Now that you mention it i recall i have heard that aswell, but extremely small ones newertheless. Mercury gets it blown off all the time due to solar wind, but i guess that the extreme temperatures on Mercury allows it to have some very heavy gasses that the solar wind can't blow away from Mercury's gravity. On the other hand Pluto has got to have very light gasses, but they can hang on to the planet because of the low solar wind.

And this leads to something i have considered after i read something that caught my interest. Astronomers suspect Enceladus to have had an atmosphere, which has now vanished. What happened with this atmosphere? I guess it can't be the solar wind, which isn't such a big factor at Enceladus.

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"The world is a fine place and worth fighting for." (Ernest Hemmingway)

I think it will be quite a while before humans discover an Earth-sized planet that we can say for sure has oceans of liquid water and/or a breathable atmosphere. Given the disappointing delays (due primarily to space science budget cuts) such a planet, if it exists, probably will not turn up until sometime after 2020.

Having said that, I think we will find scads of terrestrial planets (some even as small as Mercury and Mars) between 2010-2015. As the Kepler mission website points out:

URL: http://kepler.nasa.gov/sci/basis/sizes.html
"Note that although the mission is optimized to detect Earth-sized planets in the habitable zones of solar type stars, planets even sas small as Mercury will be detectable in the habitable zone of K and M stars."

I think, although I am still somewhat skeptical of some of their numbers, that the microlensing technique will reveal the first Earth-mass planet around an M dwarf some time between now and 2012.

Don't count out the RV technique. Has anyone else heard of the Rocky Planet Finder telescope which still needs funds but is right now being constructed in California? If Marcy et al can get the remaining funds, then the RPF telescope may be starting its 365 day a year search for planets of 1-20 Earth masses out to 0.5 AU around stars slightly less massive than the Sun.

So, it's basically a three way race between the Rocky Planet Finder telescope, microlensing searches, and satellite photometry searches as to what group will find the first Earth-mass planet.

Which group/technique do you all think will bag the first extrasolar Earth?

I think Kepler will. Is it a spaceborn or ground-based telescope you are talking about?

Well, as said, please check the criterias again i wrote at the beginning of this thread. I know it is my own fault people are missing my point, but breatheable atmosphere was not a criteria. I will just slightly rewrite the criterias, but it should be the same, just easier to understand than what i first read

Criterias
- Size: +/- 50% of Earth.
- Mass: +/- 50% of Earth.
- Distance: In the habitable zone.

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"The world is a fine place and worth fighting for." (Ernest Hemmingway)

It is liquid due to pressure. I don't think that, just because the Earth's core is molten rock, it should not still be considered a 'rocky planet'.


In fact, I think that rocky versus gaseous designations have much less to do with matter state than they have to do with composition. Earth is nickel and iron and oxygen - intrinsically rocky, metallic material regardless of state, whereas Jupiter is mostly hydrogen and helium.

Again, hard to say since we haven't got a definition of it yet. Jupiter, Saturn, Uranus and Neptune are quite easy to designate as gas planets as they are so different than Mercury, Venus, Earth and Mars.

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I'm proposing it as a definition.

Yes, but what about the other planets that we are finding outside the solar system? I would propose to say that 50% of the planets volume has to be gas in order to be considered a gas planet.

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a] I propose that its designation has more to do with its composition (such as the elements) than with its more dynamic properties (such as its ratio of solid/gaseous).

b] But if it were biased toward state (solid/gas) as per your definition, then I porpose that a planet with significant rocky volume should only be gaseous if that volume is small i.e. 75% gas / 25% solid is still rocky IMO.

Nevertheless hard to tell what the scientists will define it once they decide to make such a definition. I wouldn't be surprices if it was a more complex thing than just 50% or 75% of the volume or mass. Yes, maybe something that has to do with its composition.

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Thank you for the link. The modelling of the solar system he talks about should go Boinc. In that way we could get pretty nice prediction about the solar system and get more knowledge about the evolution of the solar system in case we change some parameters like Jupiter's position and size as he mentions in the interview. I would love to run this project on my Boinc manager.

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http://www.esa.int/esaSC/SEMZ4E1A6BD_index_0.html
I wonder though if this is realistic or "promotion" by the scientists in charge of the project.

Wow, amazing. Never read that about GAIA. I guess they to write a realistic estimate. If they didn't do it, they would have some nasty arguing afterwards.

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"...Gaia's measurements will be so accurate that, if it were on Earth, it could measure the thumbnails of a person on the Moon. ..."

Think that will finally shut the Moon Hoaxers up?

Nope. We could drag a Moon Hoaxer to the Apollo 11 landing site, slam their forehead into the dedication plaque until you could read it clearly, roll their head in ink and make a rubbing from it, and you'd still have people claiming it was fake.

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I'm not completely heartless, the doctor who removed it told me he'd never be able to get it all.

If GAIA finds numerous planets a little larger than the Earth, we will have to try to imagine a whole new class of worlds. Uranus is the next step up in mass in our solar system, at fourteen Earth masses. The properties of planets with between one and fourteen Earth masses are likely to be quite different to anything we are familiar with. I would anticipate planets with a solid core and thick atmospheres, half way between terrestrial and gaseous.

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There's already a couple members of that family. One was the five Me iceball that we got through lensing, the other is a 13 mass rock that was found by radial velocity. I think there are a couple others.

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I'm not completely heartless, the doctor who removed it told me he'd never be able to get it all.

I was thinking particularly about this world;
http://en.wikipedia.org/wiki/Gliese_876_d

Hot, probably dense, probably with a thick atmosphere; other similar planets should be found further out from their local star, cooler, no doubt, and with a wide range of conditions in their atmospheres. What a zoo there must be up there to discover...

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