An extrasolar planet, 55 Cancri f orbits the star 55 Cancri, some 45 light years from Earth in the Cancer (Crab) constellation.
Mass: 3.42 x 1026 kg
Composition: Unknown but likely to be a hydrogen and helium gas giant
Orbit: 259 Earth days around 55 Cancri
55 Cancri f was spotted in 2005 by astronomers at the University of California. It took until 2007, its official discovery date, before they could present their finding officially in peer-reviewed publications. 55 Cancri f was the first planet discovered outside the Solar System to orbit in a star’s habitable zone. This is a region along the orbit where liquid water would exist on any solid surface of the planet. Excluding the Sun, 55 Cancri became the first star known to support five or more orbiting planets.
Astronomers used the Shane telescope located at the Lick Observatory on Mount Hamilton just east of San Jose and at the W.M. Keck Observatory at Mauna Kea in Hawaii. It was the fifth planet discovered to be orbiting around 55 Cancri. The astronomers had been observing over 2,000 nearby stars and required over 320 velocity measurements to understand the signals emitted by each of the planets orbiting 55 Cancri. The observations continued for over 18 years before any extrasolar planets were identified by astronomers at any location in the Universe.
However, 55 Cancri f probably is not a habitable planet as it seems to be composed of gas and resembles gas giants such as Saturn. It may hold water vapour clouds around its surface.
55 Cancri f is the fourth closest of five planets orbiting its star. Its distance from the star is approximately 116.7 million kilometres. It is closer to its star than Earth is to the Sun, but the star itself is fainter than the Sun. Observations made by the Hubble Space Telescope show that the 55 Cancri planets have mostly circular orbits, though 55 Cancri f orbit may be slightly elliptical.
It remains unclear whether the planet has any moons. Gas giants of this kind in the Solar System have moons that may hold liquid water on a rocky surface. Astronomers believe that any moon orbiting around 55 Cancri f would not be detectable. Should one exist, it would have to be the size of Mars to have a mass sufficient to hold an atmosphere around it and liquid water on its surface.