In our galaxy, planets orbiting other stars may be the norm
Leading extraplanetary team says high-precision, spaceborne instruments will help advance the field of astrobiology

By Diane Ainsworth, Public Affairs

A newly discovered, Jupiter-like planet and its icy moon, the tiny orb in the right foreground, circle the star 55 Cancri 2002, seen in the distance in this artist’s rendering. Berkeley astronomers hope to find even smaller extrasolar planets as they search the skies in an effort to locate worlds capable of supporting life. Copyright 2002 Lynette Cook

09 October 2002 | The count is up to 102. That’s the number of giant planets, orbiting suns in other solar systems, that Berkeley planet-hunter Geoff Marcy and his colleagues have found over the last seven years. Marcy, who pioneered the technique for spotting planets the size of Jupiter tens to hundreds of light years away, has been finding them almost faster than he can report them.

He’s found them as close as 10.5 light years from Earth —about 63 trillion miles away, too far to be seen with even the most high-powered telescopes — and as far away as about 150 light years. “And there are probably five terrestrial-size planets” for every Jupiter-size planet he and his fellow collaborators find, he told a gathering of professional and amateur astronomers at the annual meeting of the Astronomical Society of the Pacific (ASP), held Sept. 28-29 on the Berkeley campus.

Pursuing the ‘Holy Grail’
Finding extrasolar planets is the first step toward finding planets that are hospitable to life now, or that could have been at some point in the past — the Holy Grail of astrobiology, which seeks to determine if life exists anywhere in or outside of the solar system. Now that the techniques are in place (they involve measuring the telltale signs of a planet’s presence, especially its gravitational pull on a star), Marcy and his colleagues are intent on pushing the technology to the limit, to achieve even more precision in their measurements. Only then will they be able to spot small planets the size of Earth, Mars, or Neptune.

As good fortune would have it, they will have new spaceborne instruments to use in the very near future. Orbiting coronagraphs, which can block out everything but a star’s corona and the light reflected by orbiting planets, are of particular interest. They believe they will be able to make some groundbreaking discoveries using these new instruments, perhaps spying small, rocky planets with atmospheres and oceans.

“This isn’t speculation anymore,” said Berkeley astronomer Alex Filippenko, ASP president for the past two years, about the existence of Earth-like planets in other solar systems. “The big guys exist, and it seems very reasonable to suppose that the little guys exist as well.”

Looking for extrasolar planets is one of the major themes of astrobiology. During two days of discussions about it, participants heard a range of opinions from some of the world’s most reputable astronomers and astrobiologists, including David Levy, discoverer of more than 21 comets and co-discoverer of comet Shoemaker-Levy 9, which slammed into Jupiter in 1994; Chris McKay, a planetary scientist at NASA Ames Research Center involved in planning for future manned missions to Mars; and Jill Tarter, director of the SETI Institute’s Center for SETI Research.

Also presenting their views were Seth Shostak, a leading astronomer with SETI, who discussed international protocol in the event that signals from an intelligent civilization are ever detected; Ben Zuckerman, a UCLA astronomer who believes the search for intelligent life elsewhere is futile because, if contact were going to be made, it would have happened by now; and Chris Impey, of the University of Arizona, who, while believing it likely that there is intelligent life elsewhere, remains pessimistic that we will ever have the technology to make contact over such vast distances.

Whether or not intelligent life exists in our galaxy or in others, astrobiology’s progress depends, in no small part, on the search for planets like our own outside of the solar system, a science that is still very much in its infancy.

Not quite there yet
“The technology isn’t yet good enough” to detect Neptunes or Plutos out there, Filippenko says. Still, it’s already begun to take Marcy and his colleagues star-hopping across the Milky Way, which is home to roughly 200 billion stars. Not bad for a first start — and there will be many more opportunities, because the Milky Way is a giant compared to other spiral galaxies. Some 100,000 light years across, it harbors, by Marcy’s estimate, at least 12 billion solar systems — most of which, given the laws of physics and chemistry, include planets probably not unlike the gaseous and terrestrial spheres of our own solar system.

About 3 percent of the stars Marcy and his colleagues plan to observe are likely to reveal Earthlike planets circling in a variety of orbits. While they hope to secure funding for a new, fully automated 2-meter telescope that will allow them to start a round-the-clock observation program from the UC-operated Lick Observatory, it’s a series of space missions planned for the next decade-plus that’s more likely to help them discover the extrasolar planets they believe are out there, too tiny and distant to detect from the ground. Next in the series is a spaceborne telescope called Kepler, which is expected to find scores of Earth-size planets and triple the number of known Jupiter-size planets after its scheduled launch in 2006.