Artist's impression of what the two-planet system might look like
Artist's impression of what the two-planet system might look like
Credit: Nora Eisner

Citizen scientists identify nearby two-planet system

Astronomy and astrophysics
Exoplanets and planetary physics

With just a few clicks of the mouse, citizen scientists from around the world identified a small dip among thousands of points: they have just discovered a new planet candidate. Planet Hunters TESS, a citizen science project led by a team at the University of Oxford and hosted by the Zooniverse platform, uses the overwhelming power of tens of thousands of citizen scientists to discover planets outside of our own Solar System, known as exoplanets. The most recent and exciting new discovery is a two-planet system around a nearby star.

Amazing human ability

Citizen science projects, such as Planet Hunters TESS, highlight that in a time where we rely more and more on computers and algorithms to do everything, humans are still finding ways to out-perform machines. Modern day exoplanet researchers overwhelmingly rely on computer algorithms to spot tiny dips in a star’s brightness caused by planets crossing in front of the host star and blocking out some of the light. This method, known as the transit method, has been spectacularly successful, having led to the detection of thousands of exoplanets over the past 25 years. However, using a machine has its weaknesses: computer algorithms that search for planets tend to need at least two dips to recognise a pattern that may be due to a planet transit. If there is only a single dip in the available data, the planet often goes undetected by the algorithm. Humans, on the other hand, have an amazing ability to recognise patterns, and are able to detect these single dips in the brightness of stars that the algorithms often struggle to find.

However, the rate at which any one of us can visually look through data is far slower than that of computers. To overcome this limitation, the citizen science project Planet Hunters TESS is speeding-up the visual inspection of data by crowd sourcing the identification of exoplanets to tens of thousands of citizen scientists from around the world. Research using the Planet Hunters TESS project has shown that humans are almost as good at finding planets that have multiple transit events, but they excel at finding planets that exhibit just a single dip in the data. It is exactly this that led citizen scientists to be able to identify an exciting new multi-planet system that was initially missed by the computers.  

Great scientific value

This new exoplanetary system consists of two planets, that are similar in size to Neptune and Saturn in our own solar system, orbiting around a bright star that is similar to our own Sun: HD 152843. Multi-planet systems, like this one, hold a lot of scientific value, as they allow us to study how planets form and evolve. This is because the two planets must have necessarily formed at the same time, and out of the same material, but evolved in different ways over time resulting in the different planet properties that we observe today.

Even though there are now hundreds of confirmed multi-planet systems, the number of multi-planet systems with stars that are close enough such that we can observe and study them using ground-based telescopes remains exceedingly small. The proximity and brightness of HD 152843, however, is one of the properties that makes this new system stand out. The science team, led by PhD student Nora Eisner at the University of Oxford, was able to further investigate the properties of the two planets using telescopes in La Palma, Canary Islands, and Lowell Observatory, USA: ‘The ground-based follow-up observations, which are ongoing, have already revealed that both planets have very low densities and are thus likely to have very large gaseous atmospheres. Combined with the brightness of the star, these properties offer exciting prospects for probing the atmospheres and chemical composition of both planets in the future.’

A global endeavour

The dips in brightness caused by the two newly confirmed planets, were identified by 15 citizen scientists from around the world, including from Belgium, England, Germany, Iraq, The Netherlands, Russia, Singapore and the USA, who are now all co-authors of the published discovery paper. Along with 30,000 other Planet Hunters TESS volunteers, these citizen scientists regularly help to visually sift through data collected by NASA’s transiting Exoplanet Survey Satellite (TESS) in the search for new planets outside of our own Solar System. The motivation for taking part in the project ranges from scientific curiosity, a love for astronomy and space, to finding something to pass the time during a global pandemic.

‘I am currently working as a machinist, as well as a single dad to my young son who I wish to share my love of all things space with.’
Cesar Rubio, citizen scientist, California

The citizen scientists, who were informed of their involvement with the planet-discovery a couple of months ago, responded with excitement to the news. ‘When I analysed thousands of pictures of the light curves of stars obtained by the TESS telescope, I certainly hoped that it would be possible to discover a new exoplanet, but personally it seemed to me something distant, unlikely. And when I found out about the discovery a few months later, I was really very, very happy about it. It's hard for me to put it into words, but it's just amazing!’ said Vitaly Efremov, from Russia.

In this increasingly automated world, Planet Hunters TESS offers the opportunity for anyone to partake in scientific discoveries, contribute to cutting-edge published research and to prolong the moment where the machines outperform us.

Other citizen scientists who are named authors on the paper:

'I've helped with Zooniverse projects on and off for years, but since the lockdowns started last year I've found myself with a lot of free time. And while I can't do much stuck at home, helping out at Zooniverse makes me feel a little bit more useful.'
Michelle Hof, The Netherlands

'I got involved with Planet Hunters, right from the start. I try out every new Zooniverse project and obviously some interest me more than other. And what's not to like about discovering exo-planets. Just the idea that anyone can be part in discovering planets around other stars is simply mind-boggling. I find it actually quite relaxing to be classifying light curves.' 
Elisabeth Baeten, Belgium

'It is sometimes hard in our modern world for people with broad interests, because you need to specialize on something, so I embrace every chance to see beyond the end of my nose. And if by that I can discover something great, that's even better!'
Alexander Hubert, Germany

'(I think) I’ve been part of the project for years – since the beginning – I have been an amateur astronomer most of my life (over 50 years as an amateur)  – and I teach astronomy at the local university, as well as computer science and physics.'
Klaus Peltsch, Sault Ste Marie, Ontario, Canada