SYDNEY: Astronomers have detected a fifth extrasolar planet circling 55 Cancri, a star 41 light years away. This is the greatest number of confirmed planets yet found orbiting another star.
"This discovery of the first ever quintuple planetary system has me jumping out of my socks," said Geoff Marcy an astronomer at the University of California, Berkeley in the USA. "The significance is marvellous. We now know that our Sun and its family of planets is not unusual."
Liquid water?
55 Cancri is located 41 light-years away in the constellation Cancer and has nearly the same mass and age as our Sun (it is easily visible with binoculars from Earth). The researchers discovered the fifth planet using the Doppler technique, in which a planet's gravitational tug is detected by the wobble it produces in the parent star.
It weighs about 45 times the mass of Earth and may be similar to Saturn in its composition and appearance. It is the fourth planet out from 55 Cancri and completes one orbit every 260 days.
The researchers have also discovered that the planet's location places it in the habitable zone: a band around the star where the temperature permits liquid water to exist – and therefore renders the discovery of life more likely. Though its orbit is slightly closer than Earth's is to our Sun, its star is slightly fainter.
"The gas-giant planets in our Solar System all have large moons," said Debra Fischer, an astronomer at San Francisco State University in California and lead author of a paper on the find upcoming in the Astrophysical Journal. "If there is a moon orbiting this new, massive planet, it might have pools of liquid water on a rocky surface," she said.
Fischer and Marcy are part of a team that discovered this planet after careful observation of 2,000 nearby stars with a telescope at California's Lick Observatory and the Keck Observatory on Mauna Kea, Hawaii. More than 320 velocity measurements were required to disentangle signals from each of the planets.
Family of planets
The planets around 55 Cancri are somewhat different from those orbiting our Sun. The innermost planet is believed to be about the size of Neptune and whips around the star in less than three days at a distance from the star of approximately 3.5 million miles. The second planet is a little smaller than Jupiter and completes one orbit every 14.7 days, at a distance from the star of approximately 11.2 million miles. The third planet, similar in mass to Saturn, completes one orbit every 44 days at a distance from the star of approximately 22.3 million miles.
The fifth and most distant known planet is four times the mass of Jupiter and completes one orbit every 14 years at a distance from the star of approximately 539.1 million miles. It is still the only known Jupiter-like gas giant to reside as far away from its star as our own Jupiter.
"Discovering these five planets took us 18 years of continuous observations at Lick Observatory, starting before any extrasolar planets were known anywhere in the universe," said Marcy. "But finding five extrasolar planets orbiting a star is only one small step. Earth-like planets are the next destination."
"This work marks an exciting next step in the search for worlds like our own," commented Michael Briley, an astronomer at the U.S. National Science Foundation. "To go from the first detections of planets around sun-like stars to finding a full-fledged solar system… in just 12 years, is an amazing accomplishment and a testament to the years of hard work put in by these investigators."
with NASA
