Not long ago I sent out a ‘tweet’ on the Centauri Dreams Twitter feed talking about the number of planet detection candidates the Kepler mission was working with. Almost immediately I discovered that the story had become unavailable at the Nature News site, making me wonder whether the figures were right, but the story is back up (available here) and I can cite it once again. Thus:

Since its launch on 6 March 2009, Kepler, with its 0.95-metre telescope, has been staring at the same field of stars near the northern star of Vega, looking for tiny reductions in starlight caused by a planet passing in front of a star’s face. In January, the Kepler team announced the discovery of five new exoplanets. [Kepler principal investigator William] Borucki says that the team, as of last week, has found 328 more candidates — but that as many as 50% of these may be false positives, where objects such binary stars confuse the picture.

328 candidates, and much work ahead in weeding out the genuine planets from the false positives. But that’s what this kind of work is all about, a reminder that we’ll need to let Kepler run its three-year course before we really have the data nailed down and have identified (we assume) some terrestrial worlds around Sun-like stars, not to mention small planets around M-dwarfs that may prove to be in the habitable zone. No need to be in a hurry for results, in other words, and if you read the Nature News story, you’ll see that there’s no point in hoping for quick answers anyway.

That’s because, in addition to the inexorable rhythms of good research, the Kepler team’s new policy, as recommended by a NASA advisory panel, may be to hold back data on 400 ‘objects of interest’ until February of 2011, by which time some false positives will be eliminated. The issue is tricky: Researchers are usually allowed to keep data private until publication, which allows for the kind of rigor to be applied that will ensure the work’s accuracy. Caution in making media announcements that could lead to later retractions is completely understandable. The question is how long a delay is reasonable, given the multi-year period Kepler needs to confirm some detections. We should have a final decision soon on whether the strict policy will be put in place.

This comes up now because in June, Kepler is supposed to be releasing data, exposing the information to a wider audience that can work with the material to confirm planets. That original policy would have required the team to have turned over its first 43 days worth of data, but now we wait for a final decision on possible policy changes that is due in a week or so. According to Nature News, the Kepler team hoped to censor 500 objects until mission’s end in late 2013, so the subcommittee’s recommendation actually represents a compromise.

From the article:

Many astrophysics programmes allow researchers a proprietary period with the data. For instance, guest observers on the Hubble Space Telescope get exclusive use of their data for a year before public release. But the tradition for NASA Discovery missions — small, principal-investigator-led missions like Kepler — is to make calibrated data available immediately. That policy has already been changed once for Kepler, last year, when the team was given more than a year to pursue confirmations and work out the kinks in its data processing.

But Borucki says more time is needed because a mission launch delay meant that the team missed out on a season of the ground-based follow-up observations that are needed to verify candidate exoplanets. He also worries about releasing “half-baked” candidates that the media will jump on without an understanding of their uncertainty. “My worry is less of being scooped than it is of putting out inaccurate estimates of what exoplanets are really like out there,” he says.

The mission team’s views aren’t unanimously held by other astronomers, and the paper quotes dissenting remarks from Scott Gaudi (Ohio State), who believes that other teams could help the Kepler crew work to confirm candidate planets. ESA’s Malcolm Fridlund, project scientist for CoRoT, is working under a system where data are kept proprietary for one year, but he’s quick to note that the upcoming PLATO (Planetary Transits and Oscillations of Stars) mission will set a different agenda, one that will require the immediate dissemination of data. I’m with Fridlund in believing that with fast release, “You get a larger community and you get a bigger workforce for free. It’s clear that the more people you get involved, the more support you get.”