Talk:Planetary habitability

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September 2005 - January 2006

[edit] Anons concerns cont'd

On the grav-locked, red dwarf planet:

Note that a planet gravitationally locked to its star will have tidal heating like Io, so it's not as if everything will freeze on the night side. The great advantage of a grav-locked planet is its stability. I think it's fair to say that stability is easier for life to deal with than instability. If you look at the stability of Jupiter's great red spot (400 years and posited to be permanent), weather on a grav-locked planet should be relatively stable, I presume a convection rising at the "sun pole" and falling at the "dark pole", with terrain eddies, of course. Such a planet will have no axial tilt, no day/night cycle--I don't even think it can have an eccentric orbit, but I'm unsure. This greatly reduces the complexity of an organism's job: for example a plant doesn't need the night "mode" earth plants need; they would not have to drop leaves for winter. These seem like advantages to me.

Based on the best information I can find on the US Dept. of Energy site (solar information), what plants get on a clear equinox day is about 8 kWH/m^2, peaking at 1 kW/m^2. The vast majority of that power comes in the middle 8 hours, less than 1 kWH/m^2 is in morning and evening. The night is essentially 0 kWH/m^2--not absolutely, no, but to the 2 digit accuracy I was using, yes. (Compare visual magnitudes of sun vs. moon.) This varies by latitude and season, of course. Now let's plug this into the supposedly horrible 60-200% variation of a red dwarf. Instead of roughly 1/3 time at 1 kW (yes, it really is close to that), equivalent energy would be all the time at 1/3 kW. Thus, the variation would be 1/5 kW during minimums (=60% of 1/3 kW) and, of course, 200% is 2/3 kW. Thus, ignoring frequency, the red dwarf plant has an easier time. The lower power of red dwarfs just pull the HZ in. Considering Earth shade plants, which live on far less than 1 kW/m^2, the HZ is where the total solar and gravitational energy are right for water.

Organizationally, perhaps the best thing would be to treat Earth-like planets in the main flow of the article: then discuss tidally-locked red dwarf planets, with a note that thinking on the issue is in flux; and note that chemosynthsis biospheres would be possible even around brown dwarfs or outlying moons, like Titan and Europa. Perhaps (keeping original numbers):

1 Suitable star systems

• 1.1 Spectral class
• 3.1 Binary systems (since all but the closest binaries are ok, put it here)
• 1.2 A stable habitable zone

2 Planetary characteristics

• 2.1 Mass
• 1.3/2.2 Acceptable energy variation (as I hope I showed about, "low" isn't really necessary; include the case of Jovian moons in the HZ)
• 1.4 High metallicity (it comes from system formation but it's a planet property)
• 2.3 Geochemistry (maybe combine with metallicity?)

3 Alternative biologies

• 3.2 Red dwarf systems (tidally locked; low light?)
• NEW Chemosynthesis-based biology.

4 on, no changes.

I should add, this is a really good article. Maybe I'm trying to gild the lily.

[edit] Mistake ?

I am not a specialist but "Mars, by contrast, is nearly (or perhaps totally) geologically dead and has lost much of its atmosphere [10]." (mass paragraph) seems doubtful to me. I mean, Mars still has volcanoes (Mount Olympus for example) so it sees strange to me that it's geologically dead, but once again I am no specialist. Poppypetty 19:28, 1 February 2006 (UTC)

Mars does have volcanoes, but as far as I know, they're not really active, so nothing is really "powering them" and geological activity isn't really showing up. Mred64 22:49, 2 February 2006 (UTC)

Luna, Earth's Moon has volcanoes, and it's accepted as geologically dead. The presence of volcanoes doesn't mean ACTIVE volcanoes.CFLeon 21:59, 21 March 2006 (UTC)

That's basically what I was trying to say, I guess I just never made it really clear. Mred64 03:08, 27 March 2006 (UTC)

[edit] Picture Size

Can a larger size by found for the Habitability Zone picture? I'd like to use it as a background, but it won't scale up.CFLeon 21:59, 21 March 2006 (UTC)

I downloaded it here: http://library.thinkquest.org though I can't remember the exact spot on the site. An image search for habitable zone turns it up first thing, but only at 19k... Marskell 21:42, 24 March 2006 (UTC)

[edit] Earth's geological activity

I am pretty sure that the earth isn't geologically active simply because of its large mass/surface area ratio. From what I have read, I believe that planets are probably heated mostly by radioactive decay, and/or tidal forces, with heat from formation being significant only very early in their lives. See http://pda.physorg.com/lofi-news-heat-marone-mantle_62952904.html for example. It may be that the earth has an unusually large quantitity of radioactive materials. Clearly, the final temperature reached by a planet will be affected by the mass/surface area ratio, but I imagine that a mars-sized planet with a higher proportion of radioactives and/or large satalite could remain geoligically active. For that matter, if the moon orbitted significantly closer to the earth, the tidal forces on the earth would be immense (tidal forces are inversly proportional to the cube of distance?). --Pog 16:10, 25 April 2006 (UTC)

[edit] rate of binaries

The article says:

"Typical estimates often suggest that 50% or more of all stars are in a binary system. This may be partly sample bias, as massive and bright stars tend to be in binaries and these are most easily observed and catalogued; a more precise analysis has suggested that more common, fainter, stars are usually singular and that up to two thirds of all stellar systems are therefore solitary"

I fail to see the opposition. Consider 4 stars, two of them in a binary system, two single:

**       *        *

Here 50% of all stars are in a binary system. At the same time, two thirds of the stellar systems are solitary.

Should it, perhaps, read:

"that up to two thirds of all stars are therefore solitary"?

SHagel 12:17, 8 May 2006 (UTC)

[edit] Habitable to Whom?

This article seems to have a very narrow definition of life. Who is to say that an exotic form a life could not exist in conditions that would be considered extreme by human standards? The assertion that water is a pre-requisite for life is based on a single case study: our planet and our solar system. It may be that life exists elsewhere in forms we are currently unable to recognise. Would it not be more accurate to define planetary habitability as a planet whose conditions are favourable to human life, or earth-like life? --70.82.50.67 18:13, 15 June 2006 (UTC)

The problem is that we don't really know what life is. Are viruses alive? Or computer viruses? Prions? Is fire? We only have one sample of a process that we can comfortably call life, and it is the one we happen to be in. Therefore it makes sense, when searching for life out there in the cosmos, to stick to the one example of life we know of as our determining factor. Either that or come up with a workable definition of life which answers all of your objections, and I don't see that happening any time soon. Serendipodous 16:48, 16 June 2006 (UTC)

It is not asserted that water is necessary for life. It is strongly suggested, then qualified: "After an energy source, liquid water is considered the most important ingredient for life, considering how integral it is to all life-systems on Earth. This may reflect the bias of a water-dependent species, and if life is discovered in the absence of water (for example, in a liquid-ammonia solution), the notion of an HZ may have to be greatly expanded or else discarded altogether as too restricting."

The fundamental point is to follow the literature rather than introduce utterly speculative language or original resources. Numerous academics have defined habitability in terms of water—so then must we. Marskell 17:02, 16 June 2006 (UTC)

I am sure there are academic discussions out there on non-carbon base lifeforms or cycles that go without water nor oxygen. Even though the majority of search for life is based on water and carbon criteria, we need to mention other systems that have been explored or discussed. Here on Earth we've only recently discovered deep sea lifeforms like giant tube worms that thrives in inhospitable conditions to humans. There is no speculation that these are alive. Thus far, the article only mentioned discussions on possibility of other types of planetary system, nothing on alternative biochemistry cycles. --Kvasir 19:18, 25 April 2007 (UTC)

After a few search around wikipedia there should be enough material for a paragraph on alternative biochemistry in this article. Will add in a few hours. --Kvasir 19:36, 25 April 2007 (UTC)

The information in that section is ably covered by the alternative biochemistry article, to which this article already has a link (under geochemistry). Serendipodous 22:56, 26 April 2007 (UTC)

Yes, I'm not entirely sure it's needed. We already repeat ourselves enough 'round here. Marskell 22:58, 26 April 2007 (UTC)

A single sentence hidden there hardly suffice. Needed a paragraph at least to introduce the topic. Sentence is now better incoroprated into Alternative biochemistry paragraph. --Kvasir 00:47, 27 April 2007 (UTC)

Don't waste your time, This place is not run like a real encyclopedia where things make sense; this is a neo-fascist training ground. 205.200.236.34 (talk) 03:52, 4 May 2008 (UTC)

[edit] Reference markup

I just noticed that Marskell reverted by conversion of this article to cite.php markup. It's not so much that I feel this article must use cite.php, though that happens to be the system I consider best for almost all footnoting situations, but that I feel it shouldn't be using {{mn}}. This is the Wikipedia:Footnote4 system, a proposal that was never even adopted in the first place and which is now used by only about a dozen articles (see Special:Whatlinkshere/Template:Mn). Marskell, if you feel strongly that cite.php is inappropriate for this article, perhaps you could convert it to some other system that's currently in use? Wikipedia talk:Footnote4#Absorbed in Footnote3 suggests that the same functionality exists in the Footnote3 system, which is at least much more standardized across Wikipedia even if I don't personally consider it superior. Bryan 06:32, 18 June 2006 (UTC)

The main reason I reverted was because some work had gone into seperating the primary and secondary references and cite.php mashed them together. I will look at changing to a more common system. Thanks for the note. Marskell 09:47, 18 June 2006 (UTC)

I suspected that might be the case. I don't see much purpose in separating primary and secondary references like that myself, but there are plenty of other articles in need of reference work so I'm not going to worry about it. :) Bryan 05:12, 19 June 2006 (UTC)

[edit] Suggestion

Isn't Phosphorus a required element for life, even in its simplest form? DNA or RNA couldn't exist without their Phosphorus backbone. Quote from Wikipedia (topic "Phosphorus"): "Phosphorus is a key element in all known forms of life. Inorganic phosphorus in the form of the phosphate PO43- plays a major role in biological molecules such as DNA and RNA where it forms part of the structural backbone of these molecules." http://en.wikipedia.org/wiki/Phosphorus Hugo Dufort 04:55, 28 September 2006 (UTC)

In the strictest sense, all we can say for sure is that life requires an energy source. Any other point speaks to "life as we know it" but not necessarily "life as we don't." Even "life requires water" may be parochial. That said, a sentence on phosphorus could be worked in, if you can find a non-wiki source. Marskell 08:19, 28 September 2006 (UTC)

Of course, all life that we know contains genetic material, a necessity for self-replication, an assumed property of life. All known living things have RNA, a phosphate-containing substance (all animals have DNA, phosphate-containing substances); all use ADP and ATP (adenosine diphosphate and adenosine triphosphate) in the transfer of energy. It's hard to imagine any element that could substitute for phosphorus in either context. Vanadium? Arsenic? Those are both far rarer than phosphorus. One can rule out nitrates because they are excessively-strong oxidizers for most living things to imaginably use.

Sulfur is known to exist in some essential proteins. We could also contemplate four electrolytes that exist in blood (sodium, magnesium, potassium, and calcium). To be sure, sodium has no known function in plants. Add iron.

A terrestrial planet that has adequate carbon almost certainly has adequate nitrogen, oxygen, phosphorus, sulfur, iron, sodium, magnesium, potassium, and calcium.

It is safely said that any life that uses no phosphates is by definition exotic. Sulfur appears in some essential proteins. Life without sulfur is more imaginable than life without phosphorus -- but a planet with phosphorus almost certainly has sulfur as well. --Paul from Michigan 02:43, 30 April 2007 (UTC)

[edit] Cellular life

The article is focused solely on cellular life, as far as I can see. I think we should talk about how we can mention the possibility of other forms of life in this article. All discussion can go here.

Exactly, to definte life as only those that has cell structure (as we know it) is too narrow. See alternative biochemistry. --Kvasir 18:03, 26 April 2007 (UTC)

[edit] Red Dwarfs, Habitable Zone, and Tidal Locks

It's true that a planet in the standard HZ with a tidal lock would have problems with life because one side is so hot and the other is so cold. But what about a planet further than the HZ? The side always facing the dwarf would be cool enough to match earth temperatures! Sure, half the planet would be too cold to support life, but half a planet is better than none. DragonAtma 69.122.126.146 05:42, 8 December 2006 (UTC)

Would a planet that far away get enough stellar tide to be tide-locked? And would the problems of massive winds due to temperature differences, etc. still apply? Noclevername 21:29, 28 April 2007 (UTC)

[edit] Eccentricity

"This could very easily be the result of sample bias. Often planets are not observed directly, but rather are inferred based on the "wobble" they cause on their parent star—the greater the eccentricity the greater the perturbance in the star, and thus, the greater the detectability of the planet."

This contradicts some text in certain article elsewhere: Extrasolar_planet

"This is not an observational selection effect, since a planet can be detected about a star equally well regardless of the eccentricity of its orbit."

Fix it here or there. —The preceding unsigned comment was added by 83.144.95.66 (talk) 16:58, 10 December 2006 (UTC).

Fixed. The latter was the correct statement. Kevin Nelson 23:27, 13 February 2007 (UTC)

[edit] link

http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2286&mode=thread&order=0&thold=0

[edit] Inline citations

Per WP:MOS, inline citations go always straight after the punctuation mark and not before. I think all of them in the article should be fixed. —Anas ^talk? 17:05, 26 April 2007 (UTC)

The whole citation structure needs to be over-hauled. It's been on my to-do list for a year and should be done by, say, 2008. I created an enormous headache setting it up the way I did. Marskell 17:14, 26 April 2007 (UTC)

Hehe, yikes! Good luck with that. —Anas ^talk? 14:04, 28 April 2007 (UTC)

A range of theoretical habitable zones with stars of different mass (our solar system in middle). Near the top: Epsilon Reticuli (star), ε Reticuli b and its (hypothetical) satellites. ε Reticuli Ab is almost certainly a gas giant but rocky satellites may be potentially Earth-like. Near the bottom: Gliese 581 c, a potentially habitable Earth-like extrasolar planet.

[edit] Image in "A Stable Habitable Zone"

The image in this section appears to be in disagreement with other sources. It seems to indicate that Epsilon Reticuli b is centred within the habitable zone of its parent star. The habitable zone is centred at 2.2 AU [1] while the planet b has an average separation of 1.16 AU from the star. —The preceding unsigned comment was added by 81.101.143.89 (talk) 00:57, 1 May 2007 (UTC).

Why is Europe shown orbiting Jupiter?

Ya, I see that. Maybe because they're so far to the left? He he. Need to tell the pic creator about the typo. Marskell 19:38, 2 May 2007 (UTC)

Will someone edit the grammar in the second picture caption. It is poor english 97.81.67.232 00:47, 25 May 2007 (UTC)M.Davis

(on topic) The positioning of that Epsilon Reticuli b in the center of the habitable zone of its parent star in the chart image is highly misleading (See the planet's article for details there). Such a false image does not belong on this article and will be deleted.
GabrielVelasquez (talk) 10:33, 13 January 2008 (UTC)

[edit] very close => Tidal Lock => stationary sun?? What about otr spin-orbit resonances?

just 6.3 days). At those distances, the star's gravity would cause tidal lock. The daylight side of the planet would

but this is not quite true, isnt it the case that the planet might be locked the way Mercury is to Sun, making 3 rotations in 2 revolutions? And probably other such configurations. This is what the recent paper on Red Dwarf habitability mentiones as an option, but it doesnt mention what are the relative likelihoods of such configurations. Anyone know any info on this? Im hesitant to edit before getting some feedback on this. the paper in question - http://www.liebertonline.com/doi/pdf/10.1089/ast.2006.0124 (or perhaps the one above, in the same issue of Astrobiology i didnt doublecheck, i think its the link I give - but the whole edition is at http://www.liebertonline.com/toc/ast/7/1 ) --89.172.84.10 08:14, 31 May 2007 (UTC)

Also I wonder about that picture with a gas giant in a habitable zone of some big star as potentially habitable. In the article "a case for habitable exoplanet moons" http://www.physorg.com/news65376545.html it is mentioned how such moons would be habitable at twice the earths distance from the sun around a sun sized star, because of the compression heating by the gravitational forces of the giant, so wouldnt that mean that moons that are just in the habitable zone would possibly too hot, depending on the eccentricity of their orbits? In either case, it would be great if there was a list of discovered gas giants that could potentially have habitable moons. --89.172.84.10 08:23, 31 May 2007 (UTC)

[edit] Should we show different sizes?

I think it would be better to show both the size we currently show in the picture, and the larger possible size in a different colour. Zazaban 18:43, 14 June 2007 (UTC)

[edit] References

I just found and put up some really interesting info on red dwarf habitability but I can't get my head around this page's reference system. I'd appreciate it if someone with more knowledge could work it in. Thanks. Serendipodous 07:47, 18 June 2007 (UTC)

[edit] Tidally locked planets do not rotate?

"However, a tidally locked planet does not rotate, and so cannot produce a geodynamo at its core."

What does it mean, "does not rotate"? Tidally locked planets rotate, and their period of rotation is equal to orbital period. If planet didn't rotate, it couldn't possibly keep one face toward the star.

[edit] Microenvironments links

Cut for future use.

• University of Washington Astrobiology Seminar Series (2006-11-14).
• Deliquescence in the Atacama July 10, 2006
• Evolution distribution Origin of life universe - Life beyondJune 5, 2006
• Impact Craters as Biospheric Microenvironments, Lawn Hill Structure, Northern Australia June 5, 2006 Marskell 07:24, 6 August 2007 (UTC)

[edit] High mass limit

On the other hand, most scientists dismiss findings of large planets with a mass greater than that of Jupiter as "gas-giants" and therefore not habitable. I looked everywhere to find out why a planet with high mass would not be habitable and I can't find the answer -- not even here in wikipedia. So please, can we have an expert modify this section to explain the other end of the spectrum, why high mass planets cannot be habitable? Why do we assume that a planet with high mass be necessarily a "gas-giant" just because those in our solar system are that way? If we set that assumption aside for a minute, we would realize that we have already discovered dozens of planets that meet every other criteria for habitability. This does not necessarily mean that alien life already exists there, but that it could sustain us if we had the ability to get there.

Check out the stats for planet HD 28185 b, for example. Its distance from its star is 1.03 AU (Earth is 1.00 AU), its Orbital period is 383 (± 2) days (Earth is 365.25), and its Eccentricity 0.07 (± 0.04), even less than the Earth. Its star is G5 spectral type, again meeting the criteria. All of this would make it habitable, were it not for the fact that we already ruled it out because it is 5.7 times the mass of Jupiter. This planet's stats are found here, http://exoplanet.eu/planet.php?p1=HD+28185&p2=b and there are at least two dozen other planets with similar characteristics. So somebody, please explain, why does that automatically rule it out. Can't a large planet also be terrestrial? -- 23:14, 7 March 2008 User:Kyrkarena

[edit] Kangaroo court deletion of Planetary human habitability

For those of you who did not get a chance to vote on the importance of the Planetary human habitiability article
and who are not aware of the slimy facist deletion of this article, here its kangaroo court procedings:

http://en.wikipedia.org/wiki/Wikipedia:Articles_for_deletion/Planetary_human_habitability
http://en.wikipedia.org/w/index.php?title=Planetary_human_habitability&diff=199773394&oldid=199773315
(Note that redirect is the same as deletion since the article has been buried, also it was a complete lie that there was no referencing at all as most everything there was referenced!)
198.163.53.10 (talk) 16:03, 26 March 2008 (UTC)

Wikipedia isn't a democracy I'm afraid. Still, the article, from what I read, was basically a skimpier version of this one. I don't really see what that article had that this article didn't. Serendi^podous 16:08, 26 March 2008 (UTC)

No not a democracy buy facism is okay. There is nothing that is contained in the former article that is contained in the one it is redirected to, you didn't even read the comments in the kangaroo court or you would know that they are from different perspectives different values, you dare to pretend that you read it and read the article and you defend the proceding in ignorance. Where are the human tolerance limits?? where is the differenciation of super-bacteria habitiability and human habitiability. Are you aware that you are defending the idea the you have the same environmental tolerances as bacteria??
198.163.53.10 (talk) 17:02, 26 March 2008 (UTC)

I don't have to pretend, I did read it. It's right here. Axial tilt, eccentricity, hydrosphere and stellar class are all dealt with in the planetary habitability article, and in much more detail. Also, some of that article's claims, like that scientists believe that there is another human-level civilisation as close as 200 ly from Earth, were simply bizarre. There were no specific claims made in that article as regards humans. There was no mention of human tolerances, human stresses, human adaptations. Besides, what is the article for? If we find another habitable planet, we're not likely to inhabit it any time soon. Serendi^podous 17:58, 26 March 2008 (UTC)

Nothing in that article talks about other civilizations 200ly away, you lie to make something better than you can do look bad.
You refer to only four points in the other article, out of a total of fourteen issues/parameters that are brought up in the "Planetary human habitiability" article.
Again do you have the same constitution as bacteria?
("You lie! Captain Kirk was only doing his duty. - Chekov, ST2") 198.163.53.10 (talk) 19:08, 26 March 2008 (UTC)

I lie? How do you know? Lying implies a conscious attempt at deception, and unless you can read my mind you have no idea whether I believed my statement or not, even if it isn't true. As it happens, I was looking at an earlier version. Still, you say that humans are not like bacteria, but a) the planetary habitability article does not restrict itself to bacteria and b) your article does not specifically mention humans, except in the title. So I don't see what the issue is. Serendi^podous 19:21, 26 March 2008 (UTC)

• 198.163.53.10, since you have such strong opinions on the subject, perhaps you should create an account and log in. And discussion should be kept reasonably civil. --- Taroaldo (talk) 19:32, 26 March 2008 (UTC)

sure while these guys get away with lying to get something deleted... a bunch of criminals, what difference does it make. 198.163.53.10 (talk) 21:14, 7 June 2008 (UTC)

If it makes no difference, then why are you still here? Serendi^podous 13:00, 8 June 2008 (UTC)

[edit] Seven notes...

I find the existence of the seven "Notes" in the article disturbing. They are not citations, they are discussions and explanations. I realize that this is a complex topic, but Wikipedia's style is to tightly organize the information and these seven notes are ... not in keeping with the style of our other 1000 FA's. Perhaps I am looking for these notes to be at the end of each section, rather than at the end of the article. I will think about this some more before commenting further.--SallyForth123 18:32, 5 August 2007 (UTC)

You are right, it's self-sourcing and totally against the guidlines of the encyclopedia
198.163.53.10 (talk) 16:07, 26 March 2008 (UTC)

Notes are common in Wikipedia articles; they're used to illustrate information that is not immediately germane to the article itself. Many FAs have notes. I've written several myself. Serendi^podous 10:04, 8 June 2008 (UTC)

[edit] THIS ARTICLE SUCKS BECAUSE...

This article sucks because it does not take into account all the factors raised by Stehphe H Dole and Issac Assimov in their paper "HABITABLE PLANETS FOR MAN." 198.163.53.10 (talk) 21:18, 7 June 2008 (UTC)

Why are humans so important? What difference does it make if a planet is human habitable? We're just one life form out of millions on Earth, and we're not likely to reach another star system for millennia. Right now scientific interest lies in finding life on other planets, not in finding planets suitable for human life. Serendi^podous 10:00, 8 June 2008 (UTC)