Researchers Identify First Five-Planet Extrasolar System

November 12, 2007 / Posted by: Shige Abe

Extrasolar planet research supported by the NASA Astrobiology Institute and the National Science Foundation has yielded evidence of a fifth planet around the sun-like star 55 Cancri, making this system the first quintuple extrasolar planetary system ever discovered.

“The newly discovered planet weighs about 45 times the mass of Earth,” The Jet Propulsion Laboratory reported in a press release, “and may be similar to Saturn in its composition and appearance. The planet is the fourth from 55 Cancri and completes one orbit every 260 days. Its location places the planet in the ‘habitable zone,’ a band around the star where the temperature would permit liquid water to pool on solid surfaces. The distance from its star is approximately 116.7 million kilometers (72.5 million miles), slightly closer than Earth to our sun [.78 AU], but it orbits a star that is slightly fainter.”

University of California-Berkeley astronomer Geoff Marcy told reporters that 263 extrasolar planets have been detected thus far. In addition to this five-planet system, astronomers have identified one four-planet system and two three-planet systems. University of Arizona planetary Jonathan Lunine said this discovery is an indication of how extrasolar planet searching is shifting from finding lots of stars with single planets to finding multiple-planet systems.

A driving goal of extrasolar planet searching is to find an Earth-like planet around another star. Though this fifth planet of 55 Cancri is in its star’s habitable zone, it is not Earth-like. San Francisco State University astronomer Debra Fischer pointed out that the concept of a habitable zone in an extrasolar planetary system is still “a fuzzy idea” at this point. Scientists know how to predict the temperatures of the upper atmospheres of exoplanets, but they cannot yet tell other factors such as tidal heating by moons would affect the habitability of those planets. In the 55 Cancri system, another smaller, habitable, terrestrial planet might possibly be “lurking in the gap” between the newly identified fifth planet and its closest neighbor, according to Lunine – but that is for the next generation of planet detectors to determine, he noted. The planned SIM PlanetQuest mission could see Earth-like planets in habitable zones, said Marcy, and the planned Terrestrial Planet Finder could take the first pictures of Earth-like planets and determine their atmospheric composition. Meanwhile, astrobiology research will continue to contribute to better understanding of extrasolar planets – how they form, where to find them, what they might be like – and possibilities for life there.