Tuesday, February 08, 2011
The Kepler Bonanza, Making Sense of Over a 1200 Extrasolar Worlds
As well as the unusual Kepler-11 solar system, the Kepler spacecraft has so far reported 1235 planetary candidates around 997 stars. See the paper here for more detail (warning, huge PDF file over 100 pages long)
To put this in perspective, in four months of staring a a patch of sky in Cygnus the size of your outstretched hand, Kepler has come up with 3 times as many extra-solar planets (maybe), as we had discovered from 1995 to June 2010.
Trying to understand this firehose of information will be a bit of an effort. First off, all these transit candidates have to be independently confirmed. This will be a massive piece of work, especially and ground based telescopes can only monitor the region of space Kepler scanned for about 6 months of the year, and multiple transits will have to be observed.
Distribution of planetary systems picked up by Kepler, I've used slightly different cutoffs that the Kepler folks (eg, I've used a 0.8-1.25 Earth radii as the criteria for 'Earth-like" but Kepler goes down to smaller radii). Click to embiggen.
Secondly, there is so much data. Trying to wrap our heads around the data will be bewildering, even for folks who are used to large data sets.
As a service to the amateur community, I've made Excel Spread sheets of tables 1 and 2 of Borucki et al, "Characteristics of planetary candidates observed by Kepler, II: Analysis
of the first four months of data", the Star Characteristics (table 1) and the Planet Candidates (Table 2) so you can play with the exoplanet data. Also, Kevin Schlaufman has made a plain text formatted electronic table that joins up Tables 1 and 2 (hat tip to Systemic) which is good for correlating planetary characteristics with stellar characteristics.
If you use this please a) remember to cite Borucki et al., (they did all the hard work after all) and b) remember that most candidates are unconfirmed, so don't get too excited. Most candidates will be real, but perhaps 5% are false positives, so be careful.
As an example of what can be done I've made a Celestia file of the unconfirmed Super-Earth KOI 701.03, which may be in the systems habitable zone (it is currently the most Earth-like world in a habitable zone). First download newextrasolar.stc here, (I've updated it with KOI 701 if you have downloaded a previous version) then copy it into the Celestia extras folder. Then you need the file the sets out the exoplanet Kepler701b.ssc, download it here and copy it into the extras folder.
Now, at -11 ºC the calculated black-body temperature of the planet is hotter than the black-body temperature of Venus (how hot Venus would be if it didn't have it's crushing carbon dioxide atmosphere, for comparison, without earth atmosphere our black body temperature would be -18 ºC) . How hot it is really depends on the nature of its atmosphere.
If I get enough time I'll make a script which will auto-magically extract data from the spreadsheets into Celestia format.
Other implications of the Kepler data are that if it's results are representative of the galaxy in general, then around 50% of Sun-like stars have planets, and they may be at least one million Earth-like planets in habitable zones in the Milky-Way alone.
While Kepler has only found planets around 0.6% of the stars it's looked at, it has been looking for only 4 months, and for example, it would be very unlikely to pick up a transit of a planet with an Earth-like orbital period or longer. As well, most stars will not be correctly oriented for Kepler to see a transit, which is why a 0.6% find rate implies that there are LOTS of planetary systems out there.
The Journal Nature has some free articles on the hunt for exoplanets here and here, the Bad Astronomers take is here, and Life at the SETI Institute here. Systemic has thoughtful posts here and here and a great video here, Centauri Dreams muses here.
Join the Planet Hunters and search the Kepler data for planetary candidates yourself!