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A good planet is hard to find

By Lucianne Walkowicz, Special to CNN
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Finding planets around other stars
  • Lucianne Walkowicz: Astronomy answers many of our questions about the universe
  • She says the Kepler mission has enabled scientists to learn more about planets
  • The search is on for planets that are in the "habitable zone" and could support life, she says
  • Walkowicz: We should be wary of budget cuts that prevent us from learning more

Editor's note: Lucianne Walkowicz is a Kepler postdoctoral fellow at the University of California at Berkeley's astronomy department. She spoke last month at the TED global conference in Edinburgh, UK. TED is a nonprofit dedicated to "Ideas worth spreading," which it makes available through its website.

(CNN) -- It was much too late on a Tuesday when a fellow astronomer friend and I found ourselves catching a cab back to Berkeley, having missed the last train home. My friend promptly dozed off in the taxi, leaving me to chat with our driver -- who wondered how we could be out so late with jobs to go to in the morning.

I explained that we were astronomers, and naturally tended to be night owls (although I added that my now-snoring friend was a theorist and therefore accustomed to a more regular schedule). "Astronomers!" Our driver immediately began to pepper me with questions about the universe, and so I launched into telling him about my work. Think of it as "Astronomy 101: Wee Hours of the Morning Edition."

Watch an interview with Lucianne Walkowicz

One of the wonderful things about astronomy is that it's a very accessible science -- in principle the sky is available to everyone. Although one's access to the sky may vary due to light pollution or outdoor space, most people have wondered what lies in that great beyond -- and nowhere is that more true than in the search for planets outside our own solar system. Hard to believe, but it's only been a little over 20 years since the first planets were found orbiting other stars, and though astronomers have found several hundred planets during that time, it's been painstaking, hard-scrabble work.

In the past two years, however, the hunt for extrasolar planets has gone high-octane with NASA's Kepler mission. Kepler is a space-based telescope that fixes one field of our sky in an unhalting stare, seeking the tiny dimming of stars as planets orbit around them and block some of their light.

How to find planets

Kepler's primary goal is to figure out how common it is for planets the size of Earth to exist around stars like our sun. In particular, we're seeking Earth-sized planets in what we call the "habitable zone" -- the range of distance away from its star that a planet must be to have just the right temperature for liquid water to exist there. Not too hot, not too cold.

Kepler searches for planets by making very precise measurements of the light from stars. We can tell the size of the planet by how much it causes its parent star to dim. Big planets block more light and make the star dim more than little planets do.

That's part of why it's so important that Kepler's measurements of the starlight are very precise: If you want to find little planets like Earth, you need to detect very small changes! We also look for how often those dimmings happen, which tells us how long it takes for the planet to orbit its star -- in other words, how long that planet's year is.

Johannes Kepler, the 17th-century astronomer for whom the mission is named, determined that the time it takes for a planet to orbit is related to how far it is away from its star, so we use the length of the planet's year to figure out that distance and whether it's in the habitable zone. Bada bing, bada boom -- the search for another Earth should be easy now, right? Not so fast!

Kepler's first harvest yielded over 1200 new planet candidates, including the first-ever confirmed rocky planet -- a blindingly hot little world called Kepler-10b -- and many more new discoveries are on the way. Kepler's careful measurements have also revealed new mysteries about planets previously found. Just last week, astronomers announced that the planet Tres-2 is a pitch-black world, darker even than coal. Dmitri Sasselov on finding Earth-like planets

However, it's a big leap from detecting planets to figuring out which ones might support life. Just being a living creature here on Earth is pretty complicated. Humans obviously walk the surface of the Earth, prefer mild temperatures, and require oxygen to breathe and water to drink, but we also find microorganisms living in harsh environments -- radioactive, acidic, hot -- where we would never survive.

In my work, I try to understand what it's like to be an alien world orbiting another star by studying the stars themselves. Here on Earth, we experience the effects of our sun not only as warm sunshine on a summer day, but through solar storms that cause both the beautiful aurorae and the disruption of our communications satellites. Other stars have this kind of "space weather" as well, and Kepler's precise measurements of starlight are perfect for seeing these changes.

In essence, I'm asking: "Is our sun unusual? How is it different from or similar to other stars, and what does that mean for where we're likely to find life in the universe?" By studying the stars and how they influence a planet's likelihood of supporting life, we place our Earth and sun in context. That context helps us learn which are the stranger creatures -- human beings, or the exotic forms of life that like those harsh places on our own Earth.

The reason we focus our attention on finding Earth-size planets is that Earth is the only example of an inhabited planet we have, and so finding other planets as small as Earth is one step in the direction of finding planets that are Earth-like. It's still beyond the capabilities of our existing instruments, even our best planet-finders like Kepler, to determine whether a planet we find is really like our Earth. The surprising math of cities

To study the new crop of planets in detail, we'll need to use even more advanced space missions, ones that are capable of finding out whether we're looking at worlds with blue seas like our own, or dead expanses of long-solidified lava. Consider that at the beginning of the 20th century, many astronomers thought there might be canals on Mars, because our telescopes were not yet capable of seeing how truly alien the red planet is.

Unfortunately, even as we gain new insight into our place among the stars, the funding climate for U.S. astronomy threatens to blind us completely. In the same week that the European Union moved to increase scientific funding across the board, Congress suggested canceling the successor mission to the Hubble, the James Webb Space Telescope.

Many of the existing space telescopes, Hubble included, are nearing the end of their lifetimes, and one by one they will turn off. Without the James Webb Space Telescope, our eyes on the universe would be closed for the foreseeable future.

Even Kepler, a wildly successful mission that's already up and running, faces near financial starvation. Those dwindling resources have both scientific and human repercussions. Decreased funding means the loss of jobs, and fewer people working to find those planetary gems in the Kepler data.

Don't get me wrong -- it's an incredibly exciting time not just to be an astronomer, but to be a human being, winging through space on this watery rock we call home and wondering what lies beyond. But at a time when funding for science is in dire straits, it bears remembering that even as we ride the crest of newly discovered planets, we will never answer our most fundamental question -- Are we alone? -- if we don't continue to strive for technological advancement and commit resources toward unlocking the mysteries of the universe.

The opinions expressed in this commentary are solely those of Lucianne Walkowicz.