Friday, March 6, 2009

Say Hello to Kepler

On Friday the Kepler spacecraft (right) was successfully launched into an Earth-trailing orbit around the sun. Kepler has me and most of the stellar, solar, and planetary physicists in the world really excited because Kepler will allow us to study stellar systems rather than seeing stars as simply points of light. Kepler is essentially a 1-meter optical telescope that is going to sit and stare at the same patch of sky for the next 3+ years. In that time, Kepler will observe roughly 100,000 stars every 30 minutes looking for variations in brightness caused by planets passing between us and the star. These transits should detect Earth-sized planets in the habitable zones of their parent stars, which will allow the extra-solar planets community to get an idea of just how common Earth-like planets are in our galaxy.

In addition, a smaller number of stars (~100) will be observed every minute, which will the stellar physics community to measure resonant oscillations for low degree modes (spherical harmonic degree less than 4). With this data we will be able to use seismic techniques to determine the age, interior composition, rotation rate, and possibly the differential rotation of these stars to within a few percent (current age estimates, for example, have errors of about 50%). This means that we will be able to start to observe sun-like stars in some of the ways we observe the sun. For people who do models of sun-like stars, this is big news as we will finally get data on the interior structure of these stars.

For both of these tasks, the advantage to Kepler is the high cadence coverage for long periods of time. Ground-based telescopes can resolve individual stars far better than Kepler, however they have a duty cycle of at most 50%. Kepler will have a duty cycle of about 99%.

On the stellar side, there are already two smaller satellites doing something similar. The MOST and CoRot satellites (respectively Canadian and French) have already done asteroseiesmology on a number of stars. One of their best results has been precise measurements of the acoustic modes of Alpha Centauri A and B, which look to be a very good solar analogues, which have lead to precise values of their ages, compositions, and rotation rates.

As we understand other stars, we gain a better understanding of how our own star works. Our sun appears to be a pretty average star, but Kepler may be the key to finally proving that it is.

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