60 years of silence - so far

[bilby]

We are here because people didn't like Europe and wanted to go elsewhere. I think interstellar colonization will happen the same way

What, with foolish people who massively underestimated the distances involved getting incredibly lucky and finding out that there's an entire unknown solar system half way between here and Proxima Centauri?

With interstellar travellers surviving by catching interstellar fish, mammals and birds for food, and stopping at interstellar islands to top up their water (and air) supplies?

With colonists finding that the new planets on which they land are not only stocked with edible plants and animals (and drinkable water and breathable air), but inhabited by native humans who can help them to determine what is (and is not) safe to eat?

The whole analogy breaks down on the vast distances, and massively inimical environment that fills those distances.

Columbus was a fool, who got lucky. But he wasn't attempting to cross an ocean that was not a couple of month's voyage, but a couple of decades; He didn't have to take his own air with him; He didn't have to take enough food and water not only for the voyage, but also for the entire stay in the Caribbean, plus the trip back.

Interstellar colonisation is science fiction. Notice that we never colonised Antarctica, and Antarctica is VASTLY more accessible and VASTLY more hospitable than any exoplanets are likely to be.

Your analogy handwaves away a collection of problems that we may never be able to solve, and which we certainly will never be able to solve cheaply enough to make mere malcontent a sufficient inspiration to overcome these challenges.

Shit, it took a decade of concerted effort by both of the world's superpowers working in direct competition with each other, to get a dozen people to the Moon and back. And nobody's been there since.

We might, just possibly, one day establish a Moon colony. A Mars colony is rather less likely. Leaving the inner Solar System, much less travelling to another star, is cloud cuckoo land fantasy; Colonising another star system is cloud cuckoo land fantasy cubed.

 

[lpetrich]

Considering colonization, the colonization of our planet was far from trivial. Our species originated in Africa, and that continent is warm all year. A Major Change in Rate of Climate Niche Envelope Evolution during Hominid History - PMC

Looking at the earlier species after the split of our ancestors from the ancestors of chimps, like Australopithecus species, the article says "... the predicted range in annual temperatures spans from 20°C (coldest quarter of the year) to 29.9°C (warmest quarter) and in mean rainfall from 12 mm (driest quarter) to 512 mm (wettest quarter)."

Aridity - an overview | ScienceDirect Topics notes C. Holzapfel, in Encyclopedia of Ecology (Second Edition), 2008 -- Definition of Deserts

By how much precipitation:

• Extreme arid: less than 60–100 mm/yr
• Arid: from 60–100 to 150–250 mm/yr
• Semiarid: from 150–250 to 250–500 mm/yr
• Nonarid: more than 500 mm/yr

Looking at  Nairobi Kenya, a city in the climate zone where we emerged, its average low temperature is 13 C and its average high temperature 25 C, varying only a few degrees over the year. Precipitation: 745 mm/yr

Closer to the present, the first of Homo erectus left Africa around 1.5 million years ago and spread as far north as Southern Europe and Northern China. From the article, "... the corresponding figures are 0.7°C–31.9°C for temperature range and from 4.8 mm to 1080 mm for precipitation range."

Checking on the climate of  Marseille France, its climate is very seasonal, with mean temperature ranging from 4 to 12 C in January to 20 - 31 C in July. Precipitation: 532 mm/yr.  Beijing China is the home of the Zhoukoudian caves, with some notable H. erectus remains, and its climate is also seasonal: ranging from -7 to 2 C in January to 23 to 32 C in July. Precipitation: 528 mm/yr. These are all Holocene values, and these places likely had similar climates in previous interglacials.

So the erectines must have made clothes for themselves, though likely simple clothes, like animal-skin cloaks.

Getting closer with Homo heidelbergensis (700 thousand years ago) and Homo neanderthalensis (400 thousand years ago) From the article, "... the estimates for annual temperature extremes span from minus 21.1°C to plus 31.4°C and for annual precipitation from 0.7 mm to 905 mm."

Looking at the northern edge of the Neanderthals' range, I find  London UK, seasonal climate: 3 to 8 C in January to 14 to 24 C in July, precipitation 615 mm/yr,  Prague Czechia, seasonal climate: -2 to 3 C in January to 14 to 25 C in July, precipitation 587 mm/yr,  Sevastopol Ukraine, seasonal climate: 0 to 5 C in January to 18 to 26 C in July, precipitation 379 mm/yr,  Almaty Kazakhstan, seasonal climate: -8 to 0 C in January to 9 to 30 C in July, precipitation 674 mm/yr. Holocene, of course. Though they were likely colder during the last Ice Age, especially London.

Neanderthals must also have been clothed.

That temperature limit also explains why they never made it into the Americas -- northern Siberia was too cold for them, so they could not get to Beringia.

Turning to our present species, with Paleolithic technology we went far to the north.  Murmansk Russia, seasonal climate: -13 to 6 C in January to 10 to 18 C in July, precipitation 529 mm/yr,  Norilsk Russia, seasonal climate: -31 to -24 C in January to 10 to 18 C in July, precipitation 341 mm/yr,  Utqiagvik formerly Barrow, Alaska, US, seasonal climate: -28 to -21 C in January to 2 to 9 C in July, precipitation 137 mm/yr,  Iqaluit formerly Frobisher Bay, Nunavut, Canada, seasonal climate: -31 to -23 C in January to 4 to 12 C in July, precipitation 404 mm/yr,  Nuuk formerly Godthaab, Greenland, seasonal climate: -10 to -5 C in January to 4 to 11 C in July, precipitation 853 mm/yr.

 

[steve_bank]

The three most important things on real estate are location, location, location.

The three most important things about space travel are energy, energy, energy.

 

[Jimmy Higgins]

Sure, we have this drive to expand out, but you get to a point where you can't exceed the limits. Like how a long jumper can jump nearly 30 feet! But isn't jumping the Grand Canyon. Space travel is a long jumpers Grand Canyon. We could figure out suspended animation, fraction of light-speed travel, shielding, oxygen, food replication... but to ensure:
1) it (any number of critical processes in which a single one of them could doom the mission) doesn't breakdown
2) we don't breakdown while living in a fish tank we can't escape

And this is to go out and venture where we haven't a clue regarding whether there is anything remotely suitable for breathing, eating, energy? Requiring effectively a self-sustaining ship.

The three most important things on real estate are location, location, location.

The three most important things about space travel are energy, energy, energy.

Energy is crucially important, but redundancy is even more important, while traveling in our fish tanks in space.

Anything I think we do that is extra-solar system will be probes.

 

[steve_bank]

If there are a lot of ETs like us then the universe will be clutteed with all those space probes

The reason solar systems are so far apart is to prevent the spread of invasive species.

 

[Jimmy Higgins]

If there are a lot of ETs like us then the universe will be clutteed with all those space probes

Would it? Space is big. The Milky Way is 17 trillion cubic light years (or 12.3 US Texas gallons) in size and contains roughly 100 billion stars. Let's assume every star has one planet with intelligent life capable of sending probes. And we'll assume each of these planets sends out 100,000 probes. That means for every 1.4x10³⁶ km³, of the Milky Way, there would be one probe. That breaks down to a cube that 1.1x10¹² km in length, width, etcth.

That'd be less than one probe within our solar system (including the Oort Cloud). Our universe could be chock full of probes... and we'd never even know.

The reason solar systems are so far apart is to prevent the spread of invasive species.

 

[bilby]

If there are a lot of ETs like us then the universe will be clutteed with all those space probes

Maybe it is.

Up until a few years ago, we didn't even know for sure whether other stars even had planets. Space is a big place, and even if it were riddled with space probes, we would need to be astonishingly lucky to spot one, and even luckier to be able to say with any confidence that that was what it was.

 

[Shadowy Man]

If there are a lot of ETs like us then the universe will be clutteed with all those space probes

Maybe it is.

Up until a few years ago, we didn't even know for sure whether other stars even had planets. Space is a big place, and even if it were riddled with space probes, we would need to be astonishingly lucky to spot one, and even luckier to be able to say with any confidence that that was what it was.

If you believe Avi Loeb then Ouamoua (sp?) was one.

 

[Loren Pechtel]

Sure, we have this drive to expand out, but you get to a point where you can't exceed the limits. Like how a long jumper can jump nearly 30 feet! But isn't jumping the Grand Canyon. Space travel is a long jumpers Grand Canyon. We could figure out suspended animation, fraction of light-speed travel, shielding, oxygen, food replication... but to ensure:

Lightsail can give 1% of lightspeed.

1) it (any number of critical processes in which a single one of them could doom the mission) doesn't breakdown
2) we don't breakdown while living in a fish tank we can't escape

Energy is crucially important, but redundancy is even more important, while traveling in our fish tanks in space.

Anything I think we do that is extra-solar system will be probes.

Yup, redundancy. You have as few critical systems as possible. Most systems can be built on a basis of many smaller units provisioned for some attrition. I would think it would come down to the hull, the drive and whatever protects you from cosmic dust.

 

[bilby]

I would think it would come down to the hull, the drive and whatever protects you from cosmic dust.

Those are three of the many problems we would need to solve, and none yet has a solution that doesn't require us finding and exploiting large deposits of unobtanium or handwavium.

 

[lpetrich]

Comparing to Earth colonization, colonizing other planets in a planetary system is much more difficult, and colonizing planets of other stars' planetary systems is even more difficult.

Of our colonization efforts on our planet, sea voyaging offers the closest analogy. You and your fellow colonists are stuck inside a vehicle for several days at least, a vehicle surrounded by a hostile environment. The Polynesians' colonization voyages are the best analogy of these, by distance traveled relative to level of technology. But once they arrived at new land, they could live as they had lived in their earlier homes, growing their crops and raising their domestic animals in warm climates.

That is not possible for us for the rest of the Solar System and for most of most other planetary systems, unless one has already done some space colonization. Outer space is a vacuum by ordinary standards, and all the smaller celestial bodies are airless. Of those with atmospheres, Venus is too hot, Mars, Titan, Triton, and Pluto are too cold, and the four outer planets' atmospheres have no condensed surface, no solid or liquid surface. Venus and Mars have mostly CO2 in their atmospheres, while Titan, Triton, and Pluto mostly N2 with some CH4 and for Pluto some CO (carbon monoxide).

 Extraterrestrial atmosphere has a nice diagram of the planets and larger moons plotted as functions of their surface temperatures and escape velocities. One can calculate an "atmosphere factor":

(escape velocity)² / (temperature)

Everything with an atmosphere factor larger than Titan's has an atmosphere, and everything with an atmosphere factor smaller than Mercury's lacks an atmosphere, but there is a sizable gap in between. Jupiter's four big moons are all in that gap, and they are all airless. Mercury, though airless, has an atmosphere factor close to those of Triton and Pluto,

So it may be rather nontrivial to predict what kind of atmosphere a planet will have.

 

[lpetrich]

• Venus: radius = 6051.8 km, escvel = 10.36 km/s, grav = 0.904 ge, press = 93 bar, temp = 462 C / 735 K, comp = CO2 96.5%, N2 3.5%, ...
• Earth: radius = 6371.0 km, escvel = 11.186 km/s, grav = 1 ge, press = 1.013 bar, temp = 15 C / 288 K, comp = N2 78.084%, O2 20.946%, Ar 0.9340%, CO2 0.0280% (preindustrial), 0.0417% (present)
• Moon: radius = 1736.0 km, escvel = 2.38 km/s, grav = 0.1654 ge, essentially no atmosphere
• Mars: 3389.5 km, escvel = 5.027 km/s, grav = 0.3794 ge, press = 0.00610 bar, temp = -63 C / 210 K, comp = CO2 95%, N2 2.8%, Ar 2%, 02 0.174%, CO 0.0747%
• Titan, moon of Saturn: radius = 2574.73 km, escvel = 2.641 km/s, grav = 0.138 ge, press = 1.5 bar, temp = -179.5 C / 93.7 K, comp = N2 94.2%, CH4 5.65%, N2 0.099%, Ar 0.0043%
• Triton, moon of Neptune: radius = 1353.4 km, escvel = 1.455 km/s, grav = 0.0794 ge, press = 1.4 to 1.9 * 10^-5 bar, temp = -235 C / 38 K, comp = N2 ~100%, CH4 ~ 0.01%, CO ~ 0.01%
• Pluto: radius = 2376.6 km, escvel = 1.212 km/s, grav = 0.063 ge, press = 10^-5 bar, temp = -229 C / 44 K, comp = N2 ~100%, CH4 0.25%, CO 0.07%

So most of the Solar System is uninhabitable for us, unless we use the sort of protection that we must use in interplanetary space. No place has a nice temperature for us, except if one goes ballooning in Venus's clouds. Even then, Venus has the problem of having mostly CO2 in its atmosphere with only a tiny amount of O2.

Looking back in time in our planet's history, one finds that we could have plenty of oxygen to breathe only as far back as the Cambrian period, some 500 million years ago, and that it was much less before then. CO2 decreased over time, from being much of the atmosphere in the Earth's earliest days, and N2 stayed roughly constant.

Reconstructing Earth’s atmospheric oxygenation history using machine learning | Nature Communications
Enigmatic evolution of microbial nitrogen fixation: insights from Earth’s past: Trends in Microbiology

From the Ediacaran Period to the present, our planet had a breathable amount of O2, but before the Ediacaran, it was much less, some 10^-4 to 10^-1 of Present Atmospheric Level (PAL) over the "Boring Billion", much of the Proterozoic Eon. It was somewhat higher during the Great Oxygenation Event (some 2.5 to 2.0 billion years ago), and much lower before then.

By comparison, the least oxygen amount on the present-day surface is at the peak of Mt. Everest, 1/3 PAL. It's borderline survivable, and main climbers of that mountain bring their own oxygen.

So even if a planet is very Earthlike, its atmosphere may be unbreathable to us -- that's what our homeworld itself was like for much of its existence.

 

[bilby]

From the Ediacaran Period to the present, our planet had a breathable amount of O2

The limiting factor on human survival (and comfort) was likely CO₂.

There doesn't need to be very much of it for the atmosphere to be unbreathable for humans, even in the presence of plentiful oxygen.

 

[DBT]

Looks like Earth is our only home in the foreseeable future.

 

[lpetrich]

 Carbon dioxide in Earth's atmosphere and  Hypercapnia

In the Cambrian Period, some 500 million years ago, atmospheric CO2 was about 0.5% the present total atmosphere, or a partial pressure of 5 millibar (0.005 bar). That has some effects, but not very strong effects. We could easily survive breathing Cambrian air, and likely also Ediacaran air.

 

[bilby]

 Carbon dioxide in Earth's atmosphere and  Hypercapnia

In the Cambrian Period, some 500 million years ago, atmospheric CO2 was about 0.5% the present total atmosphere, or a partial pressure of 5 millibar (0.005 bar). That has some effects, but not very strong effects. We could easily survive breathing Cambrian air, and likely also Ediacaran air.

Breathing air with 0.5% or more of carbon dioxide is OK for short periods, but you're going to feel pretty seedy - headache , dizziness, nausea - if you have to do it on a long term basis.

Trace gases (including, but not limited to, carbon dioxide) could easily render an oxygen rich exoplanetary atmosphere unbreathable to humans.

Most are unlikely to be present unless a biological process is generating them, because in the absence of such processes they're going to react with other substances in the environment and be removed from the atmosphere, and are unlikely to be replenished. But then, that's true of oxygen, too.

Any oxygen rich atmosphere is almost certainly a consequence of life. However, there's no particular reason to think that alien life would not generate other toxic gases (and oxygen is certainly a toxic gas, even though Earthbound life has evolved to tolerate and even depend upon it).

An exoplanet that has an atmosphere of 78% Nitrogen and 20% oxygen could easily be uninhabitable by humans if the remaining 2% were to include a certain amount of chlorine, for example. Or of carbon monoxide. Or of a fairly large range of organic poisons, that might hypothetically be deployed by the local biology as a competitive edge over evolutionary rivals.

The terrestrial biochemistry to both produce and tolerate oxygen was a major boost for the species that first evolved that pair of abilities, and oxygen production now dominates the plant kingdom and is common in such widespread life forms as phytoplankton; while oxygen tolerance is almost completely universal amongst terrestrial organisms.

An exoplanet on which Cl₂ production and tolerance were similarly widespread, would be a very unpleasant place for humans, and for their crops and livestock.

 

[steve_bank]

https://www.cnn.com/2023/09/12/world/habitable-zone-exoplanet-ocean-webb-telescope-scn/index.html

CNN —

Waters may be flowing on the surface of a colossal planet that lies about 120 light-years from Earth, according to new evidence uncovered by the James Webb Space Telescope.

 

[Loren Pechtel]

An exoplanet that has an atmosphere of 78% Nitrogen and 20% oxygen could easily be uninhabitable by humans if the remaining 2% were to include a certain amount of chlorine, for example. Or of carbon monoxide. Or of a fairly large range of organic poisons, that might hypothetically be deployed by the local biology as a competitive edge over evolutionary rivals.

The terrestrial biochemistry to both produce and tolerate oxygen was a major boost for the species that first evolved that pair of abilities, and oxygen production now dominates the plant kingdom and is common in such widespread life forms as phytoplankton; while oxygen tolerance is almost completely universal amongst terrestrial organisms.

An exoplanet on which Cl₂ production and tolerance were similarly widespread, would be a very unpleasant place for humans, and for their crops and livestock.

Are any of those stable, though? Most of the nasty stuff is rather reactive, would it stay in the atmosphere if something widespread wasn't continually producing it? Even oxygen can only exist in the atmosphere due to production, it is eliminated by reaction but slowly enough that the vast quantities pumped out by photosynthesis can maintain the supply of oxygen.

The non-reactive toxic stuff isn't exactly prone to sticking around in the atmosphere.

 

[bilby]

An exoplanet that has an atmosphere of 78% Nitrogen and 20% oxygen could easily be uninhabitable by humans if the remaining 2% were to include a certain amount of chlorine, for example. Or of carbon monoxide. Or of a fairly large range of organic poisons, that might hypothetically be deployed by the local biology as a competitive edge over evolutionary rivals.

The terrestrial biochemistry to both produce and tolerate oxygen was a major boost for the species that first evolved that pair of abilities, and oxygen production now dominates the plant kingdom and is common in such widespread life forms as phytoplankton; while oxygen tolerance is almost completely universal amongst terrestrial organisms.

An exoplanet on which Cl₂ production and tolerance were similarly widespread, would be a very unpleasant place for humans, and for their crops and livestock.

Are any of those stable, though? Most of the nasty stuff is rather reactive, would it stay in the atmosphere if something widespread wasn't continually producing it? Even oxygen can only exist in the atmosphere due to production, it is eliminated by reaction but slowly enough that the vast quantities pumped out by photosynthesis can maintain the supply of oxygen.

The non-reactive toxic stuff isn't exactly prone to sticking around in the atmosphere.

You answered your own question.

Terrestrial life has evolved to produce a pretty vicious poison - oxygen - and to tolerate it. As a consequence, the Earth has a very unusual atmosphere, which contains almost 20% of a molecule that is only present because of terrestrial life.

An exoplanet without life would not be expected to have an oxygen rich atmosphere; Conversely, an exoplanet with alien life could easily have an atmosphere that is rich, not only in oxygen, but also in other unstable toxic chemicals, such as (for example) chlorine.

Such an atmosphere would be inimical to terrestrial organisms, despite its oxygen content.

There's no good reason to expect any exoplanet to have an atmosphere that humans can breathe. Our atmosphere is basically a part of the global extended phenotype; It's a reflection of the biosphere that maintains it in its current composition - and it has changed repeatedly over time as various biological factors have come and gone.

Right now, humans are pushing up the carbon dioxide level. What effect that will have on our species survival remains to be seen. But there's no doubt that a hypothetical time traveller could go to Earth's past and find the air unbreathable, and no reason to expect that the same won't be true at some (hopefully distant) future date. And if the very atmosphere shaped by Earth-like organisms is only occasionally able to support H. Sapiens, the idea of an exoplanetary atmosphere being able to do so, at any random time in its lifecycle, is absurd.

To travel for decades through the instantly lethal void of space would be bad enough, but even worse for any proposed colony is to get to your new outpost, only to find that you're still confined to (and utterly dependent upon the ongoing integrity of) your spacecraft or cumbersome suits, because there is no breathable air.

And you need to enclose your crops and supply them with earth air, and earth soil, because the local soil bacteria would rapidly poison the air if you used it.

Sterilising megatonnes of topsoil and then seeding it with terrestrial microbes and other organisms sounds like a lot of hard work. Probably better to just stick to trying to colonise Antarctica or Siberia.

 

[Shadowy Man]

https://www.cnn.com/2023/09/12/world/habitable-zone-exoplanet-ocean-webb-telescope-scn/index.html

CNN —

Waters may be flowing on the surface of a colossal planet that lies about 120 light-years from Earth, according to new evidence uncovered by the James Webb Space Telescope.

Been a long time coming, doing proper spectroscopy of exoplanets. Nice to see this field finally coming into its own.