Tuesday, September 02, 2008

Why I Went to the Mountains (Part 1)

The Kepler Mission
Image Credit: Jon Lomberg / NASA

I went to the mountains because I wished to observe deliberately, to front only the essential facts of astronomy, to see if I could not learn what the stars had to teach. (Okay, I'll stop channeling my inner Thoreau.) But what would drive a person to travel 400 miles to sit on a mountain top in the fog and rain and thunder, drinking copious quantities of coffee, and forgo most sleep for a week?

The answer is different every time. But my current observing run is a nice, straightforward project.

Our project originates with NASA's upcoming Kepler Mission. Kepler is a satellite that will be launched next spring; it's primary purpose is to look for Earth-sized planets around other stars.

There are many ways to find planets around other stars. To date, most of the planets that have been found are by the Doppler Effect. The gravity of a planet pulls on its parent star, causing it to wobble a little bit as the planet orbits around. This method is best at finding big planets, because the bigger a planet is, the stronger its gravity, and the more its parent star wobbles. It just isn't possible with current technology to detect the pull of an Earth-sized planet on a sun-sized star.

Another way to find planets is to look for the fading of a star when the planet passes between us and the star. This event, called a transit, requires pretty special geometry to see, so from Earth we can see transits in only about 1% of solar systems. Big planets, like Jupiter, will block 1% of the light from their parent stars. This is pretty easy to see -- people have even seen planet transits with telescopes in their backyards!

But seeing small planets, like the Earth, is a tall order. If we were to look for an Earth-like planet around another star, we'd have to be able to detect a one-ten thousandth drop in the light of a star, and that drop would only happen once a year, and would last only part of a day. And, to make it harder, we don't know which star to look at or when to look!

That's where the Kepler mission comes in. Kepler will stare at 100,000 stars for three and a half years, looking for tiny dips in light that occur at least twice (and preferably three times) at precise intervals -- the signature of an orbiting planet. It's a tall order, but Kepler should be up to the task.

Alas, I'm not looking for planets. (I should be, these days people seem just to want to hire astronomers who look for planets.) But there is other science, besides planets, that Kepler can do, because it will be watching stars for tiny changes in brightnesses for over three years! Any science that involves watching stars change brightnesses can benefit from Kepler. And that's where my work comes in.

Tomorrow, I'll explain how changes in the brightnesses of a certain type of star can tell us a lot about that star, and how that ties in with both Kepler and my nights at the telescope.

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