I’ve mentioned before just how difficult it is to find extrasolar planets. I’ve also made little secret of the fact that I’m a huge fan of the SuperWASP experiment which adds lenses to professional standard CCD cameras, essentially getting rid of the telescope in order to monitor a huge area of sky for faint dips in the light coming from a star which might indicate the passage of a planet in front of it. The technique works well – one of the leading teams announced the discovery of the largest known planet this way yesterday. (Largest – not most massive. That had me confused for a bit).
I know have a new appreciation for quite how difficult this is. Scrolling through the list of new papers, I saw that Clarkson et al. had published the first tranche of superWASP data, and the numbers in the abstract made me stop dead. They had worked hard to obtain 141,895 lightcurves (each of them tracing the brightness of a single star over time). Buried within this set were 2688 – that’s less than 2% – which have transit-like features. They then looked at those few thousand light curves by eye, and end up with 44 (0.03% of the original sample) which were worth following up further.
What next? Job done? Nope! Another 24 are removed to leave only events which are statistically significant, leaving 20. The next task is to search through everything that’s known about those 20 stars, a process which ruled most of them out. Finally, after a huge amount of work, we’re left with 0.003% of the original sample – 4 stars which might, just might, have planets orbiting them. Wow!