Talk:Habitable zone

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[edit] Diagram wrong?

I believe that the y-axis on the digram of habitable zones associated with this article is actually showing the luminosity of stars relative to the Sun, not their masses. A main-sequence star with twice the Sun's mass has a luminosity approximately 10000 times that of the Sun, so its habitable zone would be centered at sqrt(10000)*(1AU) = 100 AU, not 1.5 AU as the diagram suggests. Conversely a star with twice the Sun's luminosity would have a habitable zone centered at about sqrt(2)*(1 AU) = 1.4 AU, as the diagram shows, if we interpret the y axis as luminosity, not mass. Am I missing something? —Preceding unsigned comment added by 130.113.174.152 (talk) 16:36, 28 February 2008 (UTC)


[edit] Need to State Earth's Current and Long Term Habitable Zone

Earth's current habitable zone (HZ) is 0.95 astronomical units (AU) to 1.37 AU. Earth's long term HZ is 0.95 to 1.15 AU.

Also suggest adding NASA graphic of earth's HZ: [1] Joema 14:36, 22 December 2005 (UTC)

Yes, I think merging Circumstellar Habitable Zones with Habitable Zones would be a good idea. Good idea to add current terrestrial habitable zone limits too. The NASA graphic already shows current CHZ based on the criteria discussed in the new addition. -- Dr. L.R. Doyle

[edit] Habitable to Whom?

"In astronomy a habitable zone (HZ) is a region of space where conditions are favorable for the creation of life."

Does this not depend on your definition of life? Who is to say that other forms of life could not exist in conditions that humans would consider extreme? Wouldn't it be more accurate to say that the habitable zone is a region of space where conditions are favorable for the creation of human life, or earth-like life? --70.82.50.67 18:03, 15 June 2006 (UTC)

"and iodine for the the thyroid gland" Do extra-terrestrial organisms have thyroid glands? Can someone cite this?

Absolutely. We already know there is life existing on areas of Earth which would earlier have been be considered outside the habitable zone for "life as we know it". In Evolving the Alien: The Science of Extraterrestrial Life, Ian Stewart and Jack Cohen make a convincing case that "Goldilocks zone" represents a dearth of imagination. Earth seems amazingly well suited to us because it's where we evolved. Daibhid C 23:21, 24 October 2006 (UTC)

[edit] galactic Habitable Zone?

I was looking at an article on the milky way and clicked a link for "Galactic Habitable Zone" that lead me here. However, there is less than 2 sentences total on it. Can an expert add some content please?RSido 17:46, 25 February 2007 (UTC)

[edit] Criticism or Opinion?

"However, while it is relatively certain that life on Earth would be able to adapt to an environment like Europa's, it's far less likely for life to have developed there in the first place, or for it to somehow move there and adapt afterwards without advanced technology..."

This seems awfully editorial in nature. Either that or it's in need of a citation.

Macmanui 22:19, 26 April 2007 (UTC)

Agreed. That sentece stuck out to me. Earth life would pretty much die instantaneously if those conditions were present on Earth. Jiminezwaldorf 09:34, 7 August 2007 (UTC)

[edit] HZ around M dwarfs

I don't know how widely this is accepted, but I noticed this sentence in the abstract of this paper:

http://arxiv.org/abs/astro-ph/0609799 Title: A Re-appraisal of the Habitability of Planets Around M Dwarf Stars

Observations of protoplanetary disks suggest that planet-building materials are common around M dwarfs, but N-body simulations differ in their estimations of the likelihood of potentially-habitable, wet planets residing within their habitable zones, which are only ~ 1/5 to 1/50 of the width of that for a G star.

I mention it to compare to the graphic in the HZ article. —The preceding unsigned comment was added by 66.113.30.2 (talk) 02:47, 27 April 2007 (UTC).

[edit] No mention of width

It's not just one number, it's a habitable ZONE. So what determines the width of a HZ? The above comment discusses M stars only having a width of 1/5 to 1/50th. Can anyone help me?

210.23.136.200 02:04, 8 October 2007 (UTC) Tim

[edit] Criticism

"However, while it is relatively certain that life on Earth would be able to adapt to an environment like Europa's, IT'S FAR LESS LIKELY for life to have developed there in the first place"

Why is it so far less likely? Can someone show me just one proof?

The guy in the above line makes a good point. We have not yet seen life develop anywhere but earth, and so should be slow to rule out possibilities without evidence.

"A planet that used to be in the habitable zone is more likely to have life than one that has moved into it."

And again - why so?

132.177.70.205 16:17, 29 April 2007 (UTC)Ramond

[edit] Galactic habitable zone: Huh?

"Heavier elements must be present, since they form complex molecules of life, such as iron as the foundation for hemoglobin and iodine for the thyroid gland."

What do hemoglobin and thyroid glands have to do with the basic requirements for life? Carbon, Hydrogen, Nitrogen, Phosphorous and maybe a couple of others you can probably make a strong case for, but archaea do fine without hemoglobin. The plant world does fine with magnesium-based chlorophyll. Heavier elements are needed to form rocky planets, but not, as far as I can tell, for life itself. Life is opportunistic. If incorporating heavy elements that happen to be available makes things work better, it's liable to happen, but we're interested here in requirements common to all life as we know it.
I agree, the reference to thyroid glands is out of place in this article. Perhaps that sentence could be rewritten to retain a reference to the importance of metals to life; I don't know enough about biology to do it properly, but I'll probably try to clean it up a bit if no one better qualified does it in a reasonable amount of time. Deerslayer (talk) 21:27, 2 March 2008 (UTC)

"On the other hand, the solar system must be far enough from the galaxy center to avoid hazards such as impacts from comets and asteroids ..."

This is the real "Huh??". Is the suggestion that a passing interstellar asteroid from the galactic core is likely to hit a solar system? What would that mean? Asteroids and comets come from within a solar system. Comet impacts played an important role in providing water to the early earth. Asteroid impacts are not necessarily a hazard either. I've seen it claimed that they have played a vital role in evolution. Perhaps the idea is that a planet in a system nearer the core would be subject to too many asteroid and comet impacts, but if so, that should be spelled out. -Dmh 16:07, 10 May 2007 (UTC)
If I recall correctly, the argument is that a greater number of nearby stars will increase the chance of a comet's orbit changing from a star's oort cloud to a more elliptical one. I'll see if I can't find a source for that. Ƶ§œš¹ [aɪm ˈfɻɛ̃ⁿdˡi] 23:23, 6 September 2007 (UTC)
The idea is that the higher metallicity near the galactic core results in the formation of more and larger asteroids and comets. I believe that the concern regarding the danger to life is valid - think of the devastating effect of the asteroid that struck Earth 65 million years ago. Deerslayer (talk) 20:26, 2 March 2008 (UTC)

[edit] Removed editorial comment

Someone inserted the following comment into the page:

<<the previous statement is imprecise. please edit this contribution: it would be better to describe a star as "developing".
To begin with, it is heated by gravitational energy as its gas cloud contracts. It ignites certain nuclear fusion reactions between protons (hydrogen nuclei) and the nuclei of the next heavier elements, lithium, beryllium, and so on. This "getting hotter" period doesn't take any very large part of the life of a medium-sized star. For most of its life, the star then stays pretty steady in its output, burning hydrogen into helium. When enough of the hydrogen is used up, the star shrinks, and then gets hot enough to become violent. Possible end-products are a white dwarf, a red giant, a neutron star, or a Black Hole, AJR>>

Most of this is superfluous information about stellar evolution, so I removed it. I rejected the suggestion to describe the star as 'developing', because the term 'evolve' is well-understood and accepted in this context. I did remove the part from the earlier version about the star 'getting hotter', because there are obvious counterexamples (eg, evolution into a red giant), and because it's irrelevant to the point here - the position of the CHZ doesn't depend on how hot the star is, only on its luminosity. --130.155.198.32 (talk) 04:21, 14 January 2008 (UTC)

[edit] 'likeliest candidates to be habitable and thus capable of bearing extraterrestrial life similar to our own'

Whoever put this line in makes it look like were assuming a lot. 'similar to our own'Protoform (talk) 08:37, 13 April 2008 (UTC)