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View Full Version : Which Earth-like planet that has been discovered is most like Earth?



Plat
2013-Dec-11, 02:59 AM
????

Selfsim
2013-Dec-11, 06:44 AM
Unknown.

We don't know whether any of them have life, therefore we can make no comparative estimates with Earth, in order add emprical meaning to 'Earth-likeness'.
:)
(Chuckle, chuckle ..)

Selfsim
2013-Dec-11, 07:09 AM
Of course, there are those who would say Gliese 667Cc (http://en.wikipedia.org/wiki/Gliese_667C_c), currently ranked as 85% similar to earth (going by the Earth Similarity Index) (http://en.wikipedia.org/wiki/Earth_Similarity_Index), would be the prime contender ...
:)

solarsystem
2013-Dec-11, 09:49 AM
Kepler-22, it consists water and the most earth like planet ever discovered. It is 2.4 times the size of Earth.

eburacum45
2013-Dec-13, 08:01 PM
Kepler-22, it consists water and the most earth like planet ever discovered. It is 2.4 times the size of Earth.
Kepler 22b would not be very Earth-like at all, assuming that is the planet you mean; it has a mass of 6.36 Earth masses and is probably a water world, with an ocean about a hundred kilometers deep covering a high=pressure ice mantle. No land at all for life to develop on.

Gliese 667 Cc has a mass between 4.54 - ~9 x Earth, is also probably a waterworld, and probably pretty warm as well. Basically we haven't found any planet that resembles Earth in any meaningful way.

KABOOM
2013-Dec-13, 08:25 PM
Kepler 22b would not be very Earth-like at all, assuming that is the planet you mean; it has a mass of 6.36 Earth masses and is probably a water world, with an ocean about a hundred kilometers deep covering a high=pressure ice mantle. No land at all for life to develop on.

Gliese 667 Cc has a mass between 4.54 - ~9 x Earth, is also probably a waterworld, and probably pretty warm as well. Basically we haven't found any planet that resembles Earth in any meaningful way.

How is it determined that these larger Earth-like planets are likely "waterworlds"?

ravens_cry
2013-Dec-14, 06:44 AM
Mass verses volume I would imagine.

eburacum45
2013-Dec-14, 09:40 AM
How is it determined that these larger Earth-like planets are likely "waterworlds"?
These larger planets have much larger surface gravity conditions, so are likely to hang on to water more readily. If Venus were significantly larger it would have retain water and be a waterworld, or at least a large, hot Earth-like world.

But it is possible to imagine a large, relatively dry Earth-like superterrestrial, with partial ocean cover just like the Earth; what would that be like? Turns out that drier planets have even higher surface gravity than waterworlds - if Gliese 667 Cc has both continents and oceans, and has a mass of 4.54 x Earth (the lower limit) the diameter would be 19790 km (1.5x Earth) and the gravity 1.89 gees - much higher than our world, making the planet quite unEarth-like. Hydrogen would escape very slowly, which is why these large worlds would almost always be very wet.

Noclevername
2013-Dec-14, 03:02 PM
Of course, there are those who would say Gliese 667Cc (http://en.wikipedia.org/wiki/Gliese_667C_c), currently ranked as 85% similar to earth (going by the Earth Similarity Index) (http://en.wikipedia.org/wiki/Earth_Similarity_Index), would be the prime contender ...
:)


Kepler-62e has the highest Earth Similarity of confirmed exoplanets at 0.83, while Kepler candidate KOI-1686.01, if confirmed, would likely have an ESI of 0.89. Further, the candidate exomoon HD 222582 b m of a confirmed exoplanet, and several candidate exomoons (KOI 375.01 m, KOI-2933.01 m, KOI-422.01 m) of unconfirmed exoplanets, all have an ESI of 0.86.[1]


The following planets have been determined to have higher ESI than Venus or Mars:


KOI-1686.01 0.89 Unconfirmed[1]
Kepler-62e 0.83
Gliese 667C c 0.82
Gliese 581 g 0.82 Unconfirmed


Hmm, Gliese 667C c is similar but not 85% similar.

I wonder how much being a moon would affect surface conditions WRT water? Excess liquid water would probably get pulled off by tides, but IIRC many large moons in the Solar System have a gas torus which returns some gas, dust and vapor pulled off by the primary's tidal influence.

Selfsim
2013-Dec-15, 06:15 AM
Hmm, Gliese 667C c is similar but not 85% similar.At their last update (Dec 5th, 2013), the PHL Lab at Arecibo (http://phl.upr.edu/projects/habitable-exoplanets-catalog/data) has Gliese667Cc as having an Earth Similarity Index (ESI) of 0.84, and Kepler 62e at 0.83 (as you say). (Their rankings are focused on Habitability).

ESI is defined by them as:
The ESI or the "easy scale," measures how similar are planets to Earth in a scale from zero to one, with one being identical to Earth. ESI values between 0.8 and 1.0 correspond to Earth-like planets with a rocky composition that is able to hold a terrestrial atmosphere under temperate conditions. The ESI is a function of the planet's radius, density, escape velocity, and surface temperature.

If unconfirmed Kepler Candidates are taken into consideration, (according to them), KOI-4742.01, (a K-Warm Superterran) would have an ESI of 0.91 and would 'rule the roost'.

KOI-1686.01's ESI would be 0.89, (as you say).

TheBrett
2013-Dec-18, 06:05 PM
I'm going to go with Kepler-62f. It has a radius 1.4 times that of Earth, so the mass if it had Earth-like density would be on the order of 2-3 Earth masses (meaning it's probably not a gas dwarf). It orbits a high K-class main sequence star at a reasonable orbit with little eccentricity.

The only real downside is that it only gets about 42% of the sunlight intensity that Earth would get by comparison. That's more than Mars gets (36%), but still significantly less than Earth. I don't see that as a problem provided the atmosphere didn't freeze out early in the planet's history when the star was cooler, since a larger planet like that is likelier to retain heat and hopefully have active geology and a thick atmosphere to make up for the reduced sunlight.

Of course, that means that if it was Earth-like, it wouldn't really be "habitable" to us. It would probably have higher CO2 to keep it warm, high enough that we couldn't safely breath its atmosphere if we were on it.

Noclevername
2013-Dec-18, 06:08 PM
Of course, that means that if it was Earth-like, it wouldn't really be "habitable" to us. It would probably have higher CO2 to keep it warm, high enough that we couldn't safely breath its atmosphere if we were on it.

Instead of CO2, more water vapor or some more tolerable greenhouse gas could give it a bit more warmth. It could then have habitable climate areas, just less of them than Earth.

pincerssocks
2013-Dec-23, 06:18 AM
I also would like to know which Earth-like planet that has been discovered is most like Earth. If any of these earth like planet is habitable, I would love to live there. LOL

Noclevername
2013-Dec-23, 05:47 PM
I also would like to know which Earth-like planet that has been discovered is most like Earth. If any of these earth like planet is habitable, I would love to live there. LOL

Even the most Earthlike found so far is not very Earthlike. And Earthlike does not mean human-habitable; we have no way to determine that at present. There could be subtle toxins or conditions that we just can't detect from light-years away.

ravens_cry
2013-Dec-25, 10:56 PM
If it's too much like Earth, it might even be more dangerous, as the local diseases just might have a chance to latch on and make quick work of us, like measles and syphilis to the pre-Colombian inhabitants of the Americas.

Noclevername
2013-Dec-25, 11:27 PM
If it's too much like Earth, it might even be more dangerous, as the local diseases just might have a chance to latch on and make quick work of us, like measles and syphilis to the pre-Colombian inhabitants of the Americas.

That's not about the planet IMO, but the life that grows on it. It seems unlikely to me that even if we do find exolife, we'd ever encounter anything that biocompatible with Earth life. We may get some form of disease that can survive in us long enough to do harm, and some native life may be toxic to ingest, but measles and syphilis and things like smallpox, are viruses which are co-evolved parasites specifically adapted to certain hosts.

Jens
2013-Dec-26, 05:08 AM
Kepler 22b would not be very Earth-like at all, assuming that is the planet you mean; it has a mass of 6.36 Earth masses and is probably a water world, with an ocean about a hundred kilometers deep covering a high=pressure ice mantle. No land at all for life to develop on.

Out of curiosity, do we know for sure that life on earth developed on the land and not in water?

Trakar
2013-Dec-26, 06:00 AM
Which Earth-like planet that has been discovered is most like Earth? ????

Venus

Barabino
2013-Dec-26, 07:44 AM
Out of curiosity, do we know for sure that life on earth developed on the land and not in water?

In all documentaries, they say life developed in SHALLOW waters, so ruling out deep oceans...

Noclevername
2013-Dec-26, 08:41 AM
Out of curiosity, do we know for sure that life on earth developed on the land and not in water?

It's the ice layer that's problematic, it could keep the main sources of non-H2O chemicals from circulating in the ocean above.

ravens_cry
2013-Dec-27, 01:07 AM
That's not about the planet IMO, but the life that grows on it. It seems unlikely to me that even if we do find exolife, we'd ever encounter anything that biocompatible with Earth life. We may get some form of disease that can survive in us long enough to do harm, and some native life may be toxic to ingest, but measles and syphilis and things like smallpox, are viruses which are co-evolved parasites specifically adapted to certain hosts.
Given how life on Earth is directly or indirectly responsible for everything on Earth from the atmosphere to much of the geological make up of the planet, I'd say an Earth without Earth-like life is not Earth-like at all. That being said, I agree it's incredibly unlikely that said life should be similar enough for the above to be a danger, but not impossible as such.

Trakar
2013-Dec-27, 01:38 AM
In all documentaries, they say life developed in SHALLOW waters, so ruling out deep oceans...

This is inaccurate.

One of the leading theories of biogenesis is that it initially occurred near deep-water vents similar to black smokers (http://www.space.com/19439-origin-life-earth-hydrothermal-vents.html)