What if aliens can't reach Earth because gravity traps them on their worlds?

May 4, 2018, CORDIS
What if aliens can’t reach Earth because gravity traps them on their worlds?
Credit: Kateryna Kon, Shutterstock

The truth is out there. You want to believe. But you are becoming more and more frustrated because there's no conclusive evidence. All this time, the reason could be basic physics. A study submitted to the International Journal of Astrobiology suggests that aliens living on distant planets can't cruise the cosmos because of gravity.

Man has found numerous exoplanets in the hunt for . Most are large planets like Jupiter, while some are the size of Earth or slightly smaller. Others fall somewhere in between and are called super-Earths. They're about 10 times larger than Earth.

If aliens are out there, why are they grounded?

Astronomers and astrophysicists believe that super-Earths could shelter . If earthlings can build rockets and explore the universe, why can't extraterrestrials do the same? According to the findings, super-Earths have massive gravitational pulls. These keep alien spacecraft from generating enough thrust to escape the gravitational forces of their home planets. To launch the equivalent of an Apollo moon mission, a rocket on a super-Earth would need to have a mass of about 440 000 tonnes because of fuel requirements.

"On more-massive planets, spaceflight would be exponentially more expensive," study author Michael Hippke, an independent researcher affiliated with the Sonneberg Observatory in Germany, told Space.com. "Such civilizations would not have satellite TV, a or a Hubble Space Telescope."

Hippke examined how difficult it would be to blast off from a hypothetical super-Earth. He calculated the sizes needed to escape a super-Earth that is 70 % wider than our planet and 10 times more massive. These are about the dimensions of the planet Kepler-20b, which lies some 950 light years from Earth. On this super-Earth, the escape velocity needed would be roughly 2.4 times greater than on our planet.

Speaking to the UK's 'Daily Mail', Hippke said: "Civilisations from super-Earths are much less likely to explore the stars. Instead, they would be to some extent arrested on their home planet and, for example, make more use of lasers or radio telescopes for interstellar communication instead of sending probes or spaceships."

Fuel – the great barrier to alien travel

The weight of the fuel that conventional rockets carry is another major challenge for aliens on a planet like Kepler-20b. This means that they would need to use rockets that don't depend on chemical fuel to get into space. According to the research, a potential solution is a nuclear-powered spacecraft to leave a planet more than 10 times Earth's mass.

But they're extraterrestrials, after all! Shouldn't they have some kind of alien technology to help them get off their ? Until then, some of us will have a good excuse as to why we haven't seen UFOs cruising overhead.

Explore further: The challenges of an alien spaceflight program—escaping super-Earths and red dwarf stars

More information: Spaceflight from Super-Earths is difficult: arXiv:1804.04727 [physics.pop-ph] arxiv.org/abs/1804.04727

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Lischyn
4.5 / 5 (6) May 04, 2018
Dumb write-up. The author assumes using only rocket power. There is probably more efficient methods to get off the ground. We just haven't discovered them. Rockets are probably the worst. We need to understand the structure of space-time and gravity. Then we can build something more intelligent than rockets.
antialias_physorg
3 / 5 (7) May 04, 2018
Yah..it's a really pointless piece of fluff. All conjecture and no kind of data instead of 'gravity is hard'. Well, yeah.

They could use railguns to launch stuff into orbit (including fuel that is then used there for further propulsion). They could use nuclear propulsion.
Eikka
4.8 / 5 (4) May 04, 2018

They could use railguns to launch stuff into orbit (including fuel that is then used there for further propulsion). They could use nuclear propulsion.


Don't forget that higher gravity also means denser atmosphere, so it's much harder to accelerate stuff to escape velocities while you're in it. That goes for all sorts of flying machines as well, because of the air drag.

There's all sorts of issues with high gravity. An ordinary bicycle wouldn't hold a person weighing 750 kg, so transportation is an issue. Combustion becomes explosions because of the high pressure environment, so keeping a fire is hazardous business. Engines don't work very well either.

You can't even have buildings, because common materials like steel become play-doh when you increase the load 10x.

In fact it's very hard to imagine any sort of technological civilization existing at all on a planet with 10x earth's gravity.
JeffHargrove
3 / 5 (2) May 04, 2018
Gravity depends on two things. Mass of the objects affected, and distance between them. They are making a significant amount of assumptions in this article. First they are assuming that the star is of similar mass to our own. Considering ours is a yellow Dwarf star, and only 10% of stars are yellow dwarfs that is a big assumption.

Second they are assuming that an increase of 10x volume of a planet would correlate to an increase of 10x mass. Without even giving consideration to density of the planet.

Third similar assumptions on moon. Some moon to planet ratio's of mass density and volume could greatly affect space travel. Our moon can lower rocket fuel costs by 1% flying into it, but in some situation it could lower cost by much much more.

This fictional planet they are speaking of in this article would literally be like finding a specific needle in a stack of needles.
Mark Thomas
5 / 5 (3) May 04, 2018
Not a dumb write-up. In a universe as large as this one, every impediment to reaching space could prove to be critical for someone. It may turn out that a fair number of civilizations destroy themselves before they are able to establish a presence outside their home worlds, even though they could have done so if they tried. We may be one of those civilizations, but my gut tells me we aren't.

IMHO, our exploration of space is clearly slowed because it is so far removed from the everyday experiences of the voters. Increasing the cost of reaching orbit only makes matters worse. Perhaps even more importantly, it is not hard to image a similar civilization on a perpetually hazy or cloudy exoplanet where the "people" there would be even less likely to support space exploration because nobody had ever seen anything in space with their own "eyes." I think it likely this period of emergence into space is a critical juncture separating many of those who make it from those who don't.
alexander2468
3 / 5 (2) May 04, 2018
As daft as a brush question
If aliens are out there, why are they grounded?
The same reason we are grounded; we have no propulsion unit!

What everyone has to be searching their soul for is why is no one interested in making a space propulsion units, rockets have shown the potential in space now we have to get serious or we might never see the moon again certainly not the planets.
Suriv9
5 / 5 (2) May 04, 2018
Soooo it's not the vast stretches of space and time that stop it... the mere scale of travelling through an entire universe... but simply overcoming basic gravity. If you're going to force me to take the leap and imagine that aliens can overcome the distance and time issue.. then certainly gravity is small in comparison...
ShotmanMaslo
4 / 5 (4) May 04, 2018

There's all sorts of issues with high gravity. An ordinary bicycle wouldn't hold a person weighing 750 kg, so transportation is an issue.
You can't even have buildings, because common materials like steel become play-doh when you increase the load 10x.
In fact it's very hard to imagine any sort of technological civilization existing at all on a planet with 10x earth's gravity.


You need to take into account not just mass of the planet, but also increased radius. Super-Earths only have around three times the surface gravity of Earth.

https://en.wikipe...er-Earth
Mark Thomas
4.7 / 5 (3) May 04, 2018
Suriv9, I would agree that the vast distances certainly appear to be a far greater problem than the depth of your gravity well. However, who knows how we will view this in the distant future. Maybe travel through interstellar space is actually relatively easy once your technology reaches a certain level, but deciding to invest a lot of time and effort to explore space at the beginning is the real trick. Let's face it, we got lucky with the space race to the moon, but even with that achievement to show us what is possible, nobody has even tried to get beyond LEO since 1972.
Eikka
3.7 / 5 (3) May 04, 2018
Super-Earths only have around three times the surface gravity of Earth.


Yet:

The new research suggests that the rocky centres of super-Earths are unlikely to evolve into terrestrial rocky planets like the inner planets of the Solar System because they appear to hold on to their large atmospheres. Rather than evolving to a planet composed mainly of rock with a thin atmosphere, the small rocky core remains engulfed by its large hydrogen-rich envelope


The higher gravity means the planet has to be closer to its host star to lose the dense atmosphere by radiation pressure, but that also means it's going to be entirely too hostile for life. Hence, if the planet is much heavier than Earth, it's unlikely there's going to be anything alive in there to begin with.
snoosebaum
not rated yet May 04, 2018
and why would only super earths have life ?
Ensa
3 / 5 (4) May 04, 2018
There is no reason to assume aliens would not use nuclear. The only reason we don't is political.
humy
3 / 5 (2) May 04, 2018
As a more practical alternative to rockets, they could use what is called "beam-power propulsion" to get payloads into space despite the high gravity. They would have to be all pretty stupid for litrally none of them to ever come up with this idea.
See;

https://en.wikipe...opulsion
evercurious
not rated yet May 04, 2018
It may also come back down to phosphorous. With such mass, the landscape would be even smoother than Earth's is. Metals might be drawn further into the core. The distribution of minerals we have is oddly essential to OUR way of life.

If water could form on the surface, it might be uniform. Under such weight, I couldn't imagine anything with a skeleton, internal or external. Life outside of any body of water would have to be smaller in structure. On earth, an ant can survive falling off of a building. On such a world, even with a denser atmosphere, a fall even for a small creature might almost always be lethal.

It's pretty hard on Earth to create a radio tower. A massive planet would make the construction almost impossible but, probably unnecessary. A smoother landscape would allow for easier communication and probably lead to a monoculture. Without genetic diversity, we've seen monocultures fail dramatically on earth - with genetically identical bananas going nearly extinct.
JamesG
1.6 / 5 (7) May 04, 2018
Sorry but give it up people. There are no aliens. There are a lot of hoaxes but there are no aliens. Movies will have to do.
Mimath224
5 / 5 (2) May 04, 2018
Not a dumb write-up. In a universe as large as this one, every impediment to reaching space could prove to be critical for someone. It may turn out that a fair number of civilizations destroy themselves before they are able to establish a presence outside their home worlds, even though they could have done so if they tried. We may be one of those civilizations, but my gut tells...


Yes, I also wonder if muscular development would progress similar to ours. If it doesn't then alien life might be more squat than we are and have more difficulty in moving around. A 'body builder' there might have have the equivalent strength of a weak person here. Alternatively, of course, they may be very muscular and might dwarf a 'mister universe' here. Although astronauts take part in the effects of micro gravity on brain function I don't think experiments have yet been performed to look at brain development (in animals) from birth. We need more time to answer these questions.
Eikka
not rated yet May 05, 2018
"beam-power propulsion" to get payloads into space despite the high gravity. They would have to be all pretty stupid for litrally none of them to ever come up with this idea.


Notice also that this idea doesn't actually work. Nobody's managed to actually "beam" anything to orbit - it takes enormous amount of power even under Earth gravity, and such high power densities are likely to just evaporate the spacecraft.

Takes about 1 MW per kg to get stuff up there, theoretically, so a spacecraft weighing one ton would need a gigawatt, etc.
granville583762
2.7 / 5 (7) May 05, 2018
You do not need to achieve orbital velocity

You have to apply Newton's laws of motion and gravity; gravity is simply acceleration in combination with mass is a force, all you have to do is match the force of your on your space vehicle with the mass x acceleration and your weightless, 1N greater and you continue to accelerate upwards. No one said we have to reach orbital velocity; you can go as far as you like accelerating with a force + 1N
granville583762
3 / 5 (6) May 05, 2018
Acceleration does not need to continuous

Energy is force x distance or F(at*/2) where v=at so it clear from Newton's laws the energy required depends on the duration of each step of acceleration because the velocity is a multiplicative of each step where the energy is a multiplicative of each step of acceleration. Sir Isaac Newton must be looking down in dismay at every one, now we have the industrial capacity to put his formulas into operation, where instead we're using 1000 year old Chinese rockets.
antialias_physorg
3.7 / 5 (6) May 05, 2018
You do not need to achieve orbital velocity

Achieving orbital velocity is a lot easier than getting into deep space as a means of getting something 'off planet' (and having it stay there).
https://what-if.xkcd.com/58/
(see third cartoon)

Getting up into space is not a problem. *Staying* up is. If you shoot a rocket straight up it will just fall back gown. That's why you see rockets curve horizontally soon after lift off. What all that fuel is for is to achieve velocity *sideways* so you *stay* in orbit once you get there. Only a part is used to actually travel up.

Orbital velocity goes with the square root of the mass of the planet. So the effort for aliens on a planet twice as massive as Earth would be1.4 times as high as for us. If their planet has a bigger radius than ours it actually gets easier because orbital velocity also goes by 1 over the square root of the distance to the center.
http://www.softsc...mula/76/
antialias_physorg
3 / 5 (4) May 05, 2018
Once you achieve orbit you're "home free", though. Because nothing stops you from setting up a fuel depot in orbit and continually launching fuel shuttles there until you have enough to power a craft that can escape the gravity well of your world altogether.

To get the fuel you need to achieve a certain speed you use the Tsiolkovski formula
https://en.wikipe...equation
From this it is easy to see that orbit is a lot more accessible than straight up going into deep space.
granville583762
5 / 5 (3) May 05, 2018
Motion without wheels - The mass to produce the force to propel the space vehicle
antialias_physorg > Once you achieve orbit you're "home free", though. Because nothing stops you from setting up a fuel depot in orbit and continually launching fuel shuttles there until you have enough to power a craft that can escape the gravity well of your world altogether.

That is why the energy required depends on the duration of each step of acceleration, because the velocity is a multiplicative of each step where the energy is a multiplicative of each step of acceleration.

The smaller the distance you accelerate the mass to produce the force, the energy required to accelerate the mass is proportional to the time squared divided by the number of steps in a second, as the mass that I am discussing is not the space vehicles mass, but the mass to produce the force to propel the space vehicle.
granville583762
5 / 5 (3) May 05, 2018
Newton's law of reaction works equally angularly and linearly

It is not written in tablets of stone the mass to produce the force is expelled only linearly, all matter in space spins about their moment of inertia, Newton's law of reaction works equally angularly and linearly separately or in a combination of both
humy
5 / 5 (1) May 05, 2018
"beam-power propulsion" to get payloads into space despite the high gravity. They would have to be all pretty stupid for litrally none of them to ever come up with this idea.


Notice also that this idea doesn't actually work.

Eikka

In what sense "Notice" it doesn't work?
Nobody yet has tried to make something go all the way to outer space that way because the technology has yet to be developed to do that thus it certainly has NOT been shown not to work and thus you are talking total crap.

Nobody's managed to actually "beam" anything to orbit

"beam-power propulsion" doesn't mean "beam" something to orbit.
And the only reason why nobody has managed to get something up there that way is because the technology to do so has yet to be developed.
Using your same stupid 'logic', if you were at the time before rocket technology had been developed for going into outer space, you would have said it must be impossible to ever put a rocket into orbit.

eachus
not rated yet May 05, 2018
First, if a super-Earth has a day similar to that of Earth, you would get 3 times the advantage by launching toward the East from the equator. Arianespace SA launches from French Guiana only 5 degrees from the equator, which gets most of the advantage. On a super-Earth, wasting any of that advantage might make a mission impossible. The length a space elevator is determined not by gravitational strength but purely by rotational dynamics. (A space elevator on a super-Earth would not need to be any longer than on Earth, if the days were the same length.) The taper ratio--size of the elevator strands at equatorial orbit divided by that at the surface--would not be as good, which would make for a heavier elevator. But we now have materials with taper ratios under two for Earth (carbon nanotubes), and materials with even smaller tapers are under consideration.

So our hypothetical aliens could use a Nerva style nuclear rocket to put up a SE or perhaps tethers instead.
granville583762
5 / 5 (3) May 05, 2018
The rocket community
antialias_physorg:- Tsiolkovsky rocket equation describes the motion of vehicles that follow the basic principle of a rocket applying acceleration to its self using thrust by expelling part of its mass
The mass it ejects out into space has to be accelerated where its momentum is lost with the mass as it disappears into the distance, the total distance you can travel in space is limited by the capacity of disposable mass. a rocket with a nuclear reactor to accelerate the mass, where your nuclear reactor will continue providing energy for decades you still have to carry decades of mass the rocket will only be disposable mass there will be no room for the occupants. We have become the rocket community and consequently we are grounded on planet earth, are last venture from planet earth is the Moon Apollo 11 landing on July 20 1969, that is 49 years since walking on the moon exemplifies the inadequacies of rocket propellant propulsion.
Edenlegaia
not rated yet May 05, 2018
What if aliens loves to break laws? We discovered things we decided are definitive and can hardly change.
We can imagine those poor guys being stuck on theirs rocks. We can also imagine them doing things waaaaaay differently.
Let's not make those aliens too "humans" in our heads. We didn't meet them yet. How could we know what they did or didn't?
doogsnova
2 / 5 (4) May 05, 2018
THERE IS CONCLUSIVE EVIDENCE. Former top air force OSI investigator concludes Meier case is real. Lt. Col. Wendelle Stevens concluded Meier case is real. Harry Lear (Pentagon and Saigon, Vietnam MACV HQ in SSD, ACSI, Special Security Detachment, Assistant Chief of Staff Intelligence, Top Secret Crypto EO NOFORN, other classified special access codes – 1965-67 US Army concludes Meier evidence is authentic. 1476 photos, 125 eye the, 200 published discoveries before anyone in the scientific world, 34 films, footprints, metal samples, sound recordings, all analyzed and tested by the world's top experts concludes the evidence is real. You are either a liar, an idiot, or a paid cover up shill. https://youtu.be/8o8YdpFki7g
doogsnova
2 / 5 (4) May 05, 2018
125 eye witnesses I mean to say. 17 of which took and voice stress analysis lie detector tests and passed. Multiple photographers. At least 6 people have seen them in the flesh in this still ongoing case of visitation.
GaryB
5 / 5 (1) May 06, 2018
Bigger earth, thicker atmosphere, higher flights with winged craft or balloons -- take off from 200 miles up.
Doug_Nightmare
5 / 5 (1) May 06, 2018
"If earthlings can ... explore the universe ..."

Fine premise ignored. We cannot explore the universe.
humy
1 / 5 (1) May 06, 2018
"If earthlings can ... explore the universe ..."

Fine premise ignored. We cannot explore the universe.

Unless we find a practical way to break the light barrier which I think is very unlikely, true.
If a practical way to break the light barrier is possible and there are intelligent aliens then I see no credible reason why we wouldn't be both visited by aliens and very clearly all know we have and from a long time ago.
Eikka
not rated yet May 06, 2018
Nobody yet has tried to make something go all the way to outer space that way because the technology has yet to be developed to do that thus it certainly has NOT been shown not to work and thus you are talking total crap.


That's exactly what I'm talking about. It's not been shown to work, so trying to appeal to "they could be using beam propulsion" is just plain crap. It's stacking what ifs on wishful thinking, applied to imaginary aliens.

"beam-power propulsion" doesn't mean "beam" something to orbit.

That was simply shorthand.

And the only reason why nobody has managed to get something up there that way is because the technology to do so has yet to be developed.


Exactly. Though it's been tried.

you would have said it must be impossible to ever put a rocket into orbit.


The difference here is that the power requirements - as proven by experiments - show that it's practically impossible for anything but small microsatellites.
Eikka
not rated yet May 06, 2018
Using your same stupid 'logic',


Using my "stupid" logic to look up the power requirements form the wikipedia article you provided, at 1 MW per kg of payload to orbit, it's immensely expensive to launch anything remotely massive.

A spacecraft that can carry a single person is going to weigh tons, so you'd actually need a significant portion of the entire electricity generation capacity of the USA to launch one. Getting that amount of power rapidly, controllably, isn't possible except by some sort of chemical reaction.

So what you're actually talking about is building a multi-gigawatt chemical laser, and then strapping a person in a capsule that's going to be shot with said laser until it reaches orbit - and hoping the whole thing doesn't evaporate along the way.

At least with rocket propulsion, you could show by calculation that the energy density of the fuel is enough to get you up there. The rest was about finding a good fuel combination.
Eikka
not rated yet May 06, 2018
You can read the book "Ignition!" by John D Clark for a bit of history on rocket fuels and what sort of crazy chemicals they tried to come up with the rocket fuels we use today.

antialias_physorg
3 / 5 (2) May 06, 2018
Unless we find a practical way to break the light barrier which I think is very unlikely, true.

I think what most people don't realize is that the speed of light isn't just some arbitraty speed that photons (or generally masless particles) run on but it is the actual speed limit of information. That is, if one could break that limit then we'd run into all kinds of problems with paradoxes. So if we posit the universe to be paradox-free then speed of light it is - and no more.*

*This does not account for ways to circumvent speed of light like the Alcubierre drive in which nothing actually moves faster than c.
Mark Thomas
1 / 5 (2) May 06, 2018
This does not account for ways to circumvent speed of light like the Alcubierre drive in which nothing actually moves faster than c.


Exactly. So let's be completely honest here. If someday we find a way to build the USS Enterprise, explorers won't care much whether we did it by breaking the law that says it is impossible to travel faster than c, or we did it by simply by circumventing that law. The net effect is the same.

Also consider that none of us would be alive if it weren't for at least one process that happens FTL. Life on Earth depends on energy from the Sun, energy from the Sun depends on fusion, fusion depends on quantum mechanical tunneling, quantum mechanical tunneling happens much faster than c.

The universe we see is a result of cosmic inflation, another FTL process. The collapse of quantum mechanical entanglement is FTL too. Seems like the law is circumvented all the time.
antialias_physorg
1 / 5 (1) May 06, 2018
If someday we find a way to build the USS Enterprise, explorers won't care much whether we did it by breaking the law that says it is impossible to travel faster than c,

It doesn't matter how one translocates. But - and I feel this is important - an Alcubierre type drive does not break any law (including the speed-of-light limit). Aliens don't get to pick and choose the physiscs they want to adhere to any more than we do.

quantum mechanical tunneling happens much faster than c.

But it doesn't contradict special relativity (or the speed of information speed limit). It#s a bit like 'spooky action at a distance' - which can happen over any kind of distance instantaneously but does not convey information (which means it cannot be used for message transmission - much less travel)
humy
1 / 5 (2) May 06, 2018

The difference here is that the power requirements - as proven by experiments - show that it's practically impossible for anything but small microsatellites.

Eikka

Please don't lie. No such experiment showed it to be impossible.
You have also failed to explain why it would be impossible; Making up crap up about "power requirement" instead when the power requirement for this would be less than that for rockets. You are obviously talking nonsense.
andyf
5 / 5 (2) May 06, 2018
The nutters are intent on destroying each other tonight.
Mark Thomas
not rated yet May 06, 2018
an Alcubierre type drive does not break any law (including the speed-of-light limit).


Yes, that is my understanding as well, assuming we can generate enough negative energy anyway.

I am NOT necessarily trying to argue Einstein was wrong, my point is that there appear to be multiple ways to circumvent the limits concerning c. A colonist won't care that Einstein will still be considered technically correct if an FTL drive enables them to reach Alpha Centauri in 1 year, not including time dilation.

We haven't even discussed wormholes yet. :-)
doogsnova
2 / 5 (3) May 06, 2018
Sorry but give it up people. There are no aliens. There are a lot of hoaxes but there are no aliens. Movies will have to do.


Sorry, James. You haven't found the evidence. 1,476 photos. 34 films. Metal samples. Sound recordings. Fingerprints. Footprints. Multiple photographers. 125 eye witnesses. 705 contact report transcripts. 200 corroborations in print before they were "discovered". Just because you haven't done the research, doesn't mean the proof isn't out there. You don't want to find the evidence.
Mark Thomas
1 / 5 (1) May 06, 2018
There are no aliens


We are all aliens.

Earth is wonderful, but there must be similar planets out there. Since life arose here, you can bet it arose somewhere else. Who is to say which race is alien or not, so in effect, we ARE aliens too. As a matter of probability, they are almost certainly out there. The only question is whether they are 4 light years away or 4 billion light years away. My money is on a distance between those two extremes.
Mimath224
3 / 5 (2) May 07, 2018
Sorry but give it up people. There are no aliens. There are a lot of hoaxes but there are no aliens. Movies will have to do.


Sorry, James. You haven't found the evidence. 1,476 photos. 34 films. Metal samples. Sound recording...Just because you haven't done the research, doesn't mean the proof isn't out there. You don't want to find the evidence.

As I posted on related threads, I was, years ago, a very active investigator into strange phenomena, UFO's in particular. As much as 90% of 'general public' reports were mis-identification (Venus) and were all generally uninteresting. But there always remained those that were hard to explain, if at all. My favourites were Vehicle Interference and I did a several year study and personally investigated many of them (with technicians of various disciplines). Gears, engine parts etc would be found affected in various ways. There were many hoaxes which gave the subject a bad name but something we had to live with.
Eikka
5 / 5 (2) May 07, 2018
Please don't lie. No such experiment showed it to be impossible.


The wiki article points out the power requirements derived by experiment. Launching a 10 ton mass to LEO using beam propulsion takes about 10 GW.

You have also failed to explain why it would be impossible;


I already did: the power requirements are too enormous to handle.

Making up crap up about "power requirement" instead when the power requirement for this would be less than that for rockets. You are obviously talking nonsense.

Different practical constraints apply in powering lasers than in powering chemical rockets.

Launching heavier objects quickly increases the beam power (power density) to ridiculous numbers, because the mass of the craft increases by its volume which grows faster (r^3) than the area of the target (r^2), so you need 99.9999999% efficient mirrors or your spacecraft itself will turn to plasma, since it's being shot with a literal death ray.
Eikka
4 / 5 (4) May 07, 2018
The first practical issue is, where are you going to get 10 GW of (electrical?) power at the flip of a switch, and then turn it off again two minutes later? If you're running a chemical laser, the whole argument about it being cheap (just dollars worth of electricity) flies out the window.

The second practical issue is, beam propulsion doesn't actually have much different thrust-to-weight ratio to chemical rockets, because it still needs reaction mass to shoot out the back - only the power source is externalized: the laser/microwave heats up the inert propellant in the rocket which is exhausted through a rocket nozzle. The main advantage is with the lower stage where the atmosphere can be used as reaction mass, so you get a "free" first stage, giving you lower launch costs.

But with similiar thrust-to-weight ratios, how is this going to help on a planet with higher gravity, where ordinary rockets can't get up?
granville583762
5 / 5 (3) May 07, 2018
What are our Alternatives to obsolete rockets

Chemical reaction inertial propulsion engines have only achieved a manned landing o the moon 50 years ago, with non planned in the near future; can any calculate the mass and size of the launch rocket required for that endeavour, that planet was in earth's orbit. Rockets have shown they cannot take us out of earth's orbit to manned landings on our solar system planets
humy
2.3 / 5 (3) May 07, 2018
Please don't lie. No such experiment showed it to be impossible.


The wiki article points out the power requirements derived by experiment. Launching a 10 ton mass to LEO using beam propulsion takes about 10 GW.

Eikka

So what? How does that show getting something in orbit using beam power propulsion will always be impossible as you claimed?

You have also failed to explain why it would be impossible;

I already did: the power requirements are too enormous to handle.

In what way are the "power requirements are too enormous to handle"? Please don't make up crap.


Launching heavier objects quickly increases the beam power (power density) to ridiculous numbers, because the mass of the craft increases by its volume which grows faster (r^3) than the area of the target (r^2),

Its volume is irrelevant. Its mass is what's relevant. Thus you make no sense.

humy
3 / 5 (4) May 07, 2018
so you need 99.9999999% efficient mirrors or your spacecraft itself will turn to plasma,

Why would all types of beem power propulsion require "mirrors"? Not all types would. What about those that don't require mirrors? Why would they be "impossible" as you cleam? Also, some of those that do have mirrors have already been demonstrated to be able to accelerate up at the required acceleration (but not all the way up to space, obviously) just fine without turning "to plasma". You are talking made up crap yet again.
gnappi
1 / 5 (4) May 07, 2018
"Until then, some of us will have a good excuse as to why we haven't seen UFOs cruising overhead. "
Really? Google it: yahoo operation saucer the official search for ufos 155317526
antialias_physorg
3.4 / 5 (5) May 07, 2018
You haven't found the evidence. 1,476 photos. 34 films. Metal samples. Sound recordings. Fingerprints. Footprints. Multiple photographers. 125 eye witnesses. 705 contact report transcripts. 200 corroborations in print before they were "discovered".

To be fair: There are any number witnesses and material objects that say there are gods (down to burnt images of his son on toast) - but that still doesn't learn any smidgeon of credence to the notion that there are any.
granville583762
5 / 5 (3) May 07, 2018
We need some of this inner space Astronomers and astrophysicists inhabit!

If earthlings can build rockets and explore the universe, why can't extraterrestrials do the same?

Not even our in our dreams, unless he thinks visting the moon 49 years ago counts as a trip to our nieghbours in the Andromeda galaxy.
Mimath224
not rated yet May 07, 2018
You haven't found the evidence. 1,476 photos. 34 films. Metal samples..".

To be fair: There are any number witnesses and material objects that say...

@antialias_physorg. Oh Come on, that's hardly 'fair' as you put it. Ideas concerning the existence of aliens, UFO's are not mythical or religious even if ancient people viewed alleged visits as being so. The phenomena is a physical one and needs to be addressed as such. The real problem is 'there ain't no profit in it' and our society is money/profit based. The present private space race is about who can get to 'up there' first to start mining and they have made no secret of it, 'Planetary Resources that estimated that a football field-size asteroid could contain up to $50 billion worth of platinum...Wash.Post Apr.2017' to quote just one source. These people don't care about about the possibility of life out there as long as there is Gold, diamonds etc.
Da Schneib
1 / 5 (1) May 08, 2018
The main advantage is with the lower stage where the atmosphere can be used as reaction mass, so you get a "free" first stage, giving you lower launch costs.
It's going to be a pretty major advantage considering that's where the most fuel and most cost is.

But with similiar thrust-to-weight ratios, how is this going to help on a planet with higher gravity, where ordinary rockets can't get up?
Atmospheric density is going to be higher at the surface. That means beam propulsion is going to give a better thrust-to-weight ratio, just at the time where it's most needed. I'm surprised, @Eikka, that you can't see the math for this. The weight that is the most costly, that at launch from the surface, is the very weight that beam launch provides the most advantage with in the lower atmosphere. @humy's idea may actually be better than @humy realized; it may be easier to launch things by beam launch from super-Earths.
Da Schneib
3 / 5 (4) May 08, 2018
@Mimath, but @anti's point isn't about religion. It's about conspiracy theories of all types, religion included.

Having duplicated photographs with "flying saucers" in them when I received prints of photos I had taken with a Kodak "camera in a box" at the Petrified Forest on vacation, when the film transport malfunctioned, and the film was bent inside the camera, I stopped giving credence to UFO "pictures" decades ago. I *remember* taking those pictures, and there was nothing there. I remember my wife commenting on what was a good shot, and commenting back that the camera was malfunctioning. I switched to another one (I had figured they might be unreliable-- "camera in a box" after all-- and had spares) and got some good shots. So don't BS me about "flying saucers."
Mimath224
3 / 5 (2) May 08, 2018
Da Schneib, No I am not with you on this one. I am versed in conspiracy theories and I agree that UFO's fall into that category. But antialias_physorg DID say '...gods (down to burnt images of his son on toast)...' and that is clearly a religious or mythical reference.
There is no need to use derogatory expletives, 'BS', it is quite unnecessary especially as I never use same with you or any other poster. You know I am not a troll. And I never mentioned 'flying saucers' I wrote 'UFO', they are NOT one and the same. The term 'flying saucer' was used by the media when referring K. Arnold's sighting. EVEN HE didn't call the objects by that term. The drawing he made is not even circular in shape.
Please keep the discussion genuine & objective (as I have done on other threads with you where my knowledge has been lacking) and we can move forward. Thank you
antialias_physorg
4.2 / 5 (5) May 08, 2018
Oh Come on, that's hardly 'fair' as you put it. Ideas concerning the existence of aliens, UFO's are not mythical or religious

What I'm saying is that all the evidence for UFOs/aliens has the same issue that evidence for religions has: it's not testable/verifiable. (No, I was not targetting religions per se...they are just the most universally known example of this kind of 'evidence'. I could have gone with an example about "evidence for a Wolpertinger" but since I don't know where you're from I have no idea whether you - or anyone else - would know what I'm referring to.)

While I don't think we're alone in this universe (just from a probability perspective that would be pretty amazing) I'm also not convinced aliens who can traverse interstellar distances are the kind of stupid that would leave the kind of evidence that is claimed to exist. There's a strange disconnect required here between 'highly developed' and at the same time 'utterly incompetent' that I'm not buying.
Mimath224
3 / 5 (2) May 08, 2018
@antialias_physorg I appreciate your reply and yes, I understand what you're saying. I can tell you now, you don't the 'half of it' as far as ridiculous claims. When I sat down to interview a witness once after being told of a 'fantastic encounter' I left feeling...disappointed &..
"...then I saw it land in a field. I stopped the car and went...the aliens told me they were from Rigel [Beta Orionis]..." antialias_physorg, I left teeth marks on my lips and my two companions had to excuse themselves, I wonder why (Ha!)? If that had been my first interview it might have been my last too. At the other extreme, my team and I interviewed a pilot who had been scared
by a 'UFO' whizzing by the aircraft he piloting and all he saw was a number of revolving red lights that faded in the distance...it turned out to be a practice Blood Hound missile fired outside of military regulation time. The 'red lights' would have been the red hot tail fins. (cont.)
Mimath224
1 / 5 (1) May 08, 2018
(cont.) However, here's a youtube video of a recent US Military release of an event that happened a few year ago. (there are various clips so you might want to view others as the quality and video length varies. type in your search engine 'Pentagon releases video of Navy jets chasing UFO | The Times of ...' or similar on youtube. The Navy Jets were on a training mission in 2004, Mach <1 @ 25000 ft. . Without examining the original it would be difficult to make any real appraisal. The object appears circular most of the time but not at the end. This is the Pilots opinion on; https://abcnews.g...1856514; These F/A 18F jets have a max speed of under mach 2 at 40,000ft. I'm not suggesting it as proof of anything but would just like to hear your opinion having heard others. (cont)
Mimath224
1 / 5 (1) May 08, 2018
(cont) To be fair (ha!) the US military has said there are 3 possibilities; 1 equipment malfunction of natural phenomena, 2 test flight of secret military aircraft & 3 Alien origin. But in recent years, in various countries, jets have apparently been scrambled to intercept craft that have either outrun the jets, out-maneuvering the jets (turning at seemly impossible angles) or simply 'vanishing'.
Yes, I will agree that this doesn't mean that they are of alien origin BUT if someone on Earth really has that kind of technology why bother spending billions on rockets, faster, better stealth type etc. the economics alone need to be questioned. I hope they put a family model on the market...imagine the 'one-upmanship' on the neighbors (ha!).

antialias_physorg
3.5 / 5 (4) May 08, 2018
I'm with Neil deGrasse Tyson on this one: when you call something a *U*FO and "of alien origin" in the same sentence then you're contradicting yourself.
https://www.youtu...YRGbsMW0
Mimath224
1 / 5 (1) May 08, 2018
@antialias_physorg
I'm with Neil deGrasse Tyson on this one: when you call something a *U*FO and "of alien origin" in the same sentence then you're contradicting yourself.
https://www.youtu...YRGbsMW0

I don't think I'm guilty of that. I have always respected what 'unidentified' means. In fact there are other categories within this that many don't know of, and they all start with 'U'. Unless one has worked in this field one is ignorant of it's complexity and just how much genuine effort is employed. Most people only read the sensationalist reports by the media...it's great way to boost sales of the tabloids. Don't misunderstand me. What the phenomena needs is scientist like Neil deGrasse Tyson to get involved and I mean really involved, and I for one would welcome it. But only a few have and there a several reasons. They have to earn a living just like the rest of us and can hardly spend many hours interviewing & checking this and that. (cont.)
Zzzzzzzz
not rated yet May 08, 2018
Turn this around. Why haven't we visited them? Are we trapped by our planet's gravity? Are we trapped by our having evolved in a certain type of environment, and our inability to exist much outside that environment? Are we trapped by our short lifespans, and/or how they compare to the vast distances involved? Just why the hell aren't WE "cruising the cosmos"?

To suppose that only that the gravity of a "super earth" could stop the "cosmic cruising" is really quite stupid. I wonder if the dimwits involved were brave enough to sign their "study".....
Zzzzzzzz
not rated yet May 08, 2018
humy, evidently you weren't aware that Eikka knows everything, and is an expert in every subject you can dream of.
Mimath224
not rated yet May 08, 2018
(cont.) Others are duty bound by grants or company policies and stepping outside of those
could have repercussions. And, of course, some are not interested. So who is left? And if you
are of the opinion that there is NO phenomena to investigate then it would be denying much.
I am not suggesting that scientist should desist from studying the universe in preference to the
phenomena, not at all. For it is that very knowledge that will help us understand what does &
doesn't exist, what can & can't exist. (cont.)
Mimath224
1 / 5 (1) May 08, 2018
(cont.)So it's left to people like me, in search of the truth and if
during that search we come up with something that is a mystery or seems impossible we get
criticized by the very community that refuses to help (for the reasons stated). It's a no win
situation. But to some of us truth is more important and worth the effort. Neil deGrasse Tyson
might say that 'u' doesn't mean alien but until his type get off the soap box and DO SOMETHING ABOUT IT, it remains a criticism of people who try.
antialias_physorg
3.4 / 5 (5) May 09, 2018
What the phenomena needs is scientist like Neil deGrasse Tyson to get involved and I mean really involved

So what do you think their involvement changes? The evidence doesn't become any more testable/verifiable by their involvement. Scientists don't just wave a magic want and something becomes 'scientific'. Scientists employ the scientific method. And that just doesn't work on something that doesn't show up in the lab but only on fuzzy video.

Others are duty bound by grants or company policies and stepping outside of those
could have repercussions.

No, what you do in your spare time is your business - even in science. Grants and such don't beholden you to anyone (they are *grants*. Once granted they can't be revoked unless your reports show you're not using the money for the subject you got the grant for. If you use the grant money given for investigating the efficiency of dishwashers on UFO research you'll get into trouble, tho. ).
antialias_physorg
3.4 / 5 (5) May 09, 2018
Of course you are free to collect money on kickstarter, or similar, and then use that money as grant money for scientists to investigate any kind of evidence you feel you have. But I can guarantee you that you won't get any better results than some random dude staring at the vids. Scientists aren't magicians.
"Yes it's a blob. Yes it appears to move in a manner that no airplane can...so what conclusions am I supposed to draw from that?"

To make it plain: Scientists are in no way opposed to investigating aliens (I don't know a single one who hasn't been into SciFi in some way or another) - but there is currently nothing there to investigate in a *scientific* manner.
Mimath224
1 / 5 (1) May 09, 2018
@antialias_physorg. Don't agree with you. I am intelligent enough to know scientist aren't magicians and that's a silly remark to make to one who spent his working life working with them and a regular to this and other science forums.
'To make it plain: Scientists are in no way opposed to investigating aliens...' What are you talking about? I never mentioned 'aliens'! You see, that's where the problem, you have turned everything I wrote to 'investigating aliens' which is an attempt to twist the conversation into a single, almost derogative, direction.
'Blob', again you attempt at the derogatory. If you don't want to discuss the phenomena seriously then say so and I will understand.
There are many incidents that have needed/do need a proper scientific investigation...but no, just like you, 'Oh it's about aliens' and they shy away. I, a layman in scientific terms, call it a phenomenon but it seems you insist on an 'alien' interpretation, which proves my point, doesn't it.
Eikka
not rated yet May 09, 2018

So what? How does that show getting something in orbit using beam power propulsion will always be impossible as you claimed?


Not always - it is theoretically possible - but not practically so for anything but small payloads.

In what way are the "power requirements are too enormous to handle"? Please don't make up crap.


The answer is staring at you in the face, but you refuse to see it: getting tens or hundreds of gigawatts of power and transmitting it (efficiently) to the target, converting it into propulsive power, is a gargantuan problem of engineering and logistics. You're talking a significant portion of the power output of an entire NATION to power a single launch.


Its volume is irrelevant. Its mass is what's relevant. Thus you make no sense.


You fail to understand the point: the power density goes up with launch mass because the target size doesn't scale up as fast as the target mass, so your materials can't keep up with the thermal load
Eikka
not rated yet May 09, 2018
It's going to be a pretty major advantage considering that's where the most fuel and most cost is.


The cost to launch is still going to be many many times too much.

Atmospheric density is going to be higher at the surface. That means beam propulsion is going to give a better thrust-to-weight ratio


Don't forget that denser air means more drag, and the rocket has to be built heavier to begin with to stand up against the higher gravity, mostly negating the advantage.

you can't see the math for this.


Let's talk math

https://en.wikipe...equation

The delta-V of the rocket is proportional to ln(m0/mf) where m0 is initial full mass with fuel, mf is mass without fuel. Let's assume exhaust velocity normalizes to 1.

Under earth's gravity, the fueled-to-empty ratio is 3:1. At the super-earth with 2.4 times the escape velocity, the ratio is 11:1. Note that the mass of the rocket structure is with the empty mass. (cont.)
antialias_physorg
2.3 / 5 (3) May 09, 2018
I never mentioned 'aliens'!

Then replace that with 'unexplained phenomena' (ghosts, religion, weird blobs on videos, eyewitness evidence, ... whatever).
The point remains: if you can't test it (because it's not reproducible) there's nothing a scientist can do more than a non-scientist.

I will discuss anything seriously when there is something serious to discuss - i.e. where there is substance that can be analyzed to the point where information can be gained. Without that we're just in wild speculation territory - and I find that of little value (Yes, I like to speculate about aliens, too, but mostly in the context of the novel I'm hoping to finish one day).

If you have a suggestion what to do about the evidence you think you have then do it. No one is stopping you. There is no 'scientist-license' you have to get to work as a scientist (or try to publish any findings for that matter). A PhD is not mandatory.
Eikka
not rated yet May 09, 2018
(cont.) With 10 units of fuel needed for 1 units of mass, even if you save 50% of the fuel by using the ambient air for the first stage, you're still going to be at 5:1 mass ratio, but, you also have to account for the fact that the rocket itself must be structurally heavier to account for the high gravity, so your payload fraction diminishes accordingly.

Let's say the payload on earth is optimistically half the empty rocket mass. Suppose then that the rocket on the super-earth needs to be three times heavier to stand - that diminishes the payload to 1/4 the rocket mass.

So, on earth you use 3 units of fuel to get 0.5 units to orbit. On the super-earth, you'd use 5 units of fuel to get 0.25 units to orbit.

6:1 versus 20:1

Atmospheric density is going to be higher at the surface. That means beam propulsion is going to give a better thrust-to-weight ratio


Actually, it doesn't mean that. The thrust is proportional to the energy delivered, not to atm density.
Eikka
not rated yet May 09, 2018
The atmospheric density is irrelevant, because the rocket can only gain velocity by the rate that you add energy to it, so your acceleration is limited by the amount of power you can beam up to it, whether you take in air for reaction mass, or carry it along in a tank.

Of course a lighter rocket is going to accelerate faster, but it would do so almost regardless of air density as long as sufficient reaction mass is available. At lower air densities, you'd simply use a bigger scoop to pull in the air.

Of course all these calculations are just rough back of the envelope math, and the reality is bleaker because things like masses of structures vs. their strength doesn't increase linearily - again because of the area vs. volume thing where the strength of a beam increases by its cross-section (r^2) while the mass increases with volume (r^3) so bigger beams aren't proportionally stronger. You get diminishing returns.
Eikka
not rated yet May 09, 2018
The point is, if you're a 1960's earth level of civilization just at the brink of space age, you don't have exotic means of propulsion like multi-gigawatt lasers at your disposal. You have chemical rockets, or at best nuclear rockets, and your launch fuel demands to orbit would be approximately 7-8 times greater than we had, or beyond. That's just my lowball estimate.

At your best effort and great cost, you might manage to launch a Sputnik, but that's assuming the planet can even sustain the level of technological civilization we have, instead of being an ecology full of inch-worms and elephant-like creatures that can't lift a stone without breaking a bone, or it's a flat ocean world.
Mimath224
1 / 5 (1) May 09, 2018
@antialias_physorg '...where there is substance that can be analyzed to the point where information can be gained...' Oh yes there have been & are many incidents where effects could be analysed but larger artifacts need expert handling to avoid contamination. But these incidents didn't/don't happen just a daytime. No, sometimes it means receiving a call at 1 a.m. and sacrificing one's 'comfort zone'. No good saying I'll come after breakfast because any effect may have gone and anything else worth testing has been confiscated by the authorities. The few scientist prepared to get their 'hands dirty' met with disapproval by other scientists and recruiting fellow scientist met with comments like Da Schneib's above 'So don't BS me about "flying saucers." (very scientific response I'm sure) and your interpretation 'investigating aliens'.
But I'm used to this attitude of misinterpretation and the use of expletives. Shame really, I thought previously that you two were objective but now...
antialias_physorg
1 / 5 (1) May 09, 2018
No good saying I'll come after breakfast because any effect may have gone and anything else worth testing has been confiscated by the authorities.

I think you have a very weird idea what a scientist is or what they can do. It's not like in the movies where a scientist goes to a place pulls out a tricorder and goes "Yep, analysis complete".

If you really have some stuff that requires serious analysis (let's say mass spectography or similar) then that can mean days in preparation.
And no...if these nebulous 'authorities' are so efficient that they can confiscate stuff between 1am and breakfast based on a call that wasn't targeted at them then I doubt a scientist could show up and do anything (much less hold these 'authorities' at bay with...erm...what exactly? A hearty: "Back off! I'm a scientist!" ?)
Da Schneib
1 / 5 (1) May 09, 2018
Under earth's gravity, the fueled-to-empty ratio is 3:1. At the super-earth with 2.4 times the escape velocity, the ratio is 11:1. Note that the mass of the rocket structure is with the empty mass. (cont.)

But you forgot to subtract from the structure for the unneeded first stage.

Figures don't lie, but liars figure. You're figuring again, @Eikka.
Mimath224
not rated yet May 09, 2018
@antialias_physorg
No good saying I'll come after breakfast because any effect may...

I think you have a very weird idea what a scientist... out a tricorder and goes "Yep, analysis complete".
If you really have some stuff that requires serious analysis (let's say mass spectography or similar) then that can mean days in preparation.
And no...if these nebulous 'authorities' are so efficient that they can confiscate...

Yes, fair enough, you have some valid points there but no I don't have a weird view of scientists, I worked with them all my working life and like any other community attitudes varied. But with the US world famous company we worked for DID want to know what you did in your spare time. It was all in the 'job description'. If there was a risk that you'd get injured (say in a martial art competition) this could affect your work and there was even less tolerance for the R&D scientist. They had to be 'company people'. (cont.)
Da Schneib
1 / 5 (1) May 09, 2018
In case anyone doubts me, here's the dope from Wikipedia in the very page @Eikka linked: https://en.wikipe...equation
The Tsiolkovsky rocket equation, or ideal rocket equation, describes the motion of vehicles that follow the basic principle of a rocket: a device that can apply acceleration to itself using thrust by expelling part of its mass...
Note that last part: part of its mass. If the rocket doesn't expel part of its mass, this equation doesn't apply. Noting that this is the first sentence in the definition on Wikipedia of this equation, @Eikka is either stupid or lying. Since @Eikka lies about any alternative energy or alternative propulsion, we can easily discern that @Eikka is lying again and knew perfectly well that its equation was not valid for beam propulsion using atmosphere as reaction mass.
Mimath224
not rated yet May 09, 2018
(cont.) The company didn't pay an excellent wage for nothing.
Don't misunderstand me, the company policy was (and still is) strict and there was no discrimination as to what one did in one's spare time.
While I couldn't 'recruit' any of them they helped me in other ways. The equipment they worked with was always maintained 'state of the art' as it were, and sometimes I could get permission to use it, such as nmr. I already worked chromatography equipment and well aware of having to calibrate first.
So I know of the scientist's predicament but from your previous comments I don't think you understand the predicaments a lay person out there in the real world. The big company executives think so far ahead they are way out in front. Unlike NSA or MI (whatever) they don't see the possible existence of aliens a threat what they see is a possible market slot. While I look at the night sky and wonder they see the Milky Way as a future vast expansion of their product.
Mimath224
not rated yet May 10, 2018
@Eikka I must admit that my astrodynamic books to not list the ideal rocket equation (at wiki). Instead they end with up a PDE for Impulse, thrust ratio and mass ratio. Any chance of you being more specific. Just asking.
Da Schneib
1 / 5 (2) May 10, 2018
Oh, and I almost forgot to mention: it also means @humy is right.
Merrit
5 / 5 (1) May 10, 2018
It is hard to say whether or not intelligent life would be even able to form on a super earth due to the much higher gravity strain. Life on earth evolved based on a different environment than a super earth. Certain adaptations would be more efficient in one versus the other. On a super earth any type of skeletal structure would need to be much stronger. But, this would likely make the material more dense as well. On earth something like this would be inefficient compared to our less dense bones
Merrit
not rated yet May 10, 2018
Maybe on a super earth walking is not efficient and life rolls around on the ground instead. So far we have only studied life on one planet. Until when/if we have studied life on lower and higher g planets, really kind of silly discussing what intelligent life could or couldn't do. Although, in the future we could possibly simulate it rather than actually trying to find life in the universe.
granville583762
5 / 5 (3) May 12, 2018
Escaping greater velocity than 25,000mph with no fuel

Taking sufficient fuel to reach orbital velocity to reach the planets, how do we in tend to propel are selves away from large planets we do not want to land on that have a greater escape velocity than 25,000mph!
jimsecor
not rated yet May 12, 2018
Of course, all of this is based on now technology and how things operate here on Earth and that the alien world's naatives are no more advanced than we are.
Mimath224
not rated yet May 12, 2018
@jimsecor
Of course, all of this is based on now technology and how things operate here on Earth and that the alien world's naatives are no more advanced than we are.

Also based, mainly, on life as we know it. Although perhaps physics dictate that life must evolve by a certain path but are we relying on this a little too much. The 'habitable zone' of exo-planets so far discovered is really about being habitable for life similar to our own. I often wonder if life might evolve differently on exo-planets say, close to but not in a habitable zone. That is, by taking example of microorganisms on Earth in extreme conditions, on exo-planets just outside the habitable zone might have such organisms in abundance. Would these organism then evolve? Just wondering, that's all.

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