An extrasolar planet, also called exoplanet, is a planet outside the solar system. The first extrasolar planet was discovered by Mayor and Queloz in 1995.
In fact, we can't detect exoplanets with a telescope so we have to use an indirect way to detect them.There are three different method:
- the first is the method of transit,
- the second is the radical velocity method
- and the third is astrometry.
In this article we are interested by the transit method.
The transit is an indirect method of detection. It consists in studying the brightness of a target star. If the observed light intensity decreases and increases periodically, it probably means that a planet periodically passes in front of its disc and partially conceals the star it is turning about. It's the phenomenon of transit.
Below is a film that shows an experiment that explains how to measure the changings in the quantity of light coming from a light source.
The first extrasolar planet was discovered in 1999. The number of extrasolar planet
discovered each year have greatly increased since 2014. Today,1257 planet have been
discovered with the transit method.
All of those planets have a different period :
- the smallest period is a period of 0,17 day,
- the bigger period is period of 3725 day.
This is the graph of the mean orbital period year after year relative to the period of Jupiter:
They have a different size too:
- the smallest planet discovered have a radius of 0.03 Rjupiter,
- the biggest planet have a radius of 2.04 Rjupiter.
The average radius of the discovered planet is 0.44 Rjupiter.
This is the graph of the mean radii two year by two year:
With the time, some new technologies have been discovered and they help in the exoplanet
quest. We can see on the graph that year after year, smaller and smaller planets planets have been
discovered.
Jonas,Gabriel ,Lucas and Cedric