From subject to candidate to planet: Processing all that data

You may be wondering how a subject goes from being one of thousands of subjects in the Planet Hunters NGTS project to becoming a candidate and then, hopefully, a bonafide planet! In this series of posts I hope to shed some light on the life cycle of a Planet Hunters NGTS subject.

Once a set of subjects are “retired” from the site, which occurs when all the subjects have received responses from at least 20 unique users, the data is collected from a huge “csv” file (that stands for comma-separated values). This contains every response by every volunteer for every subject included in the project and is effectively a giant spreadsheet, albeit one with millions of rows that would crash any standard spreadsheet viewer like Excel. This huge file is processed by a computer program and the most important data is pulled out and inputted into a large database that forms the hub of our operation.

From here, I can run another program that iteratively calculates scores for each subject for each possible response and computes weights for each user so that we can pay more attention to the classifications that identify transits more easily and therefore pick out subjects with high scores that might have been missed with simple vote counting. This is similar to the scoring and weighting schemes used in the Planet Hunters and Planet Hunters TESS projects, as well as many other citizen science projects. This lets me generate a list of the most promising candidates (e.g. subjects that are probably U-shaped) which are what you’ll see in the Secondary Eclipse & Odd/Even Transit Checks. I can then apply a similar program to classifications in these workflows to identify the subjects that are most likely to not have secondary eclipses or transit depth differences. These are the strongest candidates for being planetary transits instead of eclipsing binaries.

The next step is the most arduous as I look through all these candidates by eye (and there’s usually a lot of them!) and pick out the most promising ones to get a second opinion on. Filled with optimism and with candidates in hand, I show these to the NGTS team who evaluate them as a group to pick out the most promising planet candidates that we think are worthy of further investigation. At this point we would class these objects as potential planet candidates, although they can be ruled in or out through a series of tests using different data sources that I will go into in later blog posts.