Astronomers using the W.M. Keck Observatory on Mauna Kea have discovered a fifth planet orbiting a star in the constellation Cancer, a discovery that suggests multiplanet systems such as our own solar system may be common in the cosmos.

The newly discovered planet orbits the star 55 Cancri, a star about the same age and mass as our sun just 41 light years from Earth. Its five planets are the most ever detected orbiting a star outside of our own solar system, and the 55 Cancri system is so close to us, the star is easily seen using binoculars.

"The significance is marvelous, I think," said Geoffrey Marcy, an astronomer with University of California, Berkeley and a collaborator on the research. "We now know that our sun and its family of planets is not unusual. ... this discovery shows that our Milky Way contains billions of planetary systems, many of them as rich as our own solar system, and of course we strongly suspect that many of those planetary systems harbor ... Earth-like planets."

Planetary scientist Jonathan Lunine called the discovery an important step in the quest for what he called the "Holy Grail" — the discovery of a planet with a mass similar to that of Earth, orbiting a star like our sun, with an atmosphere likely to support life.

"It's a process that's going to take 10, 15 or 20 years to do both from the ground and from space, but for all we know, there may be Earth-sized planets around most solar-type stars, we simply can't see them yet," said Lunine, professor of planetary sciences and of physics at the University of Arizona.

The newfound planet is within what scientists consider the "habitable zone" around star 55 Cancri, an area where the temperature range could allow liquid water to pool, making it possible the planet could support life.

However, the mass of the newly discovered planet is about 45 times that of Earth, suggesting to astronomers this particular planet is surrounded by a large envelope of gases and high-pressure water that "seems to us to render the planet inhospitable for life as we know it," Marcy said.

Astronomers can't be sure about many details about the newly discovered planet, mostly because they cannot actually see it.

The planet was discovered using the "Doppler technique," in which astronomers detect planets and calculate their mass and other properties by measuring the wobble the planets cause in their host stars as the planets move through their orbits and exert a gravitational tug on the stars.

"We can only imagine that it might look something like a sort of a beefy Neptune-like planet, or perhaps a Saturn-like planet with rings and moons around it," said Debra Fischer, assistant professor of astronomy at San Francisco State University and lead author of a paper on the research, to be published in Astrophysical Journal.

The newly discovered planet is more massive than Uranus or Neptune, but is smaller than Saturn. It is the fourth-most-distant planet from 55 Cancri and completes its orbit around the star every 260 days.

The newfound planet orbits at about 72.5 million miles from 55 Cancri. By comparison, the Earth is about 93 million miles from the sun.

Astronomers have now discovered about 250 planets outside our solar system, and Fischer said she suspects there are more planets to be found orbiting 55 Cancri.

The most likely place to look would be the huge gap between the newly discovered planet and the outermost or fifth planet orbiting the star, she said. That outermost planet takes 14 years to complete one orbit around 55 Cancri.

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