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Whose planet is it anyway?

Since we announced, via this blog and via a paper we submitted to the Astrophysical Journal and released on the arXiv, there’s been a lot of talk about our wonderful seven planet system. If you remember, amongst the other discoveries we claimed to add a seventh planet to the six already known in a system going by the name of KOI-351.

One of the responses was by a team of astronomers in Europe, who released a paper on the same system, which they nicely describe as ‘a compact analogue to the Solar System’. In that paper, they claim to discover four of the seven planets in the system, including the same one that the Planet Hunters had identified. To make things more complicated, in news from the Kepler science conference yesterday, the Kepler team announced that they’d assigned the system the name ‘Kepler-90’.

So what’s going on? Partly, the confusion is because of the way the scientific publishing process works. Back at the start of the summer, the official Kepler candidates list indicated that the star had three known transiting planets. (KOI, incidentally, stands for Kepler Object of Interest, a designation given to a star once the automatic routines and Kepler team have discovered something interesting going on, but before it’s certain there’s a planet there). Cabrera and colleagues – our friendly European rivals – took a look at the system and found evidence for four more planets, wrote up their paper and submitted it to the Astrophysical Journal.

We, of course, knew nothing of this and continued to work on our own list of candidates, many of which ended up in the paper we released last week. The Kepler team released a new list of interesting transits that included three of the new ones, leaving just the seventh planet to be announced. That paper was also submitted to the Astrophysical Journal a couple of weeks ago. We knew the Kepler conference was coming up, and that others were after the same quarry – planets! – as we were, so rather than wait until the paper was accepted by the journal we decided to release it early. The arXiv is a repository of pretty much all recent astronomical papers, and it’s up to the authors to decide when to share their work; there’s no review of papers before they appear on the site.

Cabrera et al. presumably didn’t know we were on the trail of the system until our paper appeared. In the meantime, they’d received a referee’s report on their paper, and sent in a new version of the paper on the day our paper appeared on the arXiv. Understandably, they then decided to release their paper on the same day.

So who deserves the credit for the discovery of the seventh planet? That’s not a simple question to answer – if the glory goes to whoever announces first, then it belongs to us. If you prefer to give the honour to those who submit to a journal first, then we were beaten by Cabrera. If it’s whoever publishes first – well, both of us are still waiting on referees and the race is still on. For my part, I’d like to think that we both teams can share credit for independent discovery, and we can be hopefully that with so many different teams scouring the data in different ways little will slip through our collective net. In the meantime, the Kepler team have become more convinced by the analysis they’ve been doing have have promoted the system from a mere object of interest to a bone fide Kepler planet-bearing system – hence the new designation Kepler-90!

We have lots more science in the pipeline, and we’re confident that all the work you put in on Planet Hunters is still capable of making unique and valuable discoveries. With the recent announcement of yet more planet candidates in the data, there’s plenty of planets to go round.


PS In the rush to get the paper out, we’ve fallen behind on the vital task of collecting the names of those Planet Hunters who contributed to the discovery. Rest assured that the final version of the paper – that included in the journal once it’s accepted – will have a complete list. Apologies for the delay, but we really want to get this right!


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