5 ms·

36% larger radius than Earth means ~2.5x more volume. If it has a similar density to Earth 2.5g would probably stretch the definition of habitable for humans. T

36% larger radius than Earth means ~2.5x more volume. If it has a similar density to Earth 2.5g would probably stretch the definition of habitable for humans. This doesn't rule out habitation by other life, of course. Cool that we're finding interesting planets though! An actually human-habitable planet would, I think, have a significant cultural impact here on Earth.

ShredKazoo 4y ago
2.5g means you weigh 2.5 times as much. So if you're 150lbs on Earth that means you'd weigh 375lbs on this new planet. Weighing 375lbs is certainly inconvenient, but it's not like habitation at 375lbs is impossible, especially if you have a scooter. I wonder what happens if a human child grows up in a 2.5g environment. I imagine they grow up to be short, stocky, and extremely muscular. Adaptation probably plays a big role here. If you give a 150lb person a suit that weighs 225 lbs and tell them to wear it all the time, they probably give up after a few days. But if you tell a 150lb person to eat more until they're 375lbs, their body has time to adapt. Since the new planet is 100 light years away, even at the speed of light we're talking about a 100-year journey minimum. Maybe the generation ship used to make the journey could use artificial gravity to smoothly transition from 1g to 2.5g over the course of 100 years. Loading the ship with people who are stocky & muscular is another option. I don't think living in enhanced gravity needs to be terrible. Astronauts have to exercise more in order to maintain fitness in low-gravity environments. It appears to follow that if you're living in an enhanced-gravity environment, you can get away with exercising a lot less and still maintain fitness :-)
spaceman_2020 4y ago
What evolutionary changes would human beings need to adapt to 2.5g?
- gizajob 4y ago
  Thicker legs
- otikik 4y ago
  It might be more feasible to remove a big chunk of matter from the planet in question
- avereveard 4y ago
  Id's say a stronger circulatory sistem. Muscles and bone density will need to increase, but we do that as part of adaptation, evolution will favor the trait long term but regular use will already compensate in part or totally the need. Possibly ankles and knees will need to get stronger as well
- callamdelaney 4y ago
  We would only be adapting to 1.36g according to mamikonyana - this sounds more plausible. Because gravity is a function of size, mass and density. Not only mass.
a3w 4y ago
same density, higher size does not mean 2.5 g. Only some of that mass is below you. Some is to the front, right, back, left, where vectors in sum are zero.
- throwawaymaths 4y ago
  This is incorrect, the decrease comes from being at a higher altitude from the center of the planet, see gauss' law for gravity. If you kept the altitude the same the force would be exactly proportional as expected.
- anonymous_sorry 4y ago
  Also, all the "extra" mass is further away from you, and gravitation is proprtional to distance cubed. Interesting. Apparently surface gravity is proportional to mass/radius^2 [0] Assuming constant density as per the grandparent, the mass increases with the cube of the radius. Which simplifies to surface gravity being proportional to the radius of the planet. [0] https://en.m.wikipedia.org/wiki/Surface_gravity https://en.m.wikipedia.org/wiki/Surface_gravity
mamikonyana 4y ago
It actually gets you 1.36g, given the same density (your assumption) and using the fact that you are further away from the center of mass you get g ~ density x radius [0] [0] https://en.wikipedia.org/wiki/Gravity_of_Earth#Depth https://en.wikipedia.org/wiki/Gravity_of_Earth#Depth
chasil 4y ago
More importantly, this sounds like planets tidally locked around a red dwarf. Red dwarfs are known for flares that would destroy the atmosphere of any nearby planet. "Although this planet orbits very close to its star, at a distance about 10 times shorter than that of Mercury around our Sun, the amount of stellar irradiation it receives is still low... the star LP 890-9 is about 6.5 times smaller than the Sun and has a surface temperature half that of our star."
- ncmncm 4y ago
  In any case all its water would be locked up in ice on the night side.
  - callamdelaney 4y ago
    If only we could invent a method to turn ice into water..
    - ncmncm 4y ago
      Needs heat. But that is all found thousands of km away.
      - dylan604 4y ago
        Just use mirrors strategically placed so that light can bounce around the horizon so solar can be used to melt the ice. Or orbit a giant mirror beaming that heat source down. The fact that you think thousands of km away is a hard limit just means you're not fully caffinated just yet.
        ncmncm 4y ago
        If you are in orbit, why land on it at all? Surely there are construction materials and ice only light-minutes away and not so deep down a gravity well. God knows there is nothing else down there of any interest.
shireboy 4y ago
Assuming organisms adapted to live there, it would be harder for them to reach escape velocity to leave their planet. Is there a cut-off where known physics says it’s impractical to leave a planet? Ie the most powerful practical fuel wouldn’t be enough for any mass to reach escape velocity?
- jmillikin 4y ago
  https://space.stackexchange.com/questions/14383/how-much-bigger-could-earth-be-before-rockets-wouldnt-work/17576#17576 https://space.stackexchange.com/questions/14383/how-much-big... There's a table in that link of how much reaction mass is needed to reach orbit. At 1.5g it requires about 500% as much rocket as Earth. At 2.5g the number is ... much larger.
est31 4y ago
> 36% larger radius than Earth means ~2.5x more volume. If it has a similar density to Earth 2.5g would probably stretch the definition of habitable for humans. Volume scales cubically, yes. And therefore, also does the gravitational pull by the object at the same distance to the center. But due to the larger radius, you are also further away. Gravity respects the inverse square law. This means that the surface gravity of an object that maintains the same density increases linearly with the object's size. In other words, you would have 1.36g on the planet's surface, not 2.5g. But that's assuming same density. Even within our own solar system this is not true: Mars's surface gravity is 0.38 of earth's gravity but 0.53 of earth's radius. The gravity is lower than it would be if Mars had the same density as earth.

ShredKazoo 4y ago

2.5g means you weigh 2.5 times as much. So if you're 150lbs on Earth that means you'd weigh 375lbs on this new planet. Weighing 375lbs is certainly inconvenient, but it's not like habitation at 375lbs is impossible, especially if you have a scooter. I wonder what happens if a human child grows up in a 2.5g environment. I imagine they grow up to be short, stocky, and extremely muscular. Adaptation probably plays a big role here. If you give a 150lb person a suit that weighs 225 lbs and tell them to wear it all the time, they probably give up after a few days. But if you tell a 150lb person to eat more until they're 375lbs, their body has time to adapt. Since the new planet is 100 light years away, even at the speed of light we're talking about a 100-year journey minimum. Maybe the generation ship used to make the journey could use artificial gravity to smoothly transition from 1g to 2.5g over the course of 100 years. Loading the ship with people who are stocky & muscular is another option. I don't think living in enhanced gravity needs to be terrible. Astronauts have to exercise more in order to maintain fitness in low-gravity environments. It appears to follow that if you're living in an enhanced-gravity environment, you can get away with exercising a lot less and still maintain fitness :-)

spaceman_2020 4y ago

What evolutionary changes would human beings need to adapt to 2.5g?

gizajob 4y ago
Thicker legs
otikik 4y ago
It might be more feasible to remove a big chunk of matter from the planet in question
avereveard 4y ago
Id's say a stronger circulatory sistem. Muscles and bone density will need to increase, but we do that as part of adaptation, evolution will favor the trait long term but regular use will already compensate in part or totally the need. Possibly ankles and knees will need to get stronger as well
callamdelaney 4y ago
We would only be adapting to 1.36g according to mamikonyana - this sounds more plausible. Because gravity is a function of size, mass and density. Not only mass.

a3w 4y ago

same density, higher size does not mean 2.5 g. Only some of that mass is below you. Some is to the front, right, back, left, where vectors in sum are zero.

throwawaymaths 4y ago
This is incorrect, the decrease comes from being at a higher altitude from the center of the planet, see gauss' law for gravity. If you kept the altitude the same the force would be exactly proportional as expected.
anonymous_sorry 4y ago
Also, all the "extra" mass is further away from you, and gravitation is proprtional to distance cubed. Interesting. Apparently surface gravity is proportional to mass/radius^2 [0] Assuming constant density as per the grandparent, the mass increases with the cube of the radius. Which simplifies to surface gravity being proportional to the radius of the planet. [0] https://en.m.wikipedia.org/wiki/Surface_gravity https://en.m.wikipedia.org/wiki/Surface_gravity

mamikonyana 4y ago

It actually gets you 1.36g, given the same density (your assumption) and using the fact that you are further away from the center of mass you get g ~ density x radius [0] [0] https://en.wikipedia.org/wiki/Gravity_of_Earth#Depth https://en.wikipedia.org/wiki/Gravity_of_Earth#Depth

chasil 4y ago

More importantly, this sounds like planets tidally locked around a red dwarf. Red dwarfs are known for flares that would destroy the atmosphere of any nearby planet. "Although this planet orbits very close to its star, at a distance about 10 times shorter than that of Mercury around our Sun, the amount of stellar irradiation it receives is still low... the star LP 890-9 is about 6.5 times smaller than the Sun and has a surface temperature half that of our star."

ncmncm 4y ago
In any case all its water would be locked up in ice on the night side.
- callamdelaney 4y ago
  If only we could invent a method to turn ice into water..
  - ncmncm 4y ago
    Needs heat. But that is all found thousands of km away.
    - dylan604 4y ago
      Just use mirrors strategically placed so that light can bounce around the horizon so solar can be used to melt the ice. Or orbit a giant mirror beaming that heat source down. The fact that you think thousands of km away is a hard limit just means you're not fully caffinated just yet.
      - ncmncm 4y ago
        If you are in orbit, why land on it at all? Surely there are construction materials and ice only light-minutes away and not so deep down a gravity well. God knows there is nothing else down there of any interest.

shireboy 4y ago

Assuming organisms adapted to live there, it would be harder for them to reach escape velocity to leave their planet. Is there a cut-off where known physics says it’s impractical to leave a planet? Ie the most powerful practical fuel wouldn’t be enough for any mass to reach escape velocity?

jmillikin 4y ago
https://space.stackexchange.com/questions/14383/how-much-bigger-could-earth-be-before-rockets-wouldnt-work/17576#17576 https://space.stackexchange.com/questions/14383/how-much-big... There's a table in that link of how much reaction mass is needed to reach orbit. At 1.5g it requires about 500% as much rocket as Earth. At 2.5g the number is ... much larger.

est31 4y ago

> 36% larger radius than Earth means ~2.5x more volume. If it has a similar density to Earth 2.5g would probably stretch the definition of habitable for humans. Volume scales cubically, yes. And therefore, also does the gravitational pull by the object at the same distance to the center. But due to the larger radius, you are also further away. Gravity respects the inverse square law. This means that the surface gravity of an object that maintains the same density increases linearly with the object's size. In other words, you would have 1.36g on the planet's surface, not 2.5g. But that's assuming same density. Even within our own solar system this is not true: Mars's surface gravity is 0.38 of earth's gravity but 0.53 of earth's radius. The gravity is lower than it would be if Mars had the same density as earth.