Planet Hunters Coffee Chat: Accelerating people-powered exoplanet discovery

An artists impression of the exoplanets in the TRAPPIST-1 system. The edge of a large star can be seen to the left of the image, followed by 7 smaller rocky planets in a row

Last month, I presented the work I did with NASA’s Citizen Science Accelerator at the C*Sci conference. We had to prepare a blog post to accompany our posters, so I thought I’d share it with you here!


Planet Hunters Coffee Chat involves citizen scientists in more stages of exoplanet discovery through a combination of citizen scientist-focused data examination tools, tutorials, and outreach videos. 

We created 40 videos on a variety of topics, including how to analyse NASA TESS data with Python coding, determine exoplanet properties and assess false positives. 

As a result, there has been a dramatic increase in the amount of ‘additional target analysis’ being carried out by citizen scientists, and a fourfold monthly increase in the potential exoplanet candidates shared with the exoplanet community.

The ‘Citizen Science Accelerator’

Planet Hunters Coffee Chat was created by a small team of astronomers and science communicators. We received NASA funding for a pilot study – called the Citizen Science Accelerator – working with the people-powered project Planet Hunters TESS

The Planet Hunters TESS logo with is a teal blue circle on a dark blue background. There is a yellow cartoon pl

Planet Hunters TESS is based on the Zooniverse platform where volunteers help astronomers to identify planets outside our Solar System (known as ‘exoplanets’). More than 30,000 citizen scientists have contributed to the project, identifying 120 potential exoplanets that were missed by machine detection.

How does Planet Hunters work?

New data from NASA TESS – the Transiting Exoplanet Survey Satellite – is released to our citizen scientists (via Zooniverse) roughly once per month. The volunteers sift through graphs (called light curves) to search for dips, signifying a potential exoplanet. Users can highlight these dips and this classified data is later checked by professional astronomers.

TESS records how the brightness of stars varies over time. When a planet passes (or transits) in front of its host star, some light is blocked and we see a dip in its light curve. This method of detecting planets is called the Transit Method.

Crowdsourcing these classifications through Planet Hunters TESS is important as humans can outperform machines in identifying certain types of transits, for example, when a planet takes a long time to orbit its host star (known as a ‘long-period transit’). 

If one of these planets is confirmed by scientists with ground-based telescopes and other techniques, the citizen scientists who highlighted the data are credited with the discovery e.g. in this paper identifying two planets which features 16 citizen scientists.

What’s the problem?

Planet Hunters is awesome – but we thought our team could make a difference with two main issues.

Astronomers are overwhelmed with data

Citizen scientists are prolific and often finish classifying the monthly TESS data release in just a few days. They’ve generated a vast number of classifications, many of which contain interesting star systems and potential exoplanet transits.

But so much data has been classified that professional astronomers are only able to analyse a small subset of the interesting systems identified.

Citizen scientists are underused

Humans are great at recognising patterns and classifying data, but this isn’t using citizen scientists to their full potential – many want to do more.

With the right resources, we thought citizen scientists could carry out more analysis after identifying an interesting target (e.g. ruling out a ‘false positive’ signal caused by an asteroid or some system effects).

This would not only improve the quality of the data being passed to professional astronomers, but also involve Planet Hunters TESS users in more of the exoplanet science. We’re calling it ‘Citizen Science 2.0’.

What we did

We created Planet Hunters Coffee Chat, a weekly video series about the tools that astronomers use in their research.

Coffee Chat covers topics including the science behind exoplanet transits and explains the scientific results from the Planet Hunters TESS team. But some of our most popular videos are tutorials showing citizen scientists how to analyse NASA TESS data with Python coding (using a package called Lightkurve).

We provide all the code featured in our tutorials as Jupyter and Colab Notebooks which can be downloaded from our website so citizen scientists don’t need any prior coding knowledge to get involved.

We gave citizen scientists more contact with professional astronomers.

We hosted monthly ‘live office hours’ where citizen scientists could ask questions to NASA astronomers and special guests over Zoom. 

We also held online ‘vetting sessions’ for citizen scientists to propose exoplanet candidates and have their analysis checked by professionals.

Check out Coffee Chat for yourself!

So, did it work?

We gained a small but dedicated following of citizen scientists who assessed the potential transits they found and even estimated the properties of exoplanets.

The Planet Hunters TESS team reported a dramatic increase in the amount of ‘additional target analysis’ being carried out by citizen scientists and posted on the Planet Hunters TESS discussion forums.

There has been a fourfold monthly increase in the potential exoplanet candidates shared with the exoplanet community via the online TESS planet candidate database.

What citizen scientists thought

We surveyed our user base to find out if Planet Hunters Coffee Chat improved their citizen science experience.

  • Coffee Chat gave participants confidence in their understanding of the exoplanet discovery process –  after watching our videos, the percentage of respondents who rated their knowledge as ‘strong’ or ‘very strong’ increased by 4.7 times.
  • 94% of respondents felt more involved in the exoplanet discovery process.
  • 83% felt their contribution to citizen science was more valuable.
  • 61% of respondents used their new skills to rule out a false positive signal.
  • Half of the respondents proposed a good exoplanet candidate which was submitted to the exoplanet community through Nora.
Quotes from anonymous users:

“PHCC has taught me about coding with Python, it has also taught me about different false positives scenarios (and how to rule them out!), and also taught me how to use SIMBAD, ExoFOP, MAST and ExoMAST!”

“I have vastly improved my Python coding skills with great code examples to help identify false positives and characterise possible planets. I can now run my own diagnostics in Jupyter Lab and with practice I now make a good contribution to the PHT community and vetting sessions.”

“I only knew about the ‘look for a dip in a light curve to find planets’. I learned a lot about eclipsing binaries, what systemic effects could cause dips. And how objects (asteroids/satellites/TNOs) in our own Solar System can affect the light curve if they pass through the TESS camera FOV.”

What’s next?

We’re hoping to get more funding to bring Coffee Chat to a wider audience.

Astronomy is one of the least diverse of all the STEM fields and data shows that most of the citizen scientists who engage on the Planet Hunters TESS Talk forums are men. 

While approximately one-third of our YouTube audience identifies as female, the vast majority of citizen scientists attending our ‘live office hours’ and ‘vetting sessions’ are men. We’d like to involve more women in these subsequent steps of exoplanet discovery.

We’re also exploring the possibility of reaching younger audiences by collaborating with high school teachers, however, we’d need to adapt the length and complexity of our tutorials to be more lesson appropriate.

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