For the last 20 years, UC Berkeley astronomer Geoff Marcy has been the world’s leading planet finder. Of the 260-odd planets that have been discovered in other solar systems, Marcy and his team have found 150. His most recent discovery, announced last week, is a fifth planet orbiting a star called 55 Cancri, about 41 light-years from Earth. Marcy, 53, sat down in his office to talk about the friendly and not-so-friendly competition to find the first Earth-like planet that could harbor life.

Describe your latest discovery.

This is one of the nearest stars to our sun. It has nearly the same mass as our sun, the same temperature as our sun and the same age. Frankly, what’s delightful about it is that we now have five major planets orbiting it. The planets around 55 Cancri have a range of masses, from around 10 Earth masses at the smallest, to the largest, which is around four times as large as Jupiter. It’s certainly the largest complement of planets ever found around another star.

Are any of these planets habitable?


This newest planet, No. 5, resides in the habitable zone, about 0.8 Earth-sun distances from its star. So this new planet we’ve found would be warmed up -- like a face to a campfire -- to lukewarm temperatures, making the water, if any, liquid. Having said that, we suspect that this new planet is made mostly of hydrogen and helium gas. Its mass is about 55 times the mass of Earth. So it probably isn’t just a solid rock, like our Earth. Such a big planet with a rocky core and a fluffy gaseous envelope probably can’t support life as we know it.

How many planets have you discovered?

My team has discovered 150. The Swiss team is a strong second. In fact, I just got an e-mail from the leader of the team congratulating me on the five planets around 55 Cancri.

So the competition is friendly?


It’s a touchy friendship. We laugh about it. But in the true spirit of science we appreciate the competition because we know if we snooze, we will lose the next precious planets that are the next exciting batch to find.

What’s the allure of an Earth-like planet?

To find the first Earth was a dream of Aristotle. Even in the religious realm, people have wondered, and still do, whether Earth was uniquely put here. Not to delve into touchy issues, but there’s still a large -- how shall I put it -- spiritual question. Is the Earth the center of creation? And we’re about to find out whether there are any other Earths out there. The Vatican will be interested. It’s no joke. I’ve gotten two calls from them.

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