikipedia.org/wiki/Methods_of_detecting_exoplanets
• Exoplanet detection method (article): http://arxiv.org/abs/1210.2471