Kepler 22B - Is life possible here?
Kepler-22b is a super-Earth that could be covered in a super ocean. The jury is still out on Kepler-22b’s true nature; at 2.4 times Earth’s radius, it might even be gaseous. But theoretically an ocean world tipped on its side – a bit like our solar system’s ice giant, Uranus – turns out to be comfortably habitable based on recent computer modeling. Researchers found that an exoplanet in Earth’s size range, at a comparable distance from its sun and covered in water, could have an average surface temperature of about 60 degrees Fahrenheit (15.5 Celsius). Because of its radical tilt, its north and south poles would be alternately bathed in sunlight and darkness, for half a year each, as the planet circled its star.
How Kepler 22b was found
Kepler 22-B
Star
Kepler 22
Transit method
Most known exoplanets have been discovered using the transit method. A transit occurs when a planet passes between a star and its observer. Transits within our solar system can be observed from Earth when Venus or Mercury travel between us and the Sun.
Transits reveal an exoplanet not because we directly see it from many light-years away, but because the planet passing in front of its star ever so slightly dims its light. This dimming can be seen in light curves – graphs showing light received over a period of time. When the exoplanet passes in front of the star, the light curve will show a dip in brightness.
This data is part of why transits are so useful: Transits can help determine a variety of different exoplanet characteristics. The size of the exoplanet’s orbit can be calculated from how long it takes to orbit once (the period), and the size of the planet itself can be calculated based on how much the star’s brightness lowered.
We can also learn about an exoplanet’s atmosphere during a transit. As it transits, some light will go through its atmosphere and that light can be analyzed to determine what different atmospheric elements influenced its particular dispersion. Atmospheric composition is important to determining habitability. Habitability can be further shown through orbital size and star temperature. These help determine the temperature of the planet itself, thus telling us whether its surface is a comfortable temperature or unsuitable for life.
Discovered
The planet's first transit was observed on 12 May 2009. Confirmation of the existence of Kepler-22b was announced on 5 December 2011.
It was discovered by NASA's Kepler Space Telescope in December 2011 and was the first known transiting planet to orbit within the habitable zone of a Sun-like star, where liquid water could exist on the planet's surface. Kepler-22 is too dim to be seen with the naked eye.
Mass radius and temperature
Kepler-22b's radius is roughly 2.4 times that of Earth. Its mass and surface composition remain unknown, with only some very rough estimates established: it has fewer than 124 Earth masses at the 3-sigma confidence limit, and fewer than 36 Earth masses at 1-sigma confidence. The adopted model in Kipping et al. (2013) does not reliably detect the mass (the best fit is 52.8 MEarth).
Kepler-22b, dubbed by scientists as a 'water world', might be an 'ocean-like' planet. It might also be comparable to the water-rich planet Gliese 1214 b although Kepler-22b, unlike Gliese 1214 b, is in the habitable zone. An Earth-like composition is ruled out to at least 1-sigma uncertainty by radial velocity measurements of the system. It is thus likely to have a more volatile-rich composition with a liquid or gaseous outer shell; this would make it similar to Kepler-11f, the smallest known gas planet.
Natalie Batalha, one of the scientists on the Kepler Space Telescope project, has speculated, "If it is mostly ocean with a small rocky core, it's not beyond the realm of possibility that life could exist in such an ocean". This possibility has spurred SETI to perform research on top candidates for extraterrestrial life.
In the absence of an atmosphere, its equilibrium temperature (assuming an Earth-like albedo) would be approximately 262 K (−11 °C), compared with Earth's 255 K (−18 °C).
Host Star
The host star, Kepler-22, is a G-type star that is 3% less massive than the Sun and 2% smaller in volume. It has a surface temperature of 5,518 K (5,245 °C; 9,473 °F) compared with the Sun, which has a surface temperature of 5,778 K (5,505 °C; 9,941 °F). The star is about 4 billion years old. In comparison, the Sun is 4.6 billion years old.
The apparent magnitude of Kepler-22 is 11.5, which means it is too dim to be seen with the naked eye.
Habitability
The average distance from Kepler-22b to its host star Kepler-22 is about 15% less than the distance from Earth to the Sun[2] but the luminosity (light output) of Kepler-22 is about 25% less than that of the Sun. This combination of a shorter average distance from the star and a lower stellar luminosity are consistent with a moderate surface temperature at that distance, if it is assumed that the surface is not subject to extreme greenhouse heating. If Kepler-22b moves in a highly elliptical orbit, its surface temperature variance will be very high.
Climate
Scientists can estimate the possible surface conditions as follows:
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In the absence of an atmosphere, its equilibrium temperature (assuming an Earth-like albedo) would be approximately 262 K (−11 °C), compared to Earth's 255 K (−18 °C).
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If the atmosphere provides a greenhouse effect similar in magnitude to the one on Earth, it would have an average surface temperature of 295 K (22 °C).
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If the atmosphere has a greenhouse effect similar in magnitude to the one on Venus, it would have an average surface temperature of 733 K (460 °C).
Recent estimates suggest that Kepler-22b has more than a 95% probability of being located in the empirical habitable zone defined by the recent Venus and early Mars limits (based on estimates of when these planets may have supported habitable conditions), but less than a 5% chance of being located in the conservative habitable zone within the Circumstellar habitable zone, (estimated from a 1D cloud-free radiative-convective model).
Limits on satellites
The Hunt for Exomoons with Kepler (HEK) project has studied the Kepler photometry of the planet, to find any evidence of transit timing and duration variations that may be caused by an orbiting satellite. Such variations were not found, so ruling out the existence of any satellites of Kepler-22b with a mass greater than 0.54 Earth masses.
Art and Comparison
A diagram of the Kepler-22b System, compared to our Inner Solar System.