The Kepler space telescope has now found 68 exoplanet candidates that are Earth sized and 5 of them are in the habitable zone of their parent star. Another 49 planets exist in the habitable zone of their parent star, but are much larger than Earth. However, this doesn't rule out the possibility that moons around these larger planets could have liquid water and environments conducive to life as we know it. NASA press release here: http://www.nasa.gov/.../kepler/news/kepler_data_release.html
Anyway, what impact do you think this will have with respect to the "Privileged Planet" hypothesis and other arguments based on the Anthropic Principle? Kepler is only able to scan a tiny portion of the stars in our galaxy, so what does this tell us about the population of planets throughout the rest of our galaxy and the distribution of Earth like planets across the entire universe?
I still don't know where I stand on this. I feel like there are still too many variables remaining. Surely it confirms the notion that life-bearing planets similar to Earth could be common, but I'm uncomfortable taking it much further than that.
That's as far as I am taking it too. I don't know what the range of the Kepler telescope is, but I can't imagine that it's effective range extends much beyond our little neighborhood of the galaxy. On top of that, in order to measure transits of smaller planets with less eccentric orbits the solar system has to be "on edge" with the telescope (at least from my understanding). They can still detect Neptune sized planets with highly eccentric orbits due to the star wobbling without needing a transit.
I'm also interested in the size distribution of the planets they've found: about half of the planet candidates found so far seem to be Neptune-sized, with smaller numbers being larger or smaller than that. Does this represent an accurate assessment of size distributions? Or is it still skewed toward larger planets because of methodological constraints?
From the press release:
quote:"The fact that we’ve found so many planet candidates in such a tiny fraction of the sky suggests there are countless planets orbiting stars like our sun in our galaxy," said Borucki. "Kepler can find only a small fraction of the planets around the stars it looks at because the orbits aren’t aligned properly. If you account for those two factors, our results indicate there must be millions of planets orbiting the stars that surround our sun."
I think there are two sources of bias in the methodology. First, planets closer to the parent star have a much better chance of being detected as a transit. Second, larger planets are easier to detect.
So if the planet system under investigation is not lined up perfectly on edge with us we would only see the inner planets transiting the parent star while planets further out would never pass between us and the parent star. On top of that, small planets like Mercury may very well not be detected. However, very small planets have a much lower chance of holding on to their water so they are not as important with respect to finding planets with life.
Did you mean inclination rather than eccentricity here?
Yes, that's the word I was looking for.
For large planets with eccentric orbits we can measure the movement of the parent star to determine the size and orbit of the planet. For smaller planets with nearly circular orbits (like the Earth) this technique can not be used. Instead, you need to observe a transit in front of the parent star to determine the size and (I think) the orbit of the planet.