New habitable zone estimates

Habitable Zones Around Main-Sequence Stars: New Estimates
http://arxiv.org/abs/1301.6674

In particular the cloud-free inner boundary of the HZ is moved outward as compared to the Kasting et al. (1993) estimates. The onset of "moist greenhouse" conditions is predicted at 0.99 AU (versus 0.95 AU) and the runaway greenhouse at 0.97 AU (as opposed to 0.84 AU). However:

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Although it appears that Earth is perilously close to the inner HZ edge, in reality, cloud feedback and low upper tropospheric relative humidity act to stabilize Earths climate.

For stellar temperatures below 5000 K, the distinction between the two inner boundaries disappears.

According to figure 8, Earth, HD 40307g, Gl 581d and Gl 581g are in the HZ for cloud-free planets. Kepler-22b, Gl 667 Cc, and Tau Ceti e and f are not. As for the case of clouds:

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Our model does not include the radiative effects of clouds; thus, the actual HZ boundaries may extend further in both directions than the estimates just given.

I am sceptic about any estimates of hz of any star.In case of our solar system hz can be wide enough to contain 3 planets.90 bars pressure of Venusian atmosphere can not be any proof in which life can not have comfortable condition to develop at 0.7-0.8 AU if day would be normal(not243 days) and composition of air would be different.Example of Venus and mars are freak.On the other side mars has very thin atmosphere 10 times more pressure and would change all.The cases of Venus and mars will not happen in any other planetary systems as there could be more nitrogen ,oxygen and water

They give themselves an out, I noticed. At the end of the opening comments, they state that their model didn't include the effects of clouds, thus extending the HZ further in both directions.

So, to quote Monty Python, "It's only a model."

-M-

Solve the clouds problem and you've made significant progress in climate modelling...

Planetary Habitability Laboratory: let's have a press release!

Scientists redefine 'habitable zone;' Earth booted out of 'Goldilocks zone'

Guess it makes for some hyperbolic headlines...

Sirius_Alpha wrote:

Scientists redefine 'habitable zone;' Earth booted out of 'Goldilocks zone'

Guess it makes for some hyperbolic headlines...

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Funny ,very funny only prooves all the estimates are piece of kittens and else not existing gliese 581 g

-- Edited by Sirius_Alpha

Well given the increase in solar luminosity over the last 4.5 billion years or so it maybe shouldn't be too surprising that the Earth is close to the inner edge of the HZ. No particular reason we should be in the optimum part of the HZ (and I really have to wonder what life would be like on the presumably more CO₂-rich worlds further out in the HZ, I'd guess for starters that ocean acidity might have an effect on the evolution of things like shells).

Of course if you end up showing Earth is not a habitable planet you've really demonstrated that there's a flaw in your model (which the authors of the paper themselves specifically take pains to point out, i.e. the lack of cloud modelling). Nevertheless, even without the clouds Earth does end up being just inside the habitable zone despite what hyperbolic headline writers are saying...

They(scientists)mostly if not all assess low albedo considering habitability up to 0.3.Planets with radii between 1.3-3.0 surely are water worlds with much thicker clouds content and some even ice planets they have higher albedo even as high as saturns moons

Point taken about the clouds, but ice planets wouldn't be habitable though, so there's not much of a great need to consider albedos that high.

You could also in principle get a higher albedo from Rayleigh scattering in a sufficiently thick atmosphere. E.g. this paper (pdf) gives a cloud-free albedo for 0.4 (higher than the Earth's albedo) mainly as a result of Rayleigh scattering.

Like Lazarus wrote this is the case I guess most planets if not all within range 1.3-3.0 earth radius have surely much thicker atmosphere than earth especially in hz where is no mass loss zone due all stellar irradiation.So seems to be that planets with radii over 1.5 have higher albedo and under 1.2 lower.I think earth has thin atmosphere and most planet with even similar radius can have higher albedo

A question what albedo has ultralight minineptune kepler11 f for example?

HD 85512 b and Tau Ceti f have been crossed out of the PHL list.

Amusingly HD 85512 b has a higher ESI value than some of the planets that remain in the list, which I suppose goes to show how useful the ESI is as a means of estimating habitability.

How close is Earth to a runaway greenhouse?
http://arxiv.org/abs/1306.5730

Adding relative humidity parametrisation moves the inner boundary (as defined by the moist greenhouse effect) to 0.97 AU. The calculations are still probably overly pessimistic due to omission of cloud feedback and the possibility that relative humidity may increase more slowly with temperature than assumed.