Super-Earth Gliese 1214b Has Water-Rich Atmosphere, Japanese Astronomers Say (light, Sun, solar)
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Super-Earth Gliese 1214b Has Water-Rich Atmosphere, Japanese Astronomers Say
Discovered in 2009 by the MEarth Project, this alien world is about 2.7 times Earth’s diameter and is almost 7 times as massive. It is located 42 light years away in the constellation Ophiuchus.
Dr Michitoshi Yoshida of Hiroshima University and his colleagues used the Suprime-Cam and the FOCAS optical camera aboard the Subaru Telescope to look for the Rayleigh scattering feature in the atmosphere of Gliese 1214b.
First, it is important to understand the significance of Rayleigh scattering. Rayleigh scattering of sunlight on Earth is what makes the Sun appear with a yellowish hue, and the sky appear blue during the day and red at sunset. It is the scattering of light by particles much smaller than the wavelength of the light.
Now lets take a closer look at the star:
Name...............: GJ 1214
Constellation......: Ophiuchus
Distance...........: 42.4012 Light Years (13 Parsecs)
Spectral Type......: M4.5
Radius.............: 150,228 km (0.2064 R☉)
Mass...............: 0.15 ± 0.011 M☉
Density............: 95.8 g/cm^3
Age................: 6 billion years
Life Expectancy....: 1.147 trillion years
Surface Temperature: 3026 ± 150 K
Radius.............: 0.216 ± 0.012 R☉
Metallicity [Fe/H].: 0.39 ± 0.15
The star GJ 1214 is a very small, low density, red dwarf with only 40% of the metallicity in its composition than Sol has. This would imply that any planets within the GJ 1214 solar system would also be of low density.
The planet is 2.7 times larger than Earth, and 6.6 times more massive. However, due to its very low density (Earth's Density = 5.52 g/cm^3) the surface gravity is just slightly less than Earth's gravity. Since the density of water is 1 g/cm^3, it would suggest that there is very little in the form of rock on this planet, and that the entire surface is covered by water.
However, if we take a closer look at the orbital characteristics of the planet, we get a surprise:
Semi-Major Axis: 0.0143 ± 0.0019 AU (2,139,250 km; 1,329,268 miles)
Eccentricity...: 0.135 ± 0.135
Orbital Period.: 1.5804 Days (38 Hours)
The planet is extremely close to its star. By comparison, the planet is 27 times closer to its star than Mercury is to Sol. The eccentricity could be anywhere from 0 (a perfect circle) to 0.27 (very elliptical). If we plot an orbit that is a perfect circle, the mean surface temperature of the planet would be about 196°C (384.8°F). However, since the planet is so close to its star it will be tidally locked. Meaning only one side of the planet will face its star at all times. The planet's day would be equal to its year. The dark side of the planet would be near freezing, and the day side of the planet would be much hotter than 196°C.
As a result, the proximity to its star makes it is extremely unlikely that there would be liquid water on the day side of the planet. It is also very likely that the dark side of the planet would be frozen. In this particular case I would say it is far more likely that the planet has huge amounts of water vapor with a lot of clouds in its atmosphere on the day side, that freezes and turns into snow on the dark side. This is consistent with a flat Rayleigh scattering effect, but it pretty much rules out the possibility of a water world. Liquid water may exist in the twilight region of the planet, the half-way point between the dark and light side of the planet, but it is not likely to exist anywhere else.
If one side is frozen and the other side to hot wouldn't there be a middle ground between the 2 sides where water would remain a liquid?
Yes, as I suggested:
Quote:
Originally Posted by Glitch
Liquid water may exist in the twilight region of the planet, the half-way point between the dark and light side of the planet, but it is not likely to exist anywhere else.
The huge difference in temperature between the day and night sides of the planet would also suggest extremely strong winds and violent weather patterns.
It's a shame we can only look from a distance and not hop over and check it out. Hopefully after this life we'll be able to check the universe out and all it offers.
Due to pressure, it could still be a water world with a thick water vapor atmosphere at those temperatures. The Density is a tad high to not have liquid water at the "surface". It is higher then Neptune's which is theorized to have a liquid mantle/surface of water and ammonia. Of course there could be considerably more rock at the core too, but I still think this would have liquid water around the rock.
Also, since it may have thick water atmosphere, it wouldn't surprise me if the overall temperature isn't more uniform across the planet. What that number is really depends on the solar radiation and if it is reflected or absorbed. It could barely be above boiling up to possibly considerably hotter then suggested (high 200 C).
Due to pressure, it could still be a water world with a thick water vapor atmosphere at those temperatures. The Density is a tad high to not have liquid water at the "surface". It is higher then Neptune's which is theorized to have a liquid mantle/surface of water and ammonia. Of course there could be considerably more rock at the core too, but I still think this would have liquid water around the rock.
Also, since it may have thick water atmosphere, it wouldn't surprise me if the overall temperature isn't more uniform across the planet. What that number is really depends on the solar radiation and if it is reflected or absorbed. It could barely be above boiling up to possibly considerably hotter then suggested (high 200 C).
You make a good point, at some depth there is going to be sufficient pressure to keep water in a liquid state. At the "surface" it may be at or above boiling on the day side of the planet, and frozen ice on the night side of the planet, but at some point beneath the "surface" on both sides of the planet liquid water may still be found.
The "surface" temperate was calculated using Stefan's law. Since this exoplanet is more like a small Neptune than a large Earth, I used the albedo for Neptune of 0.29 and an infrared emissivity of 0.75. Granted, since that information for the exoplanet is not currently available, it was entirely an educated guess on my part and may not have any bearing on reality. The overwhelming bulk of this star's radiation is going to be in the infrared rather than the ultraviolet end of the spectrum, given the spectral type. Stefan's law does not take this into account.
Since the exoplanet must be tidally locked at the distance it orbits its star, there must also be a twilight region, perhaps only a few degrees wide on either side of the planet, where it transitions from being extremely hot to being extremely cold. The temperature difference between the light and dark sides of the planet would certainly result in very strong winds which, as you suggest, may give the planet a more evenly distributed "surface" temperature. Also, as a result of being tidally locked, there would be no tides. Just two unmoving bulges on each side of the planet.
While I would not rule out the possibility of life on this planet entirely, it seems unlikely to have what we would consider to be "terrestrial" life. Given our limited understanding of how and where planets form, it does not seem possible that such a planet could form so close to its star. It may have formed further away and migrated toward its star after being perturbed in its orbit. If that were the case, then a more elliptical orbit (closer to 0.27 than 0.0 eccentricity) would seem likely. In which case the exoplanet's "surface" temperature could vary considerably during its 38 hour orbit.
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