Earth's twin is out there -- somewhere

What are the prospects for finding planets farther out?

There are three very exciting missions NASA is planning right now that would advance the search.

The first one is called Kepler. It's a space-borne telescope that will be able to measure the tiniest dimming (caused by a planet crossing in front of the host star), to one part in 100,000, allowing us to detect Earth-like planets.

The goal is to image a huge chunk of the sky around the constellation Cygnus, monitoring 150,000 stars continuously for four years . . . It's scheduled to launch in 2009.

What about the other missions?

The next one NASA is pushing is the Space Interferometry Mission, which is being designed and built at the Jet Propulsion Laboratory in Southern California. What SIM will do is find Earth-like planets in the habitable zone around the nearest stars. SIM is going to find the nearest Earth twin a few light-years away.

And the third mission?

The Terrestrial Planet Finder. I listed it third because it's further technologically down the line. We had hopes of launching in 2016, but I think that's not likely. . . . It would take the first pictures of Earth-like planets. Look at our own solar system. Which of the planets is blue? Earth. So if you found another star with a pale-blue dot tooling around that yellow star, that blue color and chemical analysis of the planet might give us a strong suggestion of life.

When do you think we'll see the first Earth-like planet?

I would say within three years we will have the first suggestion of rocky, lukewarm planets. We won't have the spectra. We won't know if there's oxygen. But we will know there's a rocky planet warmed up by its proximity to a campfire, if you will, where water could be liquid.

Say we find an Earth twin, what do we do then?

I know exactly what we do. UC Berkeley, in conjunction with the SETI [Search for Extraterrestrial Intelligence] Institute, is building a new radio telescope north of Mt. Lassen in Hat Creek designed to search for radio and television signals from an advanced technological civilization. It's called the Allen Telescope Array.

If the array picks up radio waves, then what do we do?

There is a written protocol for this. Step A is to communicate broadly and uniformly to the world what you think you have found, so that everybody can follow up and double and triple and quadruple check your work. . . .

I would recommend that Step Two be a . . . conference, where all of the nations are represented and we talk about it. The immediate question is what message, if any, to send back.

Remember, any such dialogue will not be lively repartee, because a star 50 light-years away means it takes 50 years to get back to them and 50 years to get back to you, so the jokes will not have quite the timing that they have when Seinfeld is on stage.

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john.johnson@latimes.com