Kepler’s been in the news lately, revealing some of its latest discoveries. At the time I’m writing this, Kepler has logged 1235 potential planets and 1879 eclipsing binary stars. Of the 1235 planetary candidates, 15 have been confirmed to be real planets. That may seem like a very small number, but it takes time to confirm these candidates with ground/space based telescopes. The number is sure to rise.
As I was looking at the Kepler site, it struck me as to how small Kepler’s view is of the entire sky. It covers an area of about 105 square degrees. Now that’s a pretty large area when you consider that our full Moon spans about a half a degree, and has an area of about .2 square degrees. But, if you think about it from the point of view of the entire visible sky, which covers 41,253 square degrees (encompassing both the northern and southern hemispheres), Kepler is only sampling 0.25% of the sky! If Kepler’s sample of our galaxy is typical of the entire galaxy, then we could expect a minimum of about 500,000 planets in the galaxy with equivalent short period orbits.
Remember that these planets pass between their stars and Kepler, so any star systems in which the planets rotate in a plane almost perpendicular to Kepler’s view would not be recorded. So, this rough number is even a smaller percentage of the potential total number of planets out there. Oh, and don’t forget about the moons that may orbit these planets (and others yet discovered) and could have atmospheres and environments conducive for life to form.
Out of these potential candidates, 68 are known to be Earth-sized and 288 fit the category of “super-earth”-size - 2-5 times the size of the Earth. These are all rocky-type planets, verses the gas giants like Jupiter. Some of these are also in or near the habitable zones of the stars they orbit. This is a region where temperatures on the planets would allow water to exist in a liquid state, essential for most life as we know it on Earth.
Almost two years of Kepler’s 3.5 year mission has passed, and it has documented 1235 planetary candidates. This means that these potential planets have passed in front of their parent stars at least 4 times in this two year period to provide reliable data to confirm that it’s a planet. In the next one-and-a-half years, more planets will be documented as they pass in front of their stars causing the star’s light to dim and allowing Kepler to record another transit. The longer Kepler looks at a star, the more planets it will see, because they are further from the star and have longer orbital periods.
If Kepler were looking at our Sun, it would have already documented Mercury, because Mercury orbits the Sun every 88 days. (Actually it would have to be a much larger version of Mercury to be seen by Kepler.) Venus would also have been identified, with its orbital period of 224 days, three transits could have been recorded in two years. Earth could also be a likely candidate, but unconfirmed with two possible transits in the two year observation period. But, Kepler wouldn’t have anything more than possibly one transit for Mars and/or the other planets beyond it during this time period. With Jupiter’s orbital period of almost12 years, it would take 48 years for Kepler to gather enough data to confirm its existence.
The cosmos is teaming with planets, I have no doubt. I also think that the cosmos is teaming with life, in some shape or form. Our own experience with extremophiles here on Earth should be a good indication that life will find a way. How advanced that life is, is open to debate. Time will tell.
If you would like to participate in identifying potential planets from the data that Kepler has produced, take a look at the site: Planet Hunters. At the site you will go through some training and then will be able to identify transits that may indicate a planet passing in front of a star. A nice way to be able to participate in a profession astronomy project.
As always, comments and discussions are welcome.
Till next time,