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Star's Habitable Zone Includes Possible Giant Earth

A planet at least seven times as massive as Earth orbits comfortably in the habitable zone of the star HD 40307. John Matson reports

It’s not quite a spitting image of Earth, but a newfound planet just might be similar enough to support life.

The world is one of three tentatively identified new exoplanets orbiting the star HD 40307. The outermost planet, HD 40307 g, orbits comfortably in the habitable zone, where Earth-like temperatures are possible. That means HD 40307 g could have liquid water on the surface—a probable prerequisite for life. The research is in the journal Astronomy & Astrophysics. [Mikko Tuomi et al., Habitable-zone super-Earth candidate in a six-planet system around the K2.5V star HD 40307]

But the planet is at least seven times as massive as Earth. So it could be a supersize version of our planet. Or it might be a scaled-down Neptune. A mini-Neptune would lack a solid surface and probably would not be an ideal habitat for life.

The star in question was already known to host three planets, so the total could reach six if the new finds are independently confirmed.

Confirmation is hardly assured. Two years ago some of the same astronomers involved in this work said they had located a potentially habitable planet called Gliese 581 g. But other researchers disputed the finding, and that planet’s existence has been in limbo ever since. As usual, more data should settle the argument.

—John Matson

[The above text is a transcript of this podcast.]

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