Well, what does “Earth-like” mean? In this case, it means only that the planet is within a factor of 2.4 in radius of Earth and is in the “habitable zone” (that is, an orbit able to sustain liquid water) of a Sun-like star (implicitly defined in this case as within about ±25% of the Sun’s radiance). So given the incredibly broad definition of “Earth-like” being used in this case, our solar system already contains three Earth-like planets.
But do all three of those have temperatures of 72 degrees F?
Read the news carefully. Kepler-22b theoretically could have a temperature of 72 degrees F, sure . . . if it has an Earth-level greenhouse effect. But we don’t have any measurements of its temperature, and we don’t know the thickness or composition of its atmosphere.
Kepler-22b could have wound up with a Venus-type atmosphere, much thicker than Earth’s and high in carbon dioxide, and have a temperature far, far above 72 degrees F. It might have lost its atmosphere due to some early event and have radical temperature changes around the estimated −11 degrees C average. It might have an atmosphere that is thick and convective but transparent to infrared, with high albedo in the visible range, which results in it being an even-temperature ball even cooler than the no-atmosphere estimates make.
And that’s just atmospheric effects. Earth-type atmosphere combined with Venus-type or Moon-type rotation leaves you with an average of 72 degrees F, sure . . . but every spot alternately freezing and baking.
All “Earth-like” means in reference to Kepler-22b is that it’s within a factor of 2.4 in radius of Earth and is in the “habitable zone” (that is, an orbit able to sustain liquid water ore not depending on the local planetary characteristics) of a Sun-like star (implicitly defined in this case as within about ±25% of the Sun’s radiance). And by that definition, Venus and Mars both qualify as “Earth-like”.
But do all three of those have temperatures of 72 degrees F?
Read the news carefully. Kepler-22b theoretically could have a temperature of 72 degrees F, sure . . . if it has an Earth-level greenhouse effect. But we don’t have any measurements of its temperature, and we don’t know the thickness or composition of its atmosphere.
Kepler-22b could have wound up with a Venus-type atmosphere, much thicker than Earth’s and high in carbon dioxide, and have a temperature far, far above 72 degrees F. It might have lost its atmosphere due to some early event and have radical temperature changes around the estimated −11 degrees C average. It might have an atmosphere that is thick and convective but transparent to infrared, with high albedo in the visible range, which results in it being an even-temperature ball even cooler than the no-atmosphere estimates make.
And that’s just atmospheric effects. Earth-type atmosphere combined with Venus-type or Moon-type rotation leaves you with an average of 72 degrees F, sure . . . but every spot alternately freezing and baking.
All “Earth-like” means in reference to Kepler-22b is that it’s within a factor of 2.4 in radius of Earth and is in the “habitable zone” (that is, an orbit able to sustain liquid water ore not depending on the local planetary characteristics) of a Sun-like star (implicitly defined in this case as within about ±25% of the Sun’s radiance). And by that definition, Venus and Mars both qualify as “Earth-like”.