MEarth-1b?

http://www.docstoc.com/docs/15604836/2-Science-Objectives-The-discovery-of-extra-solar-planets

Quote :

With the realization that rocky planets may well be plentiful around M-dwarf stars, a number of ground-based surveys have started regular monitoring of a significant number of these objects as e.g. the M-Earth Project (Irwin et al. 2008) with the expectation that around these small stars, super-Earth (or smaller) planets should be detectable. Given the low luminosity of the star, the habitable zones in these objects are close in, and it is likely that ground based surveys could well be able to detect planets in these regions within a few years. The faintness of typical M-dwarf host stars will make detailed characterization follow-up really challenging, even with the future giant telescopes or with JWST. Enthusiastically, a first discovery from the M-Earth project (still non public, to appear in Nature, in Dec 2009) is revealing a super-Earth with a mean density very different from the one of CoRoT-7b despite similar masses (Fig. 2.4).

Information from transits.
Transit observations have led to some remarkable results. We have found almost a factor of two variations in the size of giant planets of similar masses (with unexplained cause) and begun to study their internal structure through comparison of their bulk density with theoretical models. Although still based on small statistics, the situation seems to be similar for super-Earths, for which the CoRoT and M-Earth candidates present fairly different radii (1.7 and 2.7 Earth radius) despite estimates of their masses that are not very different (4.8 and 5.7 Earth masses, respectively). This demonstrates once more the variety of possible outcome from planet formation processes. Recently, we also have started to gather hints about the orbital dynamical histories of transiting planets through the Rossiter-McLaughlin and Kozai effects. Very surprisingly, it turns out that about 1/3 of the known transiting planets are misaligned (not crossing the stellar disk perpendicularly of the star rotation axis; Collier-Cameron, Porto conf. 2009), a strong indication of stockastic processes during the planet formation or evolution.

If this breach embargo, delete post.

I was successful in accessing the paper without the use of "guess the URL" or other such tactics. This document is on a document host site where every document is freely accessible. As such, I authorized him to post this. I'll take responsibility for any unethical conduct here.

first "oceanides"-type planet?

Very interesting.

Have you got the orbital characteristics?

Is this planet habitable?

Stalker wrote:

Have you got the orbital characteristics?

Is this planet habitable?

In article about them nothing no. But probably in the near future (in December) published article in Nature.

Judging by the anomalously high radius, the planet may be a sub-Neptune, rather than a terrestrial, as has been suggested for the planets at HD 40307.

http://www.astro.ex.ac.uk/esp09/presentations/Berta_Monday.pdf
on tenth page in presentations MEarth group from September 2009 is spoken about three good transit candidats with period at 0.2, 3 and 3 days.

5,7MT/(2,7RT²)=0,78 g for the gravity on the floor of this planet

0.78 G looks very odd for a planet with 5.7 Earth masses and 2.7 earth radius.

Not likely to be a rocky world.

Density is 0.28 Earth density, 1.4 gm/cm3. Lower than Neptune by quite a bit.

Discovery paper is up at Nature, behind paywall. Tables and figures can be freely accessed however.

Extrasolar Planets Encyclopaedia page

The planet is called GJ 1214 b or/and MEarth-1b?

The abstract of the discovery paper calls it GJ 1214b, I guess MEarth-1b was a temporary designation used while the host star remained unidentified.

The planet could be a "hot Super-Pluto".

AS we all know, Pluto is a world composed of 50% rock and 50% ice. The newly discovered planet would be a much larger version of Pluto in terms of composition. The planet could have formed well beyond the snow line, so a significant portion of the planet's mass is ice. If the planet underwent inward migration to where it is now, then the top icy layer would melt, then as the planet got even closer, the planet would build up an atmosphere of hot steam. Around a Sun-like star, the water molecules would be photolyzed by ultraviolet radiation. The host star, however, is not sufficiently hot to emit much ultraviolet radiation, so the steam just simply builds up over time. As it stands now, the planet receives 170 times the stellar insolation that Earth does, which would make the planet very hot. Having over five times the mass of Earth, the planet would be able to hold onto an atmosphere of hot steam almost indefinitely.

The diameter of the planet as measured from the transit is 34500 km (21400 miles). If the planet's compositon is similar to Pluto (which very well could be the case), the uncompressed density would be around 1.7 g/cm^3. Accounting for gravitational compression, the actual diameter of the planet itself could be around 30000 km (18600 miles). The difference between the two values would be due to the atmosphere, in this case, an atmosphere of super-heated steam that is around 2200 km (1400 miles) thick. Given that water vapor is a greenhouse gas, the planet's surface would be extremely hot. Not exactly a friendly place for life.

AVBursch wrote:

an atmosphere of super-heated steam that is around 2200 km (1400 miles) thick.

Wow. What would the pressure/tempreture be at a sea level, such as it is and can water stay liquid?

Hmm! These guys say the Thick Atmosphere is H2/He though. In any case we should know soon.

A super-Earth transiting a nearby low-mass star
http://arxiv.org/abs/0912.3229

Abstract wrote:

A decade ago, the detection of the first transiting extrasolar planet provided a direct constraint on its composition and opened the door to spectroscopic investigations of extrasolar planetary atmospheres. As such characterization studies are feasible only for transiting systems that are both nearby and for which the planet-to-star radius ratio is relatively large, nearby small stars have been surveyed intensively. Doppler studies and microlensing have uncovered a population of planets with minimum masses of 1.9-10 times the Earth's mass (M_Earth), called super-Earths. The first constraint on the bulk composition of this novel class of planets was afforded by CoRoT-7b, but the distance and size of its star preclude atmospheric studies in the foreseeable future. Here we report observations of the transiting planet GJ 1214b, which has a mass of 6.55 M_Earth and a radius 2.68 times Earth's radius (R_Earth), indicating that it is intermediate in stature between Earth and the ice giants of the Solar System. We find that the planetary mass and radius are consistent with a composition of primarily water enshrouded by a hydrogen-helium envelope that is only 0.05% of the mass of the planet. The atmosphere is probably escaping hydrodynamically, indicating that it has undergone significant evolution during its history. As the star is small and only 13 parsecs away, the planetary atmosphere is amenable to study with current observatories.

TheoA wrote:

... such as it is and can water stay liquid?

According to this paper, apparently not.

Three Possible Origins for the Gas Layer on GJ 1214b
http://arxiv.org/abs/0912.3243

Abstract wrote:

We present an analysis of the interior composition of the new MEarth transiting super Earth exoplanet GJ 1214b. The relatively low average planet density (\rho_p=1870\pm400 kg m^{-3}) means that GJ 1214b almost certainly has a significant gas component. Based on the mass and radius alone, (M_p=6.55\pm0.98 M_{earth}, R_p=2.678\pm0.13 R_{earth}) we cannot infer a unique composition of the interior or the gas layer. In this paper we explore the range of possible origins and compositions for the gas layer by considering three end-member scenarios that account for the observed mass and radius: a mini Neptune, a water planet, or an outgassed super Earth. If GJ 1214b is a mini Neptune or outgassed super Earth, a hydrogen-rich envelope accounting for ~< 1% of the planet mass could account for the planet radius (in contrast to Neptune's 5-15%). Alternatively, the measured mass and radius are also consistent with a water planet scenario in which GJ 1214b is composed of at least 47% H2O by mass and is surrounded by a massive steam atmosphere. We find that in this scenario, given our water EOS and reasonable assumptions for the planet albedo and interior luminosity, GJ 1214b would be a so-called hot-ocean planet with an outer steam atmosphere that transitions continuously to a superfluid without passing through the liquid phase. Regardless of the true nature of GJ 1214b, the relatively low density means it is certainly a new kind of planet with no solar system analogs.

(emphasis mine)

What mean "D" in the spectral type of the star (M4.5 D (simbad))?

Holy Cow.

Now that's a new planet type.

Super Critical Steam Planet.

On a side note Super Critical Steam is one of the most effective sterilizing agents
for organic compounds there is. Even dioxins are not stable in it.

http://oklo.org/2009/12/16/mearth/
Greg has his money on these being a new class of water planets, including Corot-7B.

The paper said "superfluid", not "supercritical"

http://en.wikipedia.org/wiki/File:Phase-diag2.svg

Hmm! according to this chart water only has a Super Critical Fluid phase above the critical point.

There is no Super Fluid phase as in H2/He.

Or am I missing something.

I also found this strange, especially as superfluids exists only in low
temperature. Always this is what he wrote in the paper. Can be an error?

I think this is an error in the paper, they wrote "superfluid" instead of "supercritical fluid" - the two are very distinct concepts. Supercritical fluids are fluids above the critical point, superfluids are a far weirder state of matter.

Stalker wrote:

What mean "D" in the spectral type of the star (M4.5 D (simbad))?

If you hover your cursor over the "Spectral Type" text, it describes it as an accuracy tag.
A -> Good quality measurement. D -> low quality measurement. This comes from difficulty in reading the spectral lines due to either the star being faint, or its spectrum contaminated. It is not a property of the star itself, rather, the quality of the measurement.