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Inhabitable planets at doable distances ever or somewhere?

by Gerinski
Tags: distances, doable, inhabitable, planets
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Gerinski
#1
Aug31-14, 06:29 AM
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In our time epoch and location in space, it seems that even if we received signals of some extraterrestial civilization, or detect some extrasolar inhabitable planet, unless we would achieve some huge breakthroughs it would be impossible to ever visit each other.

But can we conceive of other places where star density is much higher than in our vicinity, or perhaps much earlier epochs when the universe was much smaller so all stars were much closer to each other, where several inhabitable planets may have been close enough to each other so as to make space travel between them for any eventual advanced civilizations developing in them feasible?

A related question, would life have been possible at those much earlier epochs when star systems were much more densely packed? As from which age of the universe would heavy elements be present in enough quantity so as to permit life to emerge in suitable planets? Or were cosmic cataclysms too frequent for any emerging life to survive for long enough?
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mathman
#2
Aug31-14, 03:46 PM
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Problems:
(1) Early universe had no elements other than H, He, and a little Li. Other elements are created in stars.
(2) Intelligent life seems to require a long time to evolve. Our planet is ~ 4.5 billion years old. Space travel is ~ 50 years.
mfb
#3
Aug31-14, 04:56 PM
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A higher density of stars is problematic for the stability of planetary orbits.
An easy way to get civilizations to be able to visit each other are systems with more than one inhabitated planet / moon. If Mars would have life similar to Earth, I'm sure we would have been there already.

As from which age of the universe would heavy elements be present in enough quantity so as to permit life to emerge in suitable planets?
With just one known sample of life, this is hard to answer.

Gerinski
#4
Aug31-14, 05:33 PM
P: 132
Inhabitable planets at doable distances ever or somewhere?

Thanks, but, are not in the current epoch (I mean somewhere else, perhaps very far away but at the same epoch from the BB as we are, so there has been time enough for enough heavy elements to form and for intelligent life to develop) where stars are much closer to each other? Surely closer to the galactic centers star systems are more densely packed, right? Sitting in one of those planets one would see a relatively bright sky even in the 'night' due to the many stars at close distance, and suns with inhabitable planets might not be too far away?
Ophiolite
#5
Aug31-14, 06:56 PM
P: 288
I would not automatically rule out the possibility of inter-stellar travel for humans. I agree it would require breakthroughs, but even setting aside traveling at a significant percentage of c, in order to benefit from time dilation, there are at least three possibilities:
1. Generation ships.
2. Hibernation.
3. Frozen embryos and educator robots.

You have also ignored the possibility that if there are other intelligent species, they may have much longer life spans, in which case a travel time of a century or two may not be a concern.
enorbet
#6
Aug31-14, 07:10 PM
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I'm afraid "too far" is relative to travel speed. People traveling just to Europa or Titan is a very long way away. Presently it takes roughly 3-5 years to traverse the distance (roughly 4 AU) to Europa at currently practical speeds. It would take roughly 20-35 years to get to Pluto at an average of 40 AU. You might reach the Oort Cloud at a little more than 5,000 AU if you could live to be 400 years old, and we are still not even to close to the nearest star. The Oort Cloud is unimaginably big, stretching from roughly 5,000 AU away to a whopping 100,000 AU.

Voyager 1 didn't have to accelerate people and supplies to keep them alive for almost 40 years, so coming in at well under 1 ton, it was practical to achieve speeds useful in the so-called slingshot gravity assist boost. It has attained the incredible speed of 17 km/s, roughly 38,000 mph. Getting human occupied craft to such speeds is a problem for which we have no practical solutions yet. Even at that incredible and presently impractical speed Voyager 1 has traveled for almost 37 years, it has traversed only 128 AU. This is not meant to demean it's amazing achievement, but only to put into perspective how far we are from anything remotely resembling Interstellar travel.

In another thread there is a link to a wonderful but very humbling graphic representation of how far our earliest radio waves have reached within our galaxy at essentially lightspeed for roughly 100 years. It's BIG out there and we have barely begun.
mfb
#7
Aug31-14, 07:29 PM
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Gravitational slingshots work the same way for every spacecraft mass (as long as it is tiny compared to the planet masses...), but the resulting speed is limited to the order of 10km/s (30 000 years per light year).
Faster spacecrafts could still use this, but it would just be a tiny contribution to the total velocity.

If reaching a star is our goal, it is pointless to send something now - it would be surpassed by faster spacecrafts long before it even comes close.

Quote Quote by Gerinski
Thanks, but, are not in the current epoch (I mean somewhere else, perhaps very far away but at the same epoch from the BB as we are, so there has been time enough for enough heavy elements to form and for intelligent life to develop) where stars are much closer to each other? Surely closer to the galactic centers star systems are more densely packed, right? Sitting in one of those planets one would see a relatively bright sky even in the 'night' due to the many stars at close distance, and suns with inhabitable planets might not be too far away?
If you have planets in stable orbits there (and without constant bombardement by asteroids) - that is a big "if".
Chronos
#8
Sep1-14, 01:28 AM
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Lacking some rather stunning technological advances, the prospects of human travel beyond our solar system are slim. The energy requirements, as well as economics involved, are impractical.
mfb
#9
Sep1-14, 03:19 AM
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Quote Quote by Chronos View Post
Lacking some rather stunning technological advances, the prospects of human travel beyond our solar system are slim. The energy requirements, as well as economics involved, are impractical.
We had many stunning technological advances in the past. I would be surprised if we didn't have some in the future.
enorbet
#10
Sep1-14, 06:31 AM
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Quote Quote by mfb View Post
Gravitational slingshots work the same way for every spacecraft mass (as long as it is tiny compared to the planet masses...), but the resulting speed is limited to the order of 10km/s (30 000 years per light year).
Faster spacecrafts could still use this, but it would just be a tiny contribution to the total velocity.

If reaching a star is our goal, it is pointless to send something now - it would be surpassed by faster spacecrafts long before it even comes close.

If you have planets in stable orbits there (and without constant bombardement by asteroids) - that is a big "if".
I'm aware that gravity slingshots are also practical for manned craft but that doesn't change the entry speeds required to reach the velocity of Voyager (let alone higher ones) and vastly more mass requires vastly more energy which translates into longer burns which equals heavier fuel requirements.

My main point is that given these vast distances chemical rockets will not suffice.
mal4mac
#11
Sep1-14, 07:09 AM
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Quote Quote by mfb View Post
A higher density of stars is problematic for the stability of planetary orbits.
Interesting! Anyone worked out what percentage of stars might be relegated from having a "second earth" through being in an over-dense region? We are on the outer edge of our galaxy, which is a fairly loose spiral. Maybe only stars in such a position can have an earth?

This might have repercussions on the Fermi question: "Where are they?"
mfb
#12
Sep1-14, 02:31 PM
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This is related to the topic of the galactic habitable zone. Reference 16 there deals with gravitational perturbations.

There are billions of stars with an environment similar to our sun, so this does not answer the Fermi paradox.
Chronos
#13
Sep1-14, 05:49 PM
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The pessimistic, yet, possible answer to the Fermi question is interstellar space travel is a technological challenge that has not been solved.


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