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Habitability in our solar system. Credit: UPR Arecibo, NASA PhotoJournal

Where Could Humans Survive in our Solar System?

Article Updated: 24 Dec , 2015

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If humans were forced to vacate Earth, where is the next best place in our solar system for us to live? A study by the University of Puerto Rico at Arecibo has provided a quantitative evaluation of habitability to identify the potential habitats in our solar system. Professor Abel Mendez, who produced the study also looked at how the habitability of Earth has changed in the past, finding that some periods were even better than today.

Mendez developed a Quantitative Habitability Theory to assess the current state of terrestrial habitability and to establish a baseline for relevant comparisons with past or future climate scenarios and other planetary bodies including extrasolar planets.

“It is surprising that there is no agreement on a quantitative definition of habitability,” said Mendez, a biophysicist. “There are well-established measures of habitability in ecology since the 1970s, but only a few recent studies have proposed better alternatives for the astrobiology field, which is more oriented to microbial life. However, none of the existing alternatives from the fields of ecology to astrobiology has demonstrated a practical approach at planetary scales.”

His theory is based on two biophysical parameters: the habitability (H), as a relative measure of the potential for life of an environment, or habitat quality, and the habitation (M), as a relative measure of biodensity, or occupancy. Within the parameters are physiological and environmental variables which can be used to make predictions about the distribution, and abundance of potential food (both plant and microbial life), environment and weather.

The image above shows a comparison of the potential habitable space available on Earth, Mars, Europa, Titan, and Enceladus. The green spheres represent the global volume with the right physical environment for most terrestrial microorganisms. On Earth, the biosphere includes parts of the atmosphere, oceans, and subsurface (here’s a biosphere definition). The potential global habitats of the other planetary bodies are deep below their surface.

Enceladus has the smallest volume but the highest habitat-planet size ratio followed by Europa. Surprisingly, Enceladus also has the highest mean habitability in the Solar System, even though it is farther from the sun, and Earth, making it harder to get to. Mendez said Mars and Europa would be the best compromise between potential for life and accessibility.

n Oct. 5, 2008.  Image credit: NASA/JPL/Space Science Institute  Cassini came within 25 kilometers (15.6 miles) of the surface of Enceladus o

n Oct. 5, 2008. Image credit: NASA/JPL/Space Science Institute Cassini came within 25 kilometers (15.6 miles) of the surface of Enceladus o


“Various planetary models were used to calculate and compare the habitability of Mars, Venus, Europa, Titan, and Enceladus,” Mendez said. “Interestingly, Enceladus resulted as the object with the highest subsurface habitability in the solar system, but too deep for direct exploration. Mars and Europa resulted as the best compromise between habitability and accessibility. In addition, it is also possible to evaluate the global habitability of any detected terrestrial-sized extrasolar planet in the future. Further studies will expand the habitability definition to include other environmental variables such as light, carbon dioxide, oxygen, and nutrients concentrations. This will help expand the models, especially at local scales, and thus improve its application in assessing habitable zones on Earth and beyond.”

Studies about the effects of climate change on life are interesting when applied to Earth itself. “The biophysical quantity Standard Primary Habitability (SPH) was defined as a base for comparison of the global surface habitability for primary producers,” Mendez said. “The SPH is always an upper limit for the habitability of a planet but other factors can contribute to lower its value. The current SPH of our planet is close to 0.7, but it has been up to 0.9 during various paleoclimates, such as during the late Cretaceous period when the dinosaurs went extinct. I’m now working on how the SPH could change under global warming.”

The search for habitable environments in the universe is one of the priorities of the NASA Astrobiology Institute and other international organizations. Mendez’s studies also focus on the search for life in the solar system, as well as extrasolar planets.

“This work is important because it provides a quantitative measure for comparing habitability,” said NASA planetary scientists Chris McKay. “It provides an objective way to compare different climate and planetary systems.”

“I was pleased to see Enceladus come out the winner,” McKay said. “I’ve thought for some time that it was the most interesting world for astrobiology in the solar system.”

Mendez presented his results at the Division for Planetary Sciences of the American Astronomical Society meeting earlier this month.

Source: AAS DPS

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Manu
Member
Manu
October 16, 2009 11:04 AM

Interesting study, although its alleged motivation just makes me mad.
Beginning with “If humans were forced to vacate Earth”, the next consideration should not be “where”, but “no way to move billions of people”. And so, there’s no point to it, at all.

[/rant]

Lawrence B. Crowell
Member
Lawrence B. Crowell
October 16, 2009 12:44 PM

Hmmm…, I think this is far more outlandish than the multiverse idea. Habitability areas on other planets? Maybe, for prokaryotic type of life, but for us? I don’t think so. This might be applicable to the notion of life in general, though to be honest I think there are matters of complexity here. The size of a system is a measure of the maximum complexity it can have. So while there might be life, I doubt it is very complex.

LC

Jon Hanford
Member
Jon Hanford
October 16, 2009 1:30 PM

I agree with Manu and Crowell on this one. This theory is based on “two biophysical parameters” to search for habitats fit or adaptable for/by humans. What about the resources and engineering to move humanity into the solar system? How’s that gonna work?

HeadAroundU
Member
October 16, 2009 4:48 PM

You guys make me sad. LC has a serious depression so it’s expected from him. We don’t have to move the whole humanity. Just me and about 1000 hot women. We will leave LC die here because he is old and depressed.

Lawrence B. Crowell
Member
Lawrence B. Crowell
October 16, 2009 5:03 PM
It is not depression, it is a matter of reality. I am all for sending probes to look for life on other planets and moons. I have no problem with humans in space to facilitate maintenance of systems, such as the recent Hubble repair mission. I do have problems with fantasies about moving off to other planets, particularly when such people imagine escaping Earth. Take my word for it, there is no environment out there which is remotely comparable to Earth’s. It means we need to take stock of our situation on this planet and start figuring out how we can stop fouling it up. Which sounds like a more practical effort? Either we figure out how to… Read more »
Astrofiend
Member
Astrofiend
October 16, 2009 5:17 PM

“We don’t have to move the whole humanity. Just me and about 1000 hot women.”

Who’ll soon turn into 1000 raging banshees when they realise that there is no shopping, next top model or facebook off-world… Good luck!

HeadAroundU
Member
October 16, 2009 5:48 PM
I don’t like you and that’s very kindly said. “If humans were forced to vacate Earth” That sentence is out of place. A cheap way to gain some new readers on UT. This is a science towards future. We don’t need it now but why not? We WILL need it one day. It’s not insane as Drake equation for example. I don’t see how it is comparable to multiverse. We will move out one day for whatever reasons. Take it as a fact. But of course a lot of people will stay here. “I have no problem with humans in space to facilitate maintenance of systems, such as the recent Hubble repair mission.” LOL. It’s very strange to… Read more »
William928
Member
William928
October 16, 2009 6:51 PM

@HeadAroundU:
It appears that you’re taking some meanspririted and unwarranted shots at LC. If you’ve read any of his previous posts, I think you’d regret your political attacks on his character, which from where I sit are entirely baseless. His comments consistently are intelligent, and I for one learn something almost every time I read them. I’m not sure what your motivation is in these attacks, but it seems at the least to be unprofessional, and very unnecessary. If you have a genuine disagreement with someone’s comments, offer your rebuttal in a professional argument. Personal attacks have no place in this forum.

Vanamonde
Guest
Vanamonde
October 16, 2009 7:13 PM
For a very long time, I was optimistic about O’Neal’s ideas about colonies at L5 and other places, being the best hope for humankind, the most positive answer to the population bomb. Once you have expended all that energy to get out of this 1 gee gravity well, why slide down another while you can build a home design to fit you exactly in a solar orbit that provide all your energy needs for the next few billion years? I was a High Frontier advocate. Then Marshall Savage came out with his “The Millennial Project: Colonizing the Galaxy in Eight Easy Steps”. Unlike O’Neal, many of his ideas depended on new techologies yet to be developed BUT he… Read more »
damian
Member
October 17, 2009 12:00 AM
I also think that once human beings figure out how to survive in zero gravity there will be little desire the go back down a gravity well. Building small scale versions of earth (habitats) in the so called habitable zone of space that we currently occupy is the logical step. As I see it we already have the technical means to achieve such space habitats, the problem is the raw materials. Capturing Water rich asteroids is one solution. Converting them is however a long term engagement, one that may require generations of development. I was recently fascinated by zero g experiments with water on the space station. The first experiment towards a viable habitat in space might well… Read more »
Lawrence B. Crowell
Member
Lawrence B. Crowell
October 17, 2009 4:43 AM
No I am not conservative, and in fact worked on the Obama campaign. To be honest I think the Republicans are going psychopathic. On the other hand I do think there needs to be a responsible conservative polity, but conservatives have completely blown a head gasket as I seen it. Yet on the whole I am on the progressive side of things. The dream of humanity moving into space and becoming in a sense “astro-beings” is rather compelling, and Star Trek series held a captive audience for a long time. Yet as indicated above, moving into space is not going to take the pressures off our problems on Earth. The idea of moving some small number of people… Read more »
Manu
Member
Manu
October 17, 2009 7:27 AM
@ Vanamonde: please explain how you relate the Joss Whedon quote to this: “But not all of us. The species can survive and for the long term, having many cities in the space will enhance our survivablity.” Where is equality when you split humanity towards such different futures, specifically when the minority’s goal is survivability? What’s the point of species survival if it’s at the expense of equality? Joss Wheldon: “Equality is like gravity. We need it to stand ON THIS EARTH as men and women…” This exactly sums up my feelings about the whole thing. Thanks anyway for the quote which I didn’t know. @ damian: a nice democratic society you envision here. Please count me out.… Read more »
HeadAroundU
Member
October 17, 2009 9:20 AM

@William
It’s all warranted and clear. He seems intellingent but that’s not everything. There’s more and that more in his head is broken. It affects him in a bad way. It’s incompatible with a scientist. He is offensive towards common believes and I dare to say knowledge. Somebody has to tell him, professionally or not, so he can get better.

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
October 17, 2009 7:58 PM
Hrm! This is old news, and Mendez research is both extensive and in directed towards identifying biospheres by their habitability. Nancy’s headline and ingress is not from the press release. Let me quote my comment from 8th Oct (on Europa’s capability to support life): Regarding habitability I haven’t read much, but the earlier modeling efforts I’ve seen have been Drake equation type estimates. However, Mendez have developed quite a nice quantitative method, where Mars and Europa places just behind Earth in global habitability, based on planetary models. […] I haven’t caught up with the solar system part of the research, but the earlier work seems sound. By modeling land plant environmental responses Mendez matches Earth detailed Net Primary… Read more »
Mr. Man
Member
Mr. Man
October 17, 2009 1:02 PM

I see what mr. HeadAroundU is TRYING to say, LC.
Maybe he threw a few too many pot shots at you,
But I think he just wants you to be a little more open minded.

The people that write these articles are, afterall, experts, they know what their talking about and if they say we have a chance to expand, why should we try to prove them wrong. I mean, Do you really think MULTI-Verses are less far-fetched than living on nearby planets. you can, I’m just saying thats…different. Not that there is anything wrong with being far-fetched anyhow, everything was once when you think about it.
Best,
Mr. Man

damian
Member
October 17, 2009 5:21 PM
Interesting. It is a SciFi dream, for our generation. And the trailing comments underly the root of the problem in terms of realizing the dream. The simple fact is that our (democratic) system will not function in a space habitat. And our capitalist system will never build the thing in the first place. But this unfounded fear of change as (necessarily) substituting our personal freedom is unfounded. There are only 2 ways that it will ever happen. One is if a global consensus occurs and funds a long term vision, or a private corporation undertakes the task. In either scenario, in the short term, the people that will work on building such a product will need to agree… Read more »
Mr. Man
Member
Mr. Man
October 17, 2009 5:46 PM

@damian
It is true, that democracies can be awefully indescisive, with politicians saying this and doing something completely different (YOU KNOW WHO YOU ARE!) but we can do great things….we reached the moon before communist Russia, don’t forget. We just need a good, decisive ruler and an ambitious, risk-taking populace.
Mr. Man

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
October 17, 2009 8:20 PM
@ Vanamonde: he enlighten me to the fact, that if the ENTIRE industrial output of our present day world was redirected to moving people off planet, it STILL would not keep up with the birth rate. More exactly, if the industrial output was redirected at our current birth rate, it wouldn’t help to stabilize the human population. However, IIRC our present day world is likely on a path to stabilization, thanks to observed improvements in technology, economy and politics. (Less poverty, better medicine and more education leads to fewer children.) I believe that UN project this will happen ~ 2030. Most likely the population will decrease substantially before settling to a steady state. Numbers like ~ 1-3 G… Read more »
Lawrence B. Crowell
Member
Lawrence B. Crowell
October 18, 2009 5:36 AM
It appears that some of these issues are being fleshed out here. There are a number of things which need to be considered. I think an important one is to knock down the Panglossian idea that economic systems are rational. Economic systems operate according to dopamine, endorphins, serotonin, hormones and other neurotransmitters and psychological changing chemicals. The propaganda wing of our economies, called advertising, drives people to buy based on probable elevations of dopamine levels to give a sense of reward and pleasure. Studies with rhesus monkeys have demonstrated that conditioning can cause dopamine release before a reward, food or sweet drinks, based on conditioning. It is a version of Pavlov’s dogs. Other adverts invoke fear, “If you… Read more »
Maxwell
Member
Maxwell
October 18, 2009 6:52 AM
Humans are just becoming aware of the planets limits and the results of doing business on such a massive scale. The technology to measure our environment is just coming online and we still aren’t sure what the results mean. Its a lot to take in on such a short time scale. So far as humanity in space, if we ever do get to living up there you can be sure that the laws of that society will be fairly strict and have more in common with the middle ages than modern America. People living under stressful situations are less likely to think about high ideals and to be more concerned with putting food and water on the table.… Read more »
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