Transiting Extrasolar Planets

Extrasolar planets, or exoplanets, are planets that orbit stars other than our Sun. They are of great interest to the scientific community for many reasons, but are very hard to detect. Planets are extremely faint light sources, especially when compared to their nearby host stars, so many different methods have been created and refined in order to keep discovering new exoplanets. One of the most successful methods currently is transit photometry.
A transiting planet creates a dip in the star’s light curve.

Transit photometry is focused around finding planets that pass directly between their host star and us during their orbit. As the planet eclipses its star, the starlight is very slightly dimmed. If this dimming is observed periodically, it is possible that it is caused by a transiting exoplanet. The data from the star can be graphed into what is called a light curve, shown here to the left. If it is indeed caused by an exoplanet, the depth of the change in brightness can also be used to determine the size of the planet.


Vanderbilt University is actually part of a team called KELT (Kilodegree Extremely Little Telescope), a project conducting a sky survey for transiting exoplanets around bright stars. They are already responsible for the discovery of multiple exoplanets, and hopefully they will find many more!

4 thoughts on “Transiting Extrasolar Planets

  1. Nice explanation of the transit method – I’ve always (well, since I learned of them at least) thought the methods of studying exoplanets were pretty interesting. It’s crazy how we can learn a decent amount about a planet by just looking at it, like figuring out its mass by measuring the stellar wobble its star experiences, using coronagraphs to take images even though it’s near its much brighter star, and spectroscopy to find out more about its atmosphere.

    One of the main goals of the James Webb Space Telescope that’s going up in the near future is to search for and study exoplanets, which is pretty cool


    1. Absolutely! One of the main drawbacks of the transit method is the relatively high rate of false positive detections. This is actually closely related to the research I am currently working on. One of the most common forms of false positive is called an eclipsing binary. This is when the star we are observing is actually part of a binary system, and we measure a drop in brightness when its companion star passes in front of it. Even though the star is much larger than a planet, the light from the companion gets blended with the host star to make it appear much smaller, and sometimes planet-like. Follow-up observations and spectroscopy are usually necessary to determine if the event was indeed caused by a transiting planet or a binary star system. Great question!

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