Twenty-Two Light Years Away, a Slim Hope for Life

Meet GJ 667Cc. GJ 667Cc is what’s known as a “Super-Earth,” a planet outside of our solar system (extrasolar) with a mass larger than Earth’s, but smaller than our solar system’s neighborhood gas giants. GJ 667Cc has a year that lasts a little less than a month (28.15 days) and is just over four times the size of Earth. It orbits a red dwarf star known as GJ 667C, which is a bit cooler and smaller than our Sun, itself a yellow dwarf. Because GJ 667C, actually part of a three star system, has a pretty different makeup than the Sun’s, it shines mostly in the infrared spectrum, rather than the visible.

In short, GJ 667Cc is nothing like Earth. But, according to a new paper to be published in The Astrophysical Journal Letters, this super-Earth is our current best bet for potentially habitable planets.

“This planet is the new best candidate to support liquid water and, perhaps, life as we know it," says the Carnegie Institute’s Guillem Anglada-Escude. GJ 667Cc actually replaces our old “Goldilocks planet” hope GJ 667Cb, which this same bit of research — conducted with help from a trio of powerful ground-based telescopes — confirmed was way too close to its star to support life, with a year of only about seven days. We don’t actually know much more about the new planet beyond its approximate mass and distance from its star. From that, we can infer the amount of solar energy that it receives and that it’s probably made of solid stuff. This, in the realm of new-Earth hunting, is great hope.

There is, of course, much, much more to be done before we can say anything more meaningful about the planet’s actual conditions. In an e-mail last night, Anglada-Escude explained further: “We don’t know that much. We have a very good measure of the period, a decent measurement of the mass (4 times Earth’s mass or more) but we know a lot from this star because it is nearby and it is a member of a triple system. Compared to other recent announcements, this candidate lies pretty well in the liquid-water habitable zone around this star, which is something the other proposed candidates with the RV method cannot say.” (RV method refers to the method of measuring changes in a star’s radial velocity in response to an orbiting planet; the star “wobbles” and we can infer the planet from this.)

We’ve been hearing a ton lately about habitable planets and Earth-like planets and super-Earths and one can imagine a reader being a bit weathered now by new planet announcements. Most all of those come from the wide-reaching Kepler project, which is constantly analyzing the light from 145,000 different stars. That is a vast amount of data and announcements come as the numbers are slowly crunched. The Carnegie work with GJ 667C is a bit different.

“Compared to the Kepler candidates, Kepler can measure sizes, but not masses, specially for these small worlds,” “Compared to the Kepler candidates,” Anglada-Escude says. “For example, Kepler 22b was announced to orbit within the HZ of a sun-like star. Still, only the size is known (not the mass), and with this radius it is most likely a Neptune like object.” (Neptune is a small version of a gas giant, an “ice giant.”

“Note that the habitable zone is defined precisely as: zone around the star where an Earth-like planet could support liquid water on its surface,” he continues. “None of these planets are Earth-like (nor even the new candidate). Note that you can have a gas giant in the habitable zone, but it doesn’t mean the gas giant is habitable. All this said, the new candidate is the best match to nominal definition of HZ, even though many aspects of the planet are still unknown.”

What’s next? All this is very exciting, yeah, but this announcement and others similar always seem like such a great tease. Twenty-two light years is still 22 light years. And, for our fastest current spacecraft, that’s about 93,000 years away. “Sending [a mission] nowadays is out of the question,” Anglada-Escude agrees. “It would be great though. I would suggest a planet imager-plus-spectrometer to survey all the stars within 10 parsecs (32.6 light years) is the next logical step. This way you would have a pretty good idea if there is something waiting for you out there. I am pretty sure there have to be even better candidates around more massive sun-like stars. (GJ 667C is red and low mass and some people argue this is not good for a life hosting planet.)”

That said, imagining a living planet adapted to infrared light in kinda fun.

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  Reach this writer at michaelb@motherboard.tv.