George Dvorsky in io9:
Kepler 452b is located 1,400 light-years from our Sun. It weighs in at a hefty five Earth-masses and features a radius about 1.63-times larger than Earth’s. Technically speaking, that makes it a super-Earth, which is defined as an exoplanet with a mass between two- and ten-times that of Earth.
This possibly rocky planet orbits its G2 host star—the same type as ours—every 384 days, which is the longest orbital period of any small, transiting exoplanet observed to date. (“Small,” in this context, refers to a planet with a diameter less than two Earth-radii). The astronomers aren’t completely sure it’s a terrestrial planet, however, assigning a confidence level between 49% to 62%. There’s a distinct possibility, therefore, that Kepler 542b is more like a mini-Neptune than another Earth, which would reduce its odds of harboring life—or life as we know it—to basically zero.
Its host star is about 10% bigger than ours, and features an effective temperature of approximately 5,757 Kelvin (5,483 degrees Celsius). Kepler 542b is situated about 5% farther from its star than Earth, but receives about 10% more energy. It likely features a thicker atmosphere and cloud cover, and active volcanoes on its surface. Stellar evolution models place the age of the host star at 6-billion years, plus or minus a couple of billion.
As noted by the Kepler researchers at the press conference yesterday, “It’s the closest thing that we have to the planet Earth,” adding that it “receives roughly the same amount of energy, and with a star that’s a bit older and brighter.”
But is it Habitable?
Probably not—but it’s not an impossibility. Breathless talk of Kepler 452b being “Earth 2.0” or “Earth’s twin” tends to overlook the differences between the two planets (the possibility that it is actually a small gas planet, for example). That said, it has a number of things going for it that are intriguing, from an astrobiological perspective.