Extraterrestrial Jupiter

Today astronomers announced the discovery of more than a dozen new planets orbiting distant stars. One of those planetary systems looks a bit like our own.

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June 13, 2002: After 15 years of looking, a top planet-hunting team has finally found a distant planetary system that reminds them of home.

Geoffrey Marcy, astronomy professor at the University of California, Berkeley, and astronomer Paul Butler of the Carnegie Institution of Washington today announced their discovery of a Jupiter-like planet orbiting a Sun-like star at nearly the same distance as the real Jupiter orbits our own Sun.

Above: No one knows how the 55 Cnc system would look to the human eye, but space-artist Lynette Cook has imagined it. This digital painting shows, in the distance, the star with its two innermost planets. In the foreground is a hypothetical moon orbiting a Jupiter-like outer planet.

Astronomers had found Jupiter-like planets around other stars before. But they were all very close to their parent suns (astronomers called the planets "hot Jupiters") and their orbits were elongated -- not circular. "This new planet orbits as far from its star as our own Jupiter orbits the Sun,'' said Marcy. That's what makes it interesting.

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The star, 55 Cancri in the constellation Cancer, was already known to have one planet, announced by Butler and Marcy in 1996. That planet is a gas giant slightly smaller than the mass of Jupiter. It whips around the star in 14.6 days at a distance of only 0.1 AU. (AU means "astronomical unit." It's the distance between Earth and the Sun -- approximately 93-million miles. So, the first planet found in the 55 Cancri system is only one-tenth as far from its star as Earth is from the Sun.)

The newfound planet, announced today, orbits 55 Cancri at 5.5 AU, comparable to Jupiter's distance from our Sun of 5.2 AU. Its slightly elongated orbit takes it around the star in about 13 years, comparable to Jupiter's orbital period of 11.86 years. It is 3.5 to 5 times the mass of Jupiter.

The star 55 Cancri is 41 light years from Earth and is about 5-billion years old -- about the same age as our own Sun.

Below: This graphic compares the architecture of our own solar system with that of 55 Cancri. See also a related animation from JPL. [more]

"We haven't yet found an exact solar system analog, which would have a circular orbit and a mass closer to that of Jupiter. But this shows we are getting close, we are at the point of finding planets at distances greater than 4 AU from the host star," said Butler. "I think we will be finding more of them among the 1,200 stars we are now monitoring."

The team shared its data with astronomer Greg Laughlin at the University of California, Santa Cruz. His dynamical calculations show that an Earth-sized planet could survive in a stable orbit between the two gas giants. For the foreseeable future, existence of any such planet around 55 Cancri will remain speculative.

"This planetary system will be the best candidate for direct pictures when the Terrestrial Planet Finder is launched later this decade," added UC Berkeley astronomer Debra Fischer.

Marcy, Butler, Fischer and their team also announced a total of 13 new planets today, including the smallest ever detected: a planet circling the star HD49674 in the constellation Auriga at a distance of .05 AU, one-twentieth the distance from Earth to the Sun. Its mass is about 15 percent that of Jupiter and 40 times that of Earth. This brings the number of known planets outside our solar system to more than 90.

Editor's Note: The work described in this story was funded in part by NASA and the National Science Foundation. Discovery of a second planet orbiting 55 Cancri culminates 15 years of observations with the 3-meter (118-inch) telescope at Lick Observatory, owned and operated by the University of California. The team also includes Dr. Steve Vogt, UC Santa Cruz; Dr. Greg Henry, Tennessee State University, Nashville; and Dr. Dimitri Pourbaix, the Institut d'Astronomie et d'Astrophysique, Universite Libre de Bruxelles.

PlanetQuest -- (JPL) a great place to learn how astronomers search for distant planets. Includes an animation of the 55 Cnc system.

Exoplanets.org -- The home page for planet hunters Dr. Geoffrey Marcy (University of California, Berkeley) and Dr. Paul Butler (Carnegie Institution of Washington).

"The existence of analogs to our solar system adds urgency to missions capable of detecting Earth-sized planets - first the Space Interferometry Mission and then the Terrestrial Planet Finder," said Dr. Charles Beichman, NASA's Origins Program chief scientist at the agency's Jet Propulsion Laboratory.

Right: Future telescopes will use a technique called interferometry to cancel out the bright light from stars, which can hide dimmer planets in orbit around them.

In Search of ET's Breath -- (Science@NASA) Advanced space telescopes might soon probe far-off worlds for the chemical signatures of alien life.