Scientific Forums


 

Add reply · Start new topic · Start new poll


> Exoplanets And Super Earths, Habitability limitations
Quantum_Conundrum
Posted: Jan 8 2011, 09:44 PM


Advanced Member
*****

Group: Power Member
Posts: 1943
Joined: 30-April 07

Positive Feedback: 30.43%
Feedback Score: -123


This thread is in response to yet another discussion on the news site, in which people ignorantly seem to think human beings would be able to surve on a terrestrial planet with surface gravity of as much as 4g.

I expressed arguments that I do not believe it would be possible for humans to live on a planet with 2g, and doubt it would be possible above about 1.5g. I used some basic assumptions about conditions, such as the assumption of density and composition of the planet being similar to earth, and a range of atmospheric conditions.

Weight

For the sake of simplicity in this section, let's just pretend we have exactly 1 atmosphere of pressure, regardless of planetary mass or gravity, etc. We just assume the atmosphere is somehow workable with little or no pressure suits or oxygen.

Yes, people such as pilots and astronauts can survive temporary g forces, but we must remember they are in a cushioned seat and it is only temporary.

Let's take an average person and compute what their weight would be on a planet of different gravity benchmarks, such as in terms of earth masses with average density same as the earth. Our average person will be 185lbs man at 1g. (mass of 83.33kg is same regardless of gravity).

Planet Mass_ Surface Gravity(g)_Weight(lbs)

1e 1.000g 185lbs.
2e 1.259g 233lbs.
4e 1.587g 294lbs.
8e 2.000g 370lbs.
27e 3.00g 555lbs.
64e 4.00g 740lbs.

So those are what your gravitational acceleration and body weights would be on terrestrial planets of same average density as the earth, but given these masses.

So if anyone wants to argue with these figures, they are derived from the formula for the volume and surface of a sphere, combined with Newton's Law of Gravity.

Now there are of course many, many ways to forma terrestrial planet, and it could have anything from a density approaching that of lead, to a density less than the moon, but for the moment we are only considering planets of similar composition to earth. That is, after all why we are interested in exoplanets.

There is a reason why somethng very large, such as an elephant, hippo, or rhino has such thick, dense bones, and such a large muscle structure, and of course walks on 4 feet. It's because the weight cannot be distributed for long duration on just two feet, or small bones.


Now I don't know about those reading this, but I can be honest about my physical condition. I just weighed on a scale to get it right. I am up to 210lbs, and not very active physically. I used to be active a long time ago, but the last several years not much at all. If I were on a 2g planet, I'd weigh 420lbs, and I know I'd be disabled, if living at all.

By the time you factor everything else related to gravity, it seems absurd for anyone to claim that humans could live, work, grow, and reproduce in a 2g environment on a permanent basis.

I haven't even considered other things yet that we can't exactly test, such as how super gravity effects the coefficient of friction, because we've never landed anything on a terrestrial object with more than 1g in order to test these effects. I do know from lunar landing videos that low gravity seems to correlate to lower coefficient of friction,because they kept slipping and falling in the stuff, though that was a dusty surface, so again hard to draw 1 to 1 relationships, BUT if you extrapolate you might expect that the coefficient of friction is also going UP as gravity goes up, within certain limits...

The only thing we've ever landed on any object above 1g was the gallileo probe, and it burned up right away in Jupiter's atmosphere. Ironically, the "surface gravity" for Jupiter at the top of it's clouds is ONLY 2.58g, which is nowhere near the 4g this ***** on the news site was talking about. So at 2.58g, the gallileo probe incinerated whilst under about the top 60km worth of atmosphere. Yes, it's hard to draw a comparison because Jupiter's atmosphere is so dense, but again, it's the only greater-than-earth gravity object we've "landed" on.

Exo-skeletons aren't as useful as you might first think. The exo-skeleton doesn't help reduce your own weight, even if you were inside something like the yellow loader from the "Aliens" movie, you'd still feel your entire weight. Assuming you're on a planet where you are light enough to not be smashed by your own weight, the exo-skeleton would help you lift objects. It can never solve the "gee, I'd weigh 420lbs at 2g, or I'd weigh 630lbs at 3g...I'm so screwed..." problem.


Pressure

This isn't necessarily as big a problem as gravity itself, as humans can dive below water on earth and survive in fairly high pressures with or without suits or submersibles. However, there are still significant limitations to ecology on a planet where the vaporization point and freezsing points of water is much different. Having double earth pressure would probably be safer than having half earth pressure. As I understand it, most people must wear an oxygen tank to finish a climb of Everest.

As I pointed out there, at 2 earth atmospheres, water vaporizes at 120C, not 100C. I have yet to find a phase diagram or chart that even goes beyond 2 atmospheres, so I don't know what the deal would be there. My argument was that it would likely be very difficult for convection to occur since the water would need far, far more energy to vaporize and then even more energy to rise against the gravity.
Top
flyingbuttressman
Posted: Jan 8 2011, 10:07 PM


noblesse oblige / nullius in verba
*****

Group: Power Member
Posts: 5869
Joined: 8-June 09

Positive Feedback: 68.66%
Feedback Score: 166


Isn't the capacity for critical thought an amazing thing?

Good post.
Top
Montec
Posted: Jan 9 2011, 06:24 PM


Advanced Member
*****

Group: Power Member
Posts: 921
Joined: 9-November 05

Positive Feedback: 61.29%
Feedback Score: 19


Hello Quantum_Conundrum
Don't forget that under equal energy input a higher pressure atmosphere will have a higher ambient temperature than a lower pressure atmosphere. To much atmospheric pressure will result in temperatures that will cook carbonaceous lifeforms.

smile.gif


--------------------
Competition is the essence of evolution.
Top
Quantum_Conundrum
Posted: Jan 25 2011, 07:07 PM


Advanced Member
*****

Group: Power Member
Posts: 1943
Joined: 30-April 07

Positive Feedback: 30.43%
Feedback Score: -123


QUOTE (Montec @ Jan 9 2011, 01:24 PM)
Hello Quantum_Conundrum
Don't forget that under equal energy input a higher pressure atmosphere will have a higher ambient temperature than a lower pressure atmosphere. To much atmospheric pressure will result in temperatures that will cook carbonaceous lifeforms.

smile.gif

Well, given the larger cross sectional area and thicker atmosphere, the "habitable zone" would be shifted a few percents farther away from it's host star as compared to a planet of the exact same mass as earth.

Well, it depends on the exact mass and composition of the atmosphere, and the mass and density of the planet to determine what the equilibrium surface temperature would be, but in general, the thicker the atmosphere OR the more massive the planet, the greater the temperature would be at the surface given the same solar inputs. A thicker atmosphere increases the cross-sectional area being struck by sunlight, which depending on atmospheric content, could increase net thermal input.

Depending on how fast it rotates, such a planet might have a truly gigantic magnetic field, as it's metalic core may be as large or larger than the entire mass of the earth.

In terms of technological possibilities, I think the ideal planet might be one with slightly lower total gravity than earth, but a thicker atmosphere.

For example, if you had 0.9g and double the atmosphere, this would greatly increase the bouyant force and other lift principles in aircraft, potentially allowing ultra-cheap, ultra-fast and efficient aire travel around such a world.
Top
Guest
Posted: Jan 25 2011, 07:28 PM


Unregistered









Doyle's "Habitable Planets for Men" comes to mind, as well as Zelazny's "Shadowjack".. cool.gif
Top
Capracus
Posted: Feb 14 2011, 07:03 PM


Advanced Member
*****

Group: Power Member
Posts: 5375
Joined: 5-October 06

Positive Feedback: 75.56%
Feedback Score: 41


Not exactly an exoplanet, but it may have been at one time
QUOTE
Largest planet in the solar system could be about to be  discovered.

Would Tyche be the 9th planet of our Solar System, after Pluto's demise? If its existence is finally confirmed, its Solar System planet status may not be guaranteed. The reason: Astronomers theorize that Tyche could be a planet born in another star system and captured by ours.
http://m.gizmodo.com/5759865/the-mystery-o...ur-solar-system
Top
flyingbuttressman
Posted: Feb 14 2011, 07:06 PM


noblesse oblige / nullius in verba
*****

Group: Power Member
Posts: 5869
Joined: 8-June 09

Positive Feedback: 68.66%
Feedback Score: 166


QUOTE (Capracus @ Feb 14 2011, 02:03 PM)
Not exactly an exoplanet, but it may have been at one time
More:
http://www.dailymail.co.uk/sciencetech/art...lar-system.html

I'm trying to figure out why only a couple news sources are carrying this story. So far, all I've got are Gizmodo, DailyFail and the Independent.
Top
Capracus
Posted: Feb 15 2011, 09:13 AM


Advanced Member
*****

Group: Power Member
Posts: 5375
Joined: 5-October 06

Positive Feedback: 75.56%
Feedback Score: 41


QUOTE (flyingbuttressman @ Feb 14 2011, 07:06 PM)
I'm trying to figure out why only a couple news sources are carrying this story. So far, all I've got are Gizmodo, DailyFail and the Independent.
Appearently the story has been in the news for some time. Unfortunately, being products of an oppressive culture, we tend not to stay well informed on the current state of scientific advancement. If only we could be as enlightened as the readers of this publication.
http://www.tehrantimes.com/index_View.asp?code=231641
Top
flyingbuttressman
Posted: Feb 15 2011, 12:03 PM


noblesse oblige / nullius in verba
*****

Group: Power Member
Posts: 5869
Joined: 8-June 09

Positive Feedback: 68.66%
Feedback Score: 166


QUOTE (Capracus @ Feb 15 2011, 04:13 AM)
Appearently the story has been in the news for some time. Unfortunately, being products of an oppressive culture, we tend not to stay well informed on the current state of scientific advancement. If only we could be as enlightened as the readers of this publication.
http://www.tehrantimes.com/index_View.asp?code=231641

Here's a good follow-up to the original articles:
No, there’s no proof of a giant planet in the outer solar system
Top
Capracus
Posted: Feb 15 2011, 12:18 PM


Advanced Member
*****

Group: Power Member
Posts: 5375
Joined: 5-October 06

Positive Feedback: 75.56%
Feedback Score: 41


QUOTE (flyingbuttressman @ Feb 15 2011, 12:03 PM)
Here's a good follow-up to the original articles:
No, there’s no proof of a giant planet in the outer solar system
I don't think I've read an article claiming proof of the theory, and I've seen articles on the subject dating back nearly a year, but I'm sure if you stray into the conspiracy side shows, it's already considered as fact.
Top
flyingbuttressman
Posted: Feb 15 2011, 12:23 PM


noblesse oblige / nullius in verba
*****

Group: Power Member
Posts: 5869
Joined: 8-June 09

Positive Feedback: 68.66%
Feedback Score: 166


QUOTE (Capracus @ Feb 15 2011, 07:18 AM)
I don't think I've read an article claiming proof of the theory, and I've seen articles on the subject dating back nearly a year, but I'm sure if you stray into the conspiracy side shows, it's already considered as fact.

It's not that they're claiming false proof, it's that media organizations tend to exaggerate. The truth is that the original study said that there "could" be a large exoplanet in the Oort cloud. All the news organizations that picked up the story said "There might be a 9th planet after all."

Modern science journalism is shamefully inaccurate.
Top
Capracus
Posted: Feb 15 2011, 10:29 PM


Advanced Member
*****

Group: Power Member
Posts: 5375
Joined: 5-October 06

Positive Feedback: 75.56%
Feedback Score: 41


QUOTE (flyingbuttressman @ Feb 15 2011, 12:23 PM)
It's not that they're claiming false proof, it's that media organizations tend to exaggerate. The truth is that the original study said that there "could" be a large exoplanet in the Oort cloud. All the news organizations that picked up the story said "There might be a 9th planet after all."

Modern science journalism is shamefully inaccurate.
It's called a journalistic hook. Ideally an article can be titled in such a way to get maximum attention without sacrificing the validity of the story content. I think the mainstream press for the most part meets this standard, but admittedly some do fail, like this example:
QUOTE
Tyche: Meet the Mysterious New Super-Planet Said to Be in Our Solar System
http://www.aolnews.com/2011/02/14/tyche-me...o-be-in-our-so/


And if you consider everyone with a website to be a journalist, then the standard is essentially abandoned:
QUOTE
Jupiter is Not Longer The Biggest Planet in Our Solar System
http://scienceray.com/astronomy/jupiter-is...r-solar-system/





This post has been edited by Capracus on Feb 15 2011, 10:48 PM
Top
uaafanblog
Posted: Feb 18 2011, 02:49 AM


Advanced Member
*****

Group: Power Member
Posts: 1184
Joined: 27-November 06

Positive Feedback: 72.73%
Feedback Score: 80


While the so-called "journalists" that ran with this story bear some responsibility ultimately I think this Matese and Whitmire duo are the real problem here. They had their *** slapped into the dirt over these claims more than a few years ago yet they persist.

I'm sure we've all had the discussion with people illiterate to science who make the "it's just a theory" argument and/or don't understand the difference between the words "possibility" and "probability" .... well boobs like these two guys sure don't make it any easier when after I explain that these guys have no basis for their claims and have to hear the retort, "but they're scientists!"

Good scientists (in particular Cosmologists) should refuse to participate with media if anything they say is going to be selectively edited. I've seen some people I otherwise respect turn up in the worst sort of claptrap media seemingly saying *** that I know they didn't mean.


--------------------
I been stuffed in your pocket for the last hundred days, when I don't get my bath I take it out on the slaves. So grease up your baby for a ball on the hill, I'll polish them rockets now and swallow those pills and say ....
Ahhhhhh .... Spacelord mutha mutha.
-- Monster Magnet --

It is offensive and ruinous, something to be avoided at all cost, for a nonbeliever to hear a Christian talking about these things as though with Christian writings as his source, and yet so nonsensically and with such obvious error that the nonbeliever can hardly keep from laughing.
-- St. Augustine --

I laugh a lot in the Evolution/Creation section of this forum.
Top

Topic Options

Add reply · Start new topic · Start new poll


 

Terms of use