Super-Earth civilization

[Noclevername]

If a sapient species develops an industrial society on a high gravity planet, could it plausibly colonize space? Reaching space would be extremely difficult by itself, and replicating the physical conditions of their world on a space station could be a nightmare. We have yet to do so despite nearly 6 decades of spaceflight, how much harder for heavyworlders?

[Roger E. Moore]

Posted a few articles on this topic, will find the links. In short, it could be nearly impossible using chemical rockets to get into space.

[Roger E. Moore]

Forgive posting three links at once, but these were relevant. The larger issue is, unless we have access to enormous lifting power that is relatively cheap, colonizing heavy planets is a bad idea, and exploring them (at least with sample returns) will be costly. This turns out to apply to any planet in a deep gravity well, and a super-Earth close to its sun-star will be a very hard place to reach and return from. On a side note, just getting a probe to return from the innermost Galilean moons of Jupiter (assuming it is not a flyby) will be tough.

All that said, the medical problems of living on a heavy planet could be prohibitive. Nothing wrong with sending down an ecology tailored for a heavy planet, if the planet is not inhabited, but no one is going there and coming back.

===============

https://arxiv.org/abs/1804.03698

Interstellar Escape from Proxima b is Barely Possible with Chemical Rockets

Abraham Loeb (Harvard) (Submitted on 10 Apr 2018)

A civilization in the habitable zone of a dwarf star might find it challenging to escape into interstellar space using chemical propulsion.

=================

https://arxiv.org/abs/1804.04727

Spaceflight from Super-Earths is difficult

Michael Hippke (Submitted on 12 Apr 2018 (v1), last revised 18 May 2018 (this version, v2))

Many rocky exoplanets are heavier and larger than the Earth, and have higher surface gravity. This makes space-flight on these worlds very challenging, because the required fuel mass for a given payload is an exponential function of planetary surface gravity. We find that chemical rockets still allow for escape velocities on Super-Earths up to 10x Earth mass. More massive rocky worlds, if they exist, would require other means to leave the planet, such as nuclear propulsion.

=================

https://arxiv.org/abs/1808.08141

Limitations of Chemical Propulsion for Interstellar Escape from Habitable Zones around Low-Mass Stars

Manasvi Lingam, Abraham Loeb (Submitted on 24 Aug 2018)

The habitable zones of low-mass stars are characterized by escape speeds that can be a few times higher than the Earth's orbit around the Sun. Owing to the exponential dependence of the required fuel mass on the terminal speed for chemical rockets, interstellar travel may not be easy for technological species inhabiting planets around M-dwarfs.

[grant hutchison]

If a sapient species develops an industrial society on a high gravity planet, could it plausibly colonize space? Reaching space would be extremely difficult by itself, and replicating the physical conditions of their world on a space station could be a nightmare. We have yet to do so despite nearly 6 decades of spaceflight, how much harder for heavyworlders?

Rather than rocketry, they might need to go for a "space fountain" - a tower supported by a high velocity particle stream. Robert Forward used one to get his aliens into space from the surface of a neutron star, in Dragon's Egg.

Grant Hutchison

[alromario]

Even worse off than ourselves.
“Enjoy your swim”.

The universe appears to extinguish life rather than harbour it, in the long run.

[Noclevername]

The universe appears to extinguish life rather than harbour it, in the long run.

Nonsense, we're here. Our whole planet is bursting with life.

The Universe has some bad neighborhoods, is all. OK, so they make up almost all of known space, but we cannot say what else is out there. The reason we don't see life yet could be due to the immense, unimaginable distances involved and the innate difficulties of detecting life.

Or we could be all there is, but that's still not nothing.

[Roger E. Moore]

I was thinking one general trend on higher gravity terrestrial worlds would be for life to be shorter, fighting gravity less. If four or more legs, shorter distances between the legs to reduce backbone strain. Bipedal would work well for intelligent beings, but elephantine (trunk/nose/arm) would work, too. Bigger heart and better pumping for circulatory system, too.

[Noclevername]

I was thinking one general trend on higher gravity terrestrial worlds would be for life to be shorter, fighting gravity less. If four or more legs, shorter distances between the legs to reduce backbone strain. Bipedal would work well for intelligent beings, but elephantine (trunk/nose/arm) would work, too. Bigger heart and better pumping for circulatory system, too.

Well, look at humans. We evolved on a world where most mammals, even smaller ones, have to go on all fours to support their weight. Even our closest relatives knuckle-walk. Yet we defied gravity to get vertical, balancing precariously on an inherently dynamically unstable arrangement of limbs that requires constant effort to stay upright. Madness!

Evolution is a funny beast. Even right here on Earth. Alien life, who knows? They might not even have legs. Or a heart.

[geonuc]

It might be plausible if the planet they inhabit is super abundant in the natural resources required to make chemical rockets, and they're easy to get at. Plus, they'd probably have a well developed industry for on-planet transportation to cope with the higher gravity, so getting stuff into orbit might not be any more difficult than it is for humans.

[Noclevername]

It might be plausible if the planet they inhabit is super abundant in the natural resources required to make chemical rockets, and they're easy to get at. Plus, they'd probably have a well developed industry for on-planet transportation to cope with the higher gravity, so getting stuff into orbit might not be any more difficult than it is for humans.

If they are multi-celled life, or biological life of similar complexity, they would have a high energy body chemistry and metabolism, so they'd need some form of oxidizer or catalyst. And for an atmosphere to hold enough oxygen or other combustible chemical to allow for such life, it'd have to be fairly dense, and so an additional impediment to launch.

Same goes for the industries need to build rockets, let alone other methods of space launch, sufficient to reach orbit. And liquid-breathing life would naturally find it even harder.

Of course, complex life might exist with none of these factors. Perhaps intelligent life is anaerobic but works on a slow scale, conserving energy. Perhaps it could have thin air but be based on an exotic enough chemistry not to need a dense atmosphere. It could have conditions or follow a tech tree that allows for industry without fire. There are endless variables.

But life here is based on organic chemistry common in space, and common to everywhere we've been able to extend our senses. It seems likely that such chemistry could be the most common basis for life elsewhere, assuming such exists. After all, we already know that such biochemistry works, and can develop on a high gravity terrestrial. And if it is life based on similar common chemistry, it'll need abundant oxidizer or equivalent, to reach the levels of complexity and energy use for intelligence.

[profloater]

On Earth birds have evolved hollow bones to reduce weight and we could expect similar structures to evolve just as we use holes in beams to lower weight on aircraft. Main struts, such as leg bones would be stronger if larger and hollowed out so we could imagine more Complex struts with muscles working through gaps instead of external fixtures. We already use muscle contractions in our legs to assist the heart in lifting blood. So evolution would introduce more designs.

[grant hutchison]

If they are multi-celled life, or biological life of similar complexity, they would have a high energy body chemistry and metabolism, so they'd need some form of oxidizer or catalyst. And for an atmosphere to hold enough oxygen or other combustible chemical to allow for such life, it'd have to be fairly dense, and so an additional impediment to launch.

Smaller scale height under high gravity, so you're out of the atmosphere quicker.

And rockets aren't the only way to get to space, as I've pointed out. Rockets are a really stupid and wasteful way to get to space, in fact. So a high-gravity civilization might bypass all that stuff and get a sensible launch system sooner.

Grant Hutchison

[Noclevername]

Rockets are a really stupid and wasteful way to get to space, in fact.

In our technology development it was the easiest to conceptualize and invent. We don't use rockets because it makes the most sense, but because we know how to build them better than most other methods.
As you said, aliens might have it different.

[Roger E. Moore]

In Hal Clement's Mission of Gravity, the Mesklinites were helped to colonize other worlds suitable for themselves, but they had to rely completely on other groups to do it.

[eburacum45]

Smaller scale height under high gravity, so you're out of the atmosphere quicker.

And rockets aren't the only way to get to space, as I've pointed out. Rockets are a really stupid and wasteful way to get to space, in fact. So a high-gravity civilization might bypass all that stuff and get a sensible launch system sooner.

Grant Hutchison

The alternatives to rockets require some really robust and reliable technology; the precise control of powerful magnetic fields for example. A simple space fountain would only get you to altitude - you'd need to accelerate to orbital speed as well (an orbital speed which would need to be much greater than around Earth).

We were ready to build orbital rockets in 1957; I don't think we could build a magnetic launch fountain even today in 2018, so it seems necessary for a hi-grav civilisation to develop more sophisticated technology in order to get into orbit than that required by a low-grav civilisation.

[selden]

Balloons are a relatively simple way to get above much of the atmosphere. Of course, like fountains, they don't provide a significant fraction of the necessary escape velocity, even when used at the equator. Some examples are described in the Wikipedia article https://en.wikipedia.org/wiki/Rockoon and https://www.theregister.co.uk/2013/0...n_test_flight/

[Roger E. Moore]

Balloons are a relatively simple way to get above much of the atmosphere. Of course, like fountains, they don't provide a significant fraction of the necessary escape velocity, even when used at the equator. Some examples are described in the Wikipedia article https://en.wikipedia.org/wiki/Rockoon and https://www.theregister.co.uk/2013/0...n_test_flight/

[slaps self] D'OH! Yes, balloons (totally forgot) would be a great way of exposing the high-grav folk to space and even giving them the rough equivalent of satellite communications coverage, weather prediction, espionage capability, and so forth, particular with tethered or maneuverable stratospheric balloons. Their "astronauts" would be balloonists--still terribly risky, but great stuff.

Wait, what was that balloon-lifted rocket program from the 1950s, which could reach extreme altitudes (hundreds of miles) but not escape velocity? That might be used, too.

[eburacum45]

I have seen a proposal for a balloon-supported launch rail, using a very large number of very large tethered balloons. If these balloons support a launch rail thousands of kilometres long, such a launch system could see spacecraft achieve a large fraction of orbital speed. It may be that some superearths might retain a non-trivial amount of helium, allowing such balloon tracks to be built more easily.

[grant hutchison]

We were ready to build orbital rockets in 1957; I don't think we could build a magnetic launch fountain even today in 2018, so it seems necessary for a hi-grav civilisation to develop more sophisticated technology in order to get into orbit than that required by a low-grav civilisation.

I'm sure that's right.
But the general principle of getting to orbit using energy provided from the ground, rather than trying to load it all aboard the vehicle, is a route high-gravity civilizations would be pushed towards. In the long term (if there is such a thing), I think our present fascination with Big F Rockets will be seen as a historical accident and wasteful sidetrack.

Grant Hutchison

[Roger E. Moore]

http://www.astronautix.com/f/farside.html

Project Farside, that was the balloon-launched rocket program I was thinking of. Suborbital, but it worked.

[Noclevername]

Suborbital isn't the issue, though.

[Roger E. Moore]

A real example of a habitable-zone super-Earth might be good.

Using the information and papers cited below, and any other science resource, speculate as to what kind of life would develop on the super-Earth LHS 1140, and what limits on technology would be placed on its intelligent inhabitants, if any.

SYNOPSIS: In 2014, a nearby red dwarf star called LHS 1140 was discovered to have a planet transiting it. Subsequent research revealed that the temperate, rocky super-Earth planet was in its star’s habitable zone for liquid water. LHS 1140 is an inactive M4.5 star only 15 parsecs away, not known to show flare activity or high UV flux. Studies also show an Earth-sized “super-Mercury” orbiting nearer to the star and hint at a possible third planet, Neptune-mass, farther out. All planets are very close to their star compared to the planets in our Solar System, and their orbits are nearly circular, relatively swift, and coplanar. None of the planets appear to be in orbital resonance with one another. The age of LHS 1140 is estimated to be over 5 billion years.

The super-Earth, LHS 1140b, has a mass currently estimated at 6.98 ± 0.98 times that of Earth, and a radius 1.727 ± 0.032 times Earth’s. Its density is ~7.5 ± 1.0 g/cm^3, with about the same ratio Earth has of iron to magnesium silicate. It is 0.0936 AU from its star on average, makes a complete orbit in 24.737 Earth days, and its orbital eccentricity is below 0.06, very circular and stable. The surface gravity is about 2.4 times Earth’s (23.7 m/s^2). Its surface area is about 3 times Earth’s. LHS 1140b receives 0.503 as much solar flux as does Earth, so the world will be on the colder side. A mild greenhouse effect in the atmosphere would warm it. As the planet is so close to its star, there is a strong possibility it is tidally locked. (The tidal acceleration placed on LHS 1140b by its star is over 100 times that borne by Earth from our Sun and Moon.) The high gravity and low stellar flux bode well for the world having an atmosphere. No moons for it have been detected yet.

Additional and more precise information may be found in the four references below. The paper by Ment et al. (2018) has the most recent planetary and stellar data; earlier papers have discrepancies caused by misjudging the distance to the star. My own calculations were used to obtain the tidal acceleration.

OPTIONS: A paper discussing the exoplanet Proxima b suggested that world might have a 3:2 spin-orbit resonance similar to that of Mercury. The tidal acceleration on Proxima b is vastly greater than that on LHS 1140b. A 3:2 rotation might boost the chances for LHS 1140b to have a significant magnetosphere from core rotation, as well as give it enormous tides. It might also rotate inclined to its orbit, giving it very fast seasons, but an inclination of near 0 degrees is more likely. If LHS 1140b has a captured 1:1 spin-orbit resonance, it is likely to be slightly ellipsoidal in shape, with its longest axis pointing through its star from the planet’s sub-solar point and center of mass.

===

https://arxiv.org/abs/1704.05556
A temperate rocky super-Earth transiting a nearby cool star
Jason A. Dittmann, et al.
Nature 544, 333 (2017)

===

https://arxiv.org/abs/1807.02483
Minimizing the bias in exoplanet detection - application to radial velocities of LHS 1140
F. Feng, et al.
Mon. Not. R. Astron. Soc. (9 July 2018)

===

https://arxiv.org/abs/1808.00485
A second planet with an Earth-like composition orbiting the nearby M dwarf LHS 1140
Kristo Ment, et al.
The Astronomical Journal, Volume 157, Issue 1, article id. 32, 13 pp. (2019)

===

http://cdsads.u-strasbg.fr/abs/2018AGUFM.P54A..03W (abstract only)
LHS 1140b: Habitable States and Observational Prospects
Wolf, E. T., et al. (12/2018)
American Geophysical Union, Fall Meeting 2018, abstract #P54A-03
LHS 1140b presents a novel case for study of a habitable zone extrasolar planet that is both larger and denser than the Earth. Initial estimates describe LHS 1140b as a cold rocky super-Earth orbiting an M-dwarf star, receiving 529 Wm-2 of stellar energy, with a planet mass of 6.62 Me and radius of 1.43 Re, yielding a bulk planet density 2.3 times greater than that of the Earth (Dittman et al. 2017). Recent revisions based on Gaia Data Release 2 (DR2; Brown et al. 2018) indicate LHS 1140b may be substantially larger and warmer, receiving 763 Wm-2 of stellar energy, with a radius of 1.72 Re, thus lowering the estimate of bulk density to perhaps 1.5 times that of the Earth (Kane 2018). While LHS 1140b clearly resides in the classical habitable zone, its size lies precariously at the transition between super-Earths and mini-Neptunian worlds (Rogers 2015). LHS 1140b has no direct analog in our Solar System, and may be either an anomalously large super-Earth or a mini-Neptune with a dense iron core. Here, using three-dimensional general circulation models appropriate for super-Earths with limited atmospheric envelopes (NCAR CAM and NASA GISS ROCKE-3D), we simulate a variety of possible planet types and atmospheres relevant for LHS 1140b, including but not limited to thick N2-H2 atmospheres, water-worlds with oceans shallow enough to have a negligible effect on planet mass, and evaporated cores. We then calculate theoretical thermal emission, reflection, and transmission spectra that may be observable with planned future space telescope missions. Our primary goals are to determine what conditions may beget habitable states for LHS 1140b, and how we may discriminate habitable states from uninhabitable states.

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https://arxiv.org/abs/1906.08783
The high-energy radiation environment of the habitable-zone super-Earth LHS 1140b
R. Spinelli, et al.
Astronomy & Astrophysics (22 June 2019)

[Roger E. Moore]

My 2 cents: Walking life won't come out of any hypothetical oceans on LHS 1140b until a much longer time passes than happened on Earth. Plants can take over the land area, but legs and hearts will be hard pressed by 2.4 Earth gravities.

Assuming that the world is tidally locked, and the oceans aren't rolling over everything because the world slowly rotates with 3:2 spin-orbit resonance.

[John Mendenhall]

Big Planet, by Jack Vance, 1952. Wiki link is here:

https://en.wikipedia.org/wiki/Big_Planet

[Roger E. Moore]

Big Planet, by Jack Vance, 1952. Wiki link is here:

https://en.wikipedia.org/wiki/Big_Planet

Never heard of it, to my astonishment. Will check it out. Thank you!

[Roger E. Moore]

Though this was about human colonization of high-gravity worlds, this thread made some good points. Trying to imagine how an alien body would adapt to these physical stresses.

https://forum.cosmoquest.org/showthr...e+high+gravity

[Roger E. Moore]

This was the article on Proxima b that suggested a 3:2 spin-orbit resonance for that world. Perhaps applicable to LHS 1140b?

https://arxiv.org/abs/1608.06813

The habitability of Proxima Centauri b. I. Irradiation, rotation and volatile inventory from formation to the present

Ignasi Ribas, et al. (Submitted on 24 Aug 2016 (v1), last revised 28 Sep 2016 (this version, v2))

Proxima b is a planet with a minimum mass of 1.3 MEarth orbiting within the habitable zone (HZ) of Proxima Centauri, a very low-mass, active star and the Sun's closest neighbor. Here we investigate a number of factors related to the potential habitability of Proxima b and its ability to maintain liquid water on its surface. We set the stage by estimating the current high-energy irradiance of the planet and show that the planet currently receives 30 times more EUV radiation than Earth and 250 times more X-rays. We compute the time evolution of the star's spectrum, which is essential for modeling the flux received over Proxima b's lifetime. We also show that Proxima b's obliquity is likely null and its spin is either synchronous or in a 3:2 spin-orbit resonance, depending on the planet's eccentricity and level of triaxiality. Next we consider the evolution of Proxima b's water inventory. We use our spectral energy distribution to compute the hydrogen loss from the planet with an improved energy-limited escape formalism. Despite the high level of stellar activity we find that Proxima b is likely to have lost less than an Earth ocean's worth of hydrogen before it reached the HZ 100-200 Myr after its formation. The largest uncertainty in our work is the initial water budget, which is not constrained by planet formation models. We conclude that Proxima b is a viable candidate habitable planet.

[Roger E. Moore]

Ants. If the planet gets a high oxygen atmoshere, insects would do great. Light and small, they'd inherit a superEarth that bigger species could not.

[Roger E. Moore]

On high gravity planets, circulatory systems have an easier time pumping sideways than upward. You could get long aliens with few tall aliens. In other words, Mesklinites.

[Roger E. Moore]

How to determine the size limits on animal and plant life on a planet with a gravity different from Earth.

===

https://www.dinox.org/sizelimit.html
Gravity Limits on the Scale of Life
by Stephen Hurrell

This is mostly about lighter-gravity limits and Earth-gravity limits.

===

https://www.smithsonianmag.com/scien...ale-180962603/

How Big Can a Land Animal Get? King Kong’s biggest enemy isn’t humans—it’s the laws of physics
By Ben Panko, smithsonian.com March 21, 2017

If you took an animal and blew it up in size, mathematics dictates that the creature's mass would increase cubically, or by a power of three. However, by the same ratio of size increase, the width of the creature's body, and thus its bones and muscles, would increase only by a power of two, says Payne. "As you get bigger you need to dedicate more and more of your body mass to your bones to support yourself," he says.

Because of these laws, taking your typical 350-pound Western gorilla and simply scaling it up by a factor of 20 would be physically impossible; the resulting creature's skeleton and muscles wouldn't be able to support its mass. Larger animals need bigger and thicker limbs to hold themselves up, says University of New Mexico paleoecologist Felisa Smith, which makes it unlikely that any creature on land has ever exceeded 100 tons. Poor King Kong couldn't even roll over," says Smith—much less attack people and helicopters.

So it's no surprise that Earth's biggest terrestrial animals—elephants—today fall far short of King Kong size. African elephants, for instance, can reach about 13 feet tall and weigh up to 7.5 tons. In the past, however, life got far larger: Dinosaurs like the Titanosaur weighed in at nearly 80 tons—10 times larger than the African elephants of today, but still nowhere near as big as the fictional King Kong.

The reason has to do with the fact that dinosaurs were reptiles, and today we live in an age dominated by mammals. To maintain their higher body temperatures, warm-blooded mammals spend about 10 times more energy than cold-blooded reptiles do on their metabolisms. This is energy that a mammal can't devote to increasing its body size. So it makes sense that the largest mammals we know of are roughly one-tenth as large as the largest reptiles ever found, Smith says.

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https://www.pnas.org/content/106/1/24.full

Two-phase increase in the maximum size of life over 3.5 billion years reflects biological innovation and environmental opportunity
Jonathan L. Payne, et al.
PNAS January 6, 2009 106 (1) 24-27

The maximum size of organisms has increased enormously since the initial appearance of life >3.5 billion years ago (Gya), but the pattern and timing of this size increase is poorly known. Consequently, controls underlying the size spectrum of the global biota have been difficult to evaluate. Our period-level compilation of the largest known fossil organisms demonstrates that maximum size increased by 16 orders of magnitude since life first appeared in the fossil record. The great majority of the increase is accounted for by 2 discrete steps of approximately equal magnitude: the first in the middle of the Paleoproterozoic Era (≈1.9 Gya) and the second during the late Neoproterozoic and early Paleozoic eras (0.6–0.45 Gya). Each size step required a major innovation in organismal complexity—first the eukaryotic cell and later eukaryotic multicellularity. These size steps coincide with, or slightly postdate, increases in the concentration of atmospheric oxygen, suggesting latent evolutionary potential was realized soon after environmental limitations were removed.

Results: The maximum body volume of organisms preserved in the fossil record has increased by ≈16 orders of magnitude over the last 3.5 billion years (Fig. 1). Increase in maximum size occurred episodically, with pronounced jumps of approximately 6 orders of magnitude in the mid-Paleoproterozoic (≈1.9 Gya) and during the Ediacaran through Ordovician (600–450 Mya). Thus, ≈75% of the overall increase in maximum body size over geological time took place during 2 geologically brief intervals that together comprise <20% of the total duration of life on Earth.

The continuing diversification of terrestrial and marine life since the Ordovician has resulted in comparatively minor increase in the sizes of the largest species. The maximum size of animals has increased by only 1.5 orders of magnitude since the Ordovician; the giant sauropods of the Mesozoic and even the extant blue whale add comparatively little to the size range of animals (Fig. 1). The largest living individual organism, the giant sequoia, is only 3 orders of magnitude bigger than the largest Ordovician cephalopod and one and a half orders of magnitude bigger than the blue whale (Fig. 1).