NASA’s Kepler mission has discovered over 1,200 possible planets outside our solar system. The tally includes 54 planets in the “habitable zone” of their star – the area where conditions for life as we know it are present. Of those 54 potential planets, five are about the size of Earth. Here is a very nicely done animation of all the planet candidates found mapped to our own solar system.

I say possible planets here because of the way Kepler detects potential planets. The space telescope measures very small decreases in the brightness of stars as the object passes in front of them (that is, in between the star and Kepler). The potential candidates for planets are all of these decreases in brightness, but they have to be checked using other methods to make sure there isn’t some other explanation for them. One method of verification is to wait for three transits of the planet in front of the star, but this could tak as much as three years, since it depends on the length of the planet’s year.

This is extremely exciting stuff (NPR called it “historic“) because Kepler was only looking at a small portion of the sky (see the “field of view” animation on the NPR page) and it can only see a small portion of the planets that might be in that little portion (since the planets have to be in an orbit that puts them between the star and the telescope). The following comment by MeFite eriko sums up the significance of this nicely:

What Kepler has done is told us, quite simpl[y], that planetary systems are not rare at all. It’s estimate[d] that Kepler is watching 145,000 main sequence stars, and in four months, has candidates around 997 of them. That’s .6% of the stars in view. If we assume that percentage, it means that there are 600 million to 2.4 billion planetary systems in our Galaxy.

Just amazing. And we can be certain that Kepler won’t see all of the planetary systems in its field of view — any system where the planets don’t eclipse the star from our point of view is completely undetectable by Kepler. If a copy of our system was placed in the field of view, with only the Earth in it’s normal orbit, there’s a .47% chance that the ecliptic would be in plane enough for us to observe the transit and detect the Earth. This chance varies some by the size of the planet and a great deal by the distance — close in planets will be much more likely to have visible transits. Assume that 5% of the systems with planets are correctly aligned so that we see transits.

That means, now, that those 600M to 2.4B systems represent 5% of the total, and we’re now looking at 12 billion to 48 billion planetary systems in our Galaxy — out of a total of 100 to 400 billion stars. Assume half the lower number, 6 billion planetary systems per galaxy. Current estimates of number of galaxies in the observable universe is on the order of 150 billion, so at 6 billion planetary systems per, that’ s 900 billion planetary systems in the universe.

And that’s a lower bound!

I can’t help but think about what news like this means to people who think we are alone in the universe, or specially created. Even without further proof, it is like maintaining the idea that you “know” you are going to win the lottery, and then win again several times in a row.

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