A word from Bill Borucki: Kepler P.I.
Dear Planet Hunters:
I’m writing to congratulate you on your wonderful discovery of some unique new planet candidates. I began designing and working on the idea of a space-based transit mission in the early 1980’s so that we could determine whether Earths were frequent or rare in our galaxy. The project encountered many obstacles, but the Kepler team overcame each of them and celebrated the Mission launch in March 2009! It is exciting to see the bounty of planets that Kepler has discovered and it is especially gratifying that all of you have been willing to contribute so many hours of your time to help us discover new planets. I understand that collectively, your contribution amounts to more than 50 years of “human processing time.” We now stand at the threshold of detecting planets in wider orbits; planets that might be habitable worlds or might have moons that are habitable. Transits around these more distant planets will be different than many of the transiting planets that you’ve discovered so far – these planets will have transits that are longer in duration than the transits of close-in planets, but they will be more difficult to find because they will occur less frequently. I hope that you will redouble your efforts to find these rare but important long period planets. Good hunting. The Kepler team really appreciates your help!
Bill Borucki, Science Principal Investigator for the Kepler Mission
Planet Hunters 
Some transits are still impossible to determine. For example, take this simulation: http://imageshack.us/photo/my-images/850/planethuntersimpossible.png/
How can we determine this is a transit as compared to the rest of the information in the graph? And if there are tools that can do this, why don’t we have them? I worry we’re just giving a distorted sense of exoplanet populations here.
(That’s http://talk.planethunters.org/objects/APH10915660 by the way.)
Hi Earl,
We added Kepler lightcurves into the Planet Hunters database with simulated transits, spanning the range of exoplanet radii and orbital periods, to test which kinds of transiting planets can be detected with Planet Hunters. If users flag 100% of the Jupiter-sized planets with orbital periods shorter than 30 days, but only 50% of the Neptune-size planets with orbital periods shorter than 30 days, then we know that the number of transiting Neptunes in the real light curves is a factor of two larger than what has been flagged. This provides a powerful statement about the fraction of transiting planets that could only be made with the Planet Hunters collective.
It might seem like we’re testing you or trying to train you to identify transits, but we’re really testing the project. The simulations are critical for determining the statistical completeness for planets as a function of size (depth of the transit event) and orbital period (number of transits). This is a really vital part of the project, with these simulated transits we can answer these really interesting and fundamental questions about how solar systems and planets form. Some of the simulated planets like large Jupiter-sized planets will be really easy to spot while others will be near impossible to identify especially for the extremely small planets, but don’t be discouraged if you didn’t find the simulated transit. That’s okay, that’s part of the experiment. We don’t know what Planet Hunters will be able to detect so we have to look at the look at range of possible planet radii and orbits.
Cheers,
~Meg