Planet Hunters TESS 



Planet Hunters TESS is a citizen science project designed to identify exoplanets - planets outside our solar system -

 from data obtained by NASA's Transiting Exoplanet Survey Satellite, or TESS. The transit method is used to search for exoplanets; a transit occurs when a planet passes in front of its star, causing it to block out a small amount of light and a slight dip in the light that we see from that star. 


What is an exoplanet?

To answer this question we start closer to home and look at our own eight-planet Solar System (there used to be nine bodies but Pluto is now considered a dwarf planet). These planets orbit around the Sun, which is a star just like the billions of stars that are visible when we look up at the night sky. So while our solar system planets orbit around the Sun, exoplanets orbit around other stars. 

Why is this work important? Why do we care about studying exoplanets?

Finding and studying exoplanets helps us understand the Galaxy we live in and how Earth formed, as well as what may happen to it in the future. Since the discovery of the first exoplanet in 1995, much has been learned about how how planet form and about what kind of planets exist. One of the major findings was that all stars have at least one planet orbiting around them (on average), making planets much more abundant than we initially thought. This means that when you look up at the night sky, most, if not all, of the stars that you see will have at least one planet orbiting around it. Even though we have already found lots of exoplanets (more than four thousand), there are still gaps in our understanding of how these systems form and evolve. In order to fill these gaps in our knowledge, we need to find and study more exoplanets: we need to find young exoplanets, old exoplanets, exoplanets with short orbital periods and exoplanets with long orbital periods. By finding and studying exoplanets with a wide range of different properties, we can hope to understand our galaxy a little bit better. With Planet Hunters Coffee Chat you can get involved in this exciting process! 


The transit method.

Using the transit method to find exoplanets reveals a lot of information about the planet itself - the size of the dip in light is related to the fraction of light that is being blocked out by a planet - for a given star, a larger planet means the dip is larger, and a smaller planet results in a smaller dip.















However, the size of the star also affects the size of the dip. If the star is larger, the dip will be smaller because the fraction of light that is blocked by the planet will be smaller. See the image below for an example:


Space-based satellites such as Gaia can tell us the size of stars that TESS looks at, meaning that when a transit event is found, its depth can be used to estimate the size of the planet. 

Visual vetting vs machines.

You might be wondering why astronomers use visual vetting (looking at data by eye) when there are computers that can do this. Computer algorithms are very good at finding certain types of transit events; however, they also tend to miss other types of transits. More specifically, most transit search algorithms require at least two transit events for the algorithm to identify it. This means that machines are biased toward finding short period planets (planets where the duration of a year is very short) and tend to miss the longer period planets. 

Click here to watch the first Planet Hunters Coffee Chat video to find out why. 


Our ability to recognise patterns means that we don't have the same bias as computers, therefore we can identify transiting planets that algorithms miss. Planet that the algorithms tend to miss include longer period planets (which may be more similar to our Solar System planets) and circumbinary planets (planets around two stars). Finding these systems is important for our overall understanding of our galaxy.


Take a look at the Planet Hunters TESS results page of the Planet Hunters Blog for our most recent finds.

Other planet citizen science projects.

There are several citizen science projects that focus on the discovery, analysis, and follow-up ofexoplanets - planets outside our Solar System. The Planet Hunters TESS Coffee Chat team works in collaboration with these projects, in particular, Planet Hunters Transiting Exoplanet Survey Satellite or TESS. Learn more about the projects below and how you can get involved! 



Click on the links to find out more!  

Backyard Worlds 

Exoplanet Watch

Exoplanet Explorers

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