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In recent years, the search for an Earth-like planet orbiting another star has been the most exciting in science. The world has waited with baited breath for the discovery of another Earth.


But the discovery of Earth 2.0 has been a damp squib. Not because astronomers haven’t found one; on the contrary! The problem is they’ve found too many candidates. And these have turned out to be so unlike Earth that it’s hard to imagine that any of them can be a convincing twin.

We’re left, like the starving donkey equidistant between two bails of hay, unable to decide on what to celebrate.

The top candidates so far are these:

Gliese 4581 g, the fourth rock from a red dwarf some 20 light years from Earth in the constellation of Libra

GJ 1214 b, a sub-Neptune-sized planet orbiting a star in the constellation of Ophiucus 40 light years away

and HD 28185 b, a gas giant in a near circular orbit that is entirely within the habitable zone of a Sun-like star in the constellation of Eridanus. This planet’s moons, if it has any, may be good candidates for ‘other Earths’

Today, we can add another strange planet to the list: 55 Cancri f, one of five planets known to orbit an orange dwarf star some 40 light years away in the constellation of Cancer.

Kaspar von Braun at the California Institute of Technology in Pasadena and a few pals have measured its orbit accurately for the first time. These guys are able to confirm that 55 Cancri f is a genuine candidate to support liquid water.

They say that although this planet’s orbit is much more elliptical than Earth’s, it still spends most of its time (74 per cent) in the habitable zone.

Furthermore, 55 Cancri f is quite like Earth in some ways. Its year is about the same length as ours. And with moderate greenhouse warming, it could support liquid water all year round.
But unlike Earth, its mass is about the same as Neptune’s (although it doesn’t seem to have a large gaseous atmosphere).

And one other thing. it has two suns! This system consists of an orange dwarf star with a companion red dwarf that orbits at a distance of about 1000 AU. 55 Cancri f is part of a binary star system.

That’s weird! The sky on Cancri 55 f must be out of this world. For one half of the year, red and orange suns would light the daytime sky. Then, at night, the red dwarf would be visible for half the year and distant stars only visible for the other half.

That makes Cancri 55 f, if not the most promising exo-Earth, then at least the most exotic.

Ref: arxiv.org/abs/1107.1936: The 55 Cancri System: Fundamental Stellar Parameters, Habitable Zone Planet, and Super-Earth Diameter

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