Gliese 777A B is more like our own system's Jupiter than any other planet so far discovered. It was the first giant planet of Jupiter mass discovered orbiting more than 3 AU from a sun-like star without any closer giant companions. This makes the Gliese 777A a prime hunting ground for earth mass planets closer in. Unlike the legions of Hot Jupiters and eccentric planets found around other stars, this planet reminds us of home.
When originally discovered, Gliese 777A B's orbit appeared to be close to circular, like Jupiter's, and it's mass is only a little greater than Jupiter's. More recent observations indicate that this world is actually highly eccentric. However, Gliese 777 A B still has much in common with Jupiter. Although it's orbital distance is over an AU closer than Jupiter, at 4.8 AU it is still well outside the star's habitable zone. The calculated temperature of the planet is almost identical to that of Jupiter, so its moons, some possibly as large as Mercury, would likely have icy surfaces with rocky cores. The planet itself would be girdled in white clouds of ammonia with, perhaps, clouds of water ice at lower depths. Like Jupiter and Saturn, these clouds would be stained with brown, yellow, and red hues created by the alchemy of trace gases in the sun lit upper atmosphere. Seasonal variations would driven both by the planet's axis tilt, if it is significant, as well as the planet's eccentic orbit. What's more interesting than the planet itself, however, is the lack of giant planets closer in. Other planets have been found at Jupiter-like distances from their stars, but none have been found without closer siblings. Certainly, if a another gas giant orbited closer to Gliese 777A, it would have been easier to detect than Planet b, and we would already know about it. But, no such planet has been found. The lack of a closer sibling means it is possible that one or more smaller terrestrial planets may exist. If one of these rocky worlds orbits within the star's habitable zone, then Gliese 777A may host a twin Earth as well as a twin Jupiter. There is mounting evidence that Jupiter is vital to life on Earth. Like our moon, it appears to serve as an asteroid deflection system, gobbling up or deflecting worldlets that might otherwise impact our planet. If a twin Earth does orbit Gliese 777A, then Planet b may provide a similar service. Gliese 777A is nearly seven billion years old, two billion years older than the sun. If the star does host an Earth-like world where life is possible, it has probably already evolved. What's more, there has been plenty of time for that life to evolve intelligence. But the possibility does not make it so, and time alone cannot give birth to a technical civilization. At 50 light years away, the Gliese 777A system is already awash in radio signals from Earth. In all likelihood, no one is there to hear those signals. Even if the system does host an Earth twin, life there may never have evolved beyond it's most simplest forms, if at all. And, even if intelligence arose there sometime in the last two billion years, that intelligence has, in all probability, already gone extinct. Are our calls falling on the deaf ears of a civilization dead for eons? Or, in coming decades, will our calls will be answered from the direction of an aging yellow star in the constellation of Cygnus?
View a VRML model of the system. Please be patient while the file downloads. For a VRML tour of our galaxy's exoplanets, check out Extrasolar VR.
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