Kepler Finds Two Planets Transiting the Same Star

By now, this news is a few days old, but there was something I wanted to check on before noting it. Here's the story:

NASA's Kepler spacecraft has discovered the first confirmed planetary system with more than one planet crossing in front of, or transiting, the same star.

The transit signatures of two distinct planets were seen in the data for the sun-like star designated Kepler-9. The planets were named Kepler-9b and 9c. The discovery incorporates seven months of observations of more than 156,000 stars as part of an ongoing search for Earth-sized planets outside our solar system. The findings will be published in this week's issue of the journal Science.

Kepler's ultra-precise camera measures tiny decreases in stars' brightness that occur when a planet transits them. The size of the planet can be derived from these temporary dips.

The distance of the planet from a star can be calculated by measuring the time between successive dips as the planet orbits the star. Small variations in the regularity of these dips can be used to determine the masses of planets and detect other non-transiting planets in the system.

This is only part of a much larger array of findings from the Kepler project. More details here.

What struck me as interesting about this is how fast the planets are orbiting, which, apparently, related to how close in to the star they are. I wonder what the typical planetary system looks like, in terms of the distribution of larger vs. smaller planet. This could have implications as we play the game of messing around with Drake equation like calculations (but for life in general).

Would it be possible to assert that a small ("Class M" if you will) planet close enough to a certain size star is more likely to have life, and that large gaseous Jovian planets swooping around in the inner regions of a solar system would reduce the likelihood of that? Or, are Jovian 'inner' planets likely to have numerous "Class M" satellites, like this one?

My understanding (I asked NASA) is that we basically don't know this at the present time but characterizing the overall pattern of 'solar systems' is an objective of the mission. So stay tuned.


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Would it be possible to assert that a small ("Class M" if you will) planet close enough to a certain size star is more likely to have life, and that large gaseous Jovian planets swooping around in the inner regions of a solar system would reduce the likelihood of that?

Yes, mostly. At least, life based on the kind of chemistry our life uses. We need liquid water, which puts restrictions on temperature - not too hot, not too cold - the "Goldilocks zone".

It's generally assumed that wild swings in temperature would be problematic for getting life started, too - so eccentric orbits are presumed to be less hospitable. And big Jovians close to the star can destabilize smaller planets, which would tend to kick them out of the "Goldilocks zone".

Of course, these assumptions may be too restrictive. There may be "life as we don't know it." But until we find some, we won't know about it. :)

My intuition tells me that our current methods for detecting exoplanets are biased in favor of close-in planets. Our main methods are by detecting the gravitational pull (proportional to 1/r^2 where r is the distance from the star to the planet's orbit) or by detecting a transit (geometry favors close-in planets as they are more likely and more frequently aligned). I know of only one system that has been detected by direct imaging, and that is the very nearby Fomalhaut system, where we can resolve the angular separation between the star and its planets in Neptune-like orbits. It's also obvious that all three methods favor big planets, which are brighter, more massive, and more likely to be observed transiting.

By Eric Lund (not verified) on 31 Aug 2010 #permalink

I've been trying to put together a presentation on exoplanets and the subject keeps moving faster than I can keep up. From what I read, the large, closely orbiting hot jupiters are thought to have migrated inward from Jupiter-to-Neptune orbits. This migration would disturb and probably destroy any earthlike planets. So, I'm very eager to see earth-size planets in earth-like orbits where there is also a hot jupiter, as that would turn over the understanding of how these large planets got where there are and thus increase the chance of finding earthlike planets.