You may have seen our previous post announcing the discovery of four new planet candidates by the Planet Hunters NGTS. If you haven’t, check it out here. We wanted to share more details about what we know so far about each candidate and the efforts we’ve made to collect follow-up data to see if they are indeed exoplanets. After determining that these candidates were worth further investigation, the first step was to fit the data using more complex models. This is what is usually meant by phrases like “modeling estimates” and “fitted results” that you’ll see below and in other science communications. Each of these candidates poses its own challenges in confirming whether they are truly planets, but the fact that we already have four planet candidates is a positive sign for the future of the project and a true testament to the great work of all the Planet Hunters NGTS volunteers.
Subject 69695263: This is the most likely candidate so far as the transit is very clear and modeling estimates are promising. We believe this is a hot Jupiter orbiting a “K dwarf” star, which is a star that is slightly smaller and cooler than the Sun. We estimate the radius of this planet candidate to be 1.09 times the radius of Jupiter, which we will denote as R.p=1.09rJapThe planet orbits its star every 1.74 days, meaning that by the time you turn 18 Earth years, this candidate planet would be almost 3800 years old (assuming it exists and is habitable, which is not possible). We have received data on this candidate from the Zorro team (more on the Zorro instrument and subsequent efforts here), which indicates that, as far as we know, the host star is isolated from other stars, meaning we are a little more confident that this is not a false positive signal from an eclipsing binary. There is still a lot of work to be done before we get close to possibly confirming or verifying this as a planet, but we are cautiously optimistic about this candidate.
Subject 69593857:
This candidate is a bit of a head-scratcher, as we only observed one complete transit and a few partial transits (i.e. only the beginning or end of a transit). We estimate the orbital period of this potential orbiter to be 3.97 days, while radius estimates range from Jupiter-sized to almost as large as the Sun. This suggests it could be a planetary candidate, but it could also be an eclipsing low-mass binary (EBLM). These are interesting systems, but they are not the planets we are looking for. We have Zorro data for this candidate, but we do not see another star nearby. However, it is also possible that the signal is a false positive caused by “systematics”. Systematics is a general term that describes trends in the data that may not have been taken into account during processing.
Subject 69473954:
Like the candidate above, this one is tricky: the transit appears to be a graze (see this post for more on graze transits), so it’s hard to estimate the radius of the candidate accurately. The radius of the planet candidate is estimated to be at least R.p=1.50 ruJap This is already at the upper limit of what we consider to be a planet. The upper radius limit is estimated to be one solar radius, which means this could be a standard eclipsing binary. Unfortunately, for this candidate we don’t yet have the Zorro data to confirm this. This candidate and the previous candidates need to be studied further to really understand what it actually is.
Subject 69654531:
Finally, this candidate is very interesting because, if our initial estimates are correct, it would be one of only a small handful of giant planets ever discovered orbiting close to a small host star. The transit depth of about 12% is much deeper than typically expected for an exoplanet transit, yet the host star’s radius is only 1/3 of the Sun’s. We therefore believe this could be a hot Jupiter of radius R.p=1.13rJaporbits an M dwarf star with a period of 2.10 days. This type of system is very rare and a real surprise to find, since our current understanding of how planets form suggests that such a large planet could not have formed around such a small star, since there would not have been enough time for it to form, nor the material to do so. The Zorro data for this candidate is also encouraging, as no companion star has been seen. We hope to gather more data on this object in the coming months, if possible, so stay tuned!
These four new candidates are really exciting. They were not found during the initial check of the data by the NGTS team. This means that the Planet Hunters NGTS project has really proven that it has the potential to be a complementary search that helps the NGTS discover as many planets as possible. We couldn’t have done this without the collaboration of all the people who classified objects in the Planet Hunters NGTS. There are still many objects to classify, so we are looking forward to seeing what else you all will help us find in the coming days. We will be presenting these candidates at the British Exoplanet Conference in Edinburgh next week, and then we will check back later with the latest results from the project to look for more possible planet candidates. We also plan to publish the first results of the project in a paper and submit it to an academic journal.
