Kepler-22b was the first exoplanet ever discovered lying inside its parent star’s habitable zone.
It was discovered by the now-retired Kepler Space Telescope and, at the time, was an incredible discovery.
That was back in 2011, but the exoplanet still represents one of our best chances of discovering live elsewhere in the Universe.
A brief history of exoplanet science
These days, of course, we take exoplanets for granted.
With over 5,700 exoplanets fully confirmed and thousands of other candidates awaiting further study, we talk glibly about what their atmospheres are like and whether they’d be capable of supporting Earth-like lifeforms.
Sometimes forgetting, perhaps, that the first confirmed exoplanet wasn’t spotted until 1992, a mere 32 years ago.
The existence of other planets had long been mooted, of course, but we had no concrete proof of their existence.
For all we knew, the (then) nine planets of our own Solar System were the only ones in the entire Universe!
It’s crazy to think that an idea which seems risible now is actually what many of us (those of us aged over 45 or so, anyway) were taught in schools.
Kepler-22b discovery
It's fair to say that the 1992 discovery of a planetary system around the pulsar PSR B1257+12 caused quite a stir.
Nearly two decades later, the discovery of Kepler-22b would have an equally big impact, due to its ‘Goldilocks’ location.
Very simply, if a planet’s too close to its parent star, it’s too hot for life to exist because water (an essential component of life as we currently understand it ) would boil away; if it’s too far away, it’s too cold and water would freeze.
In-between those two extremes lies the ‘Goldilocks’ or habitable zone, where it’s neither too hot nor too cold.
And it was in the habitable region around the Sun-like star Kepler-22 that, in December 2011, astronomers spotted a planet whose radius is just 2.1 times that of our own Earth, putting the planet in the ‘super-Earth’ category, much like Kepler-452b.
Is Kepler-22b a habitable planet?
Given that Saturn, for instance, has a radius that’s 9.5 times that of Earth, that makes Kepler-22b – a roughly Earth-sized planet, orbiting a Sun-like star at an orbital distance that puts it within the star’s habitable zone – about as Earth-like an exoplanet as science has turned up so far.
Kepler 22-b lies about 15% closer to its parent star than Earth does to the Sun, which would make it significantly hotter, were it not balanced out by the fact that host star Kepler-22 shines 25% less brightly than the Sun.
Scientists believe Kepler-22b to be a ‘water world’ similar to the exoplanet Gliese 1214 b, with substantial quantities of water in the form of surface oceans.
In that case, life could well be present in such oceans – though other astronomers have suggested Kepler-22b could instead be a ‘gas dwarf’ similar to exoplanet Kepler-11f.
