The volunteers on our Planet Hunters TESS project have helped discover another planetary system! The new system, HD 152843, 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. This exciting discovery follows on from our validation of the long-period planet around an evolved (old) star, TOI-813, and from our recent paper outlining the discovery of 90 Planet Hunters TESS planet candidates, which gives us encouragement that there are a lot more exciting systems to be found with your help!

Figure: The data obtained by NASA’s Transiting Exoplanet Survey Satellite which shows two transiting planets. The plot shows the brightness of the star HD 152843 over a period of about a month. The dips appear where the planets passed in front of the star and blocked some of its light from getting to Earth.

Multi-planet systems, like this one, are particularly interesting as they allow us to study how planets form and evolve. This is because the two planets that we have in this system must have necessarily formed out of the same material at the same time, but evolved in different ways resulting in the different planet properties that we now observe.

Even though there are already hundreds of confirmed multi-planet systems, the number of multi-planet systems with stars that are bright enough such that we can study them using ground-based telescopes remains very small. However, the brightness of this new citizen science found system, HD 152843, makes it an ideal target for follow-up observations, allowing us to measure the planet masses and possibly even probe their atmospheric composition.

This discovery was made possibly with the help of tens of thousands of citizen scientists who helped to visually inspect data obtained by NASA’s Transiting Exoplanet Survey Satellite, in the search for distant worlds. We thank all of the citizen scientists taking part in the project who continue to help with the discovery of exciting new planet systems and in particular to Safaa Alhassan, Elisabeth M. L. Baeten, Stewart J. Bean, David M. Bundy, Vitaly Efremov, Richard Ferstenou, Brian L. Goodwin, Michelle Hof, Tony Hoffman, Alexander Hubert, Lily Lau, Sam Lee, David Maetschke, Klaus Peltsch, Cesar Rubio-Alfaro, Gary M. Wilson, the citizen scientists who directly helped with this discovery and who have become co-authors of the discovery paper.

The paper has been published by the Monthly Notices of the Royal Astronomical Society (MNRAS) journal and you can find a version of it on arXiv at: https://arxiv.org/pdf/2106.04603.pdf.