In 2002, the discovery of the four Jupiter mass 55 Cancri d was announced in a paper that also confirmed the evidence for Planet b, which had been discovered in 1996. But when the signals of the two planets were removed from the radial velocity of 55 Cancri, a sharp peak remained, seeming to indicate a lower mass planet orbiting with a period of 44 days. But, this finding was suspect. The rotational period of the star itself was 35 to 42 days. The supposed planet's period seemed too similar to the star's period to be a coincidence, suggesting that the remaining peak might be the result of star spots or irregular rotation on the surface of 55 Cancri itself.
But, 55 Cancri is a quiet star, showing no signs of photospheric irregularities that could explain the peak. So, despite the suspiciousness of its period, 55 Cancri c was tentatively added to the list of extrasolar planets.
In 2004, the study that announced the discovery of Super Earth 55 Cancri e confirmed the existence of Planet c as well. It seems that the small gas giant, about a quarter the mass of Jupiter, truly does exist and that the similarity of its period to its star's rotation really is coincidental.
Analysis of the orbit of 55 Cancri c indicate that it may be in or near a 3:1 resonance with Planet b.
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 | 55 Cancri c
Especially at apastron, temperatures on 55 Cancri c may be cool enough to allow clouds to exist in parts of the atmosphere, but much of the planet would still be clear and rendered blue by Rayleigh scattering. Here we see the planet face on, its turbulent bands of clouds floating on a bottomless sea of blue. The clouds might be composed of sulfur compounds like those on Venus or, possibly, of water. |  | A Cratered Moon of 55 Cancri c
55 Cancri c's orbital distance and eccentricity make it possible that the planet has not yet been tidally locked by its parent star. If this is the case, it may have a retinue of moons, some of which may be as massive as Mercury. Here we see an airless and heavily cratered rocky moon with the blue planet beyond girdled in bands of white clouds. |  | 55 Cancri c Summer
At periastron, 55 Cancri c is not much further away from its star than 55 Cancri b, and the planet would heat up dramatically. As temperatures rise with the approach of summer, the planet's clouds disperse, leaving only a few lingering wisps at the poles. The majority of the planet's surface becomes blue and featureless, just like it's more massive sibling, Planet b. |  | Inner Worlds of 55 Cancri
55 Cancri b and c are closest when the two planets align with their sun while Planet c is at periastron. When this happens, the two planets are separated by only 0.015 AU. That's a little over two million kilometers, or about six times the distance from the Earth to the Moon. Here, we see an alignment of worlds, with 55 Cancri c and it's moon in the foreground. Beyond hangs 55 Cancri b, as well as the parent star itself with 55 Cancri e in transit across its disk. So close are Planets b and c that the inner world's night side is dimly lit by sunlight reflected from the outer. |  | 55 Cancri Double Transit
From orbit around 55 Cancri c, we zoom in on the two degree disk of the system's parent star, 0.2 AU away, and witness a rare double transit of the two inner planets.
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