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Webb Discovers Methane, Carbon Dioxide in Atmosphere of K2-18B

nasa.gov

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Re: Webb Discovers Methane, Carbon Dioxide in Atmosphere of K2-18B

#101

Post by dylan604 »

adriand wrote: post #98
dylan604 wrote: post #27

Earlier quoted context omitted.

The gravity question is one I've pondered myself as a thought exercise. There's been discussions on how far up a plant can draw water as the defining limit to how tall a tree could grow. Some discussions as well on how tall an animal could grow based on how high blood could be pumped up. Which is a direction different from the structural support and sizes that I find interesting.

I can imagine an intelligent species on a high-G planet scratching their “heads” and wondering, as they surveil Earth, how anything could possibly survive on such a low-G planet.

like humans trying to determine how to survive on moon bases or Martian colonies?

Re: Webb Discovers Methane, Carbon Dioxide in Atmosphere of K2-18B

#102

Post by OkayPhysicist »

wheels wrote: post #48
behnamoh wrote: post #24

Earlier quoted context omitted.

I wonder what life looks like on a planet which is over 8 times more massive than the Earth. Do animals have spines at all on a planet with almost 8g gravity? Does life even get to evolve into complex systems like animals under this much gravity? How about plants? Do they grow up or spread out instead? If one day we get a visitor from this planet, they'll jump on our planet the same way human astronauts jumped on the…

Gravity is only about 1.25 g, according to Wikipedia. Density matters. The earth and Saturn have about the same surface gravity.

Comparing rocky planets, density doesn't really matter at all. The range of possible densities for rocky planets is tightly constrained. What matters is the fact that surface gravity scales sub-linearly with regards to a planets mass.

  M = 4/3*pi*r^3*d
  r = (4/3*pi*d/M)^(-1/3)
  a = GM/r^2
  a = GM(4/3*pi*d/M)^(2/3)
  a = G(4/3*pi*d)^(2/3) * M^(1/3)

Re: Webb Discovers Methane, Carbon Dioxide in Atmosphere of K2-18B

#103

Post by mr_toad »

adolph wrote: post #87
pdonis wrote: post #53

Earlier quoted context omitted.

The planet's surface gravity is not 8 g. Surface gravity goes like mass over radius squared, and the planet's radius is 2.6 times Earth's, so the surface gravity will be 8 / (2.6)^2, or only about 1.2 times that of Earth.

That is if density remains constant. If the planet were 8x mass but with same radius, gravity would be 8 g, or 8 × 9.795 m/s^s. Earth mass: 5.97×10^24 kg, 6378.137 km yields 9.795 m/s^2 8x mass: (8×5.97)×10^24 kg, 6378.137 km yields 78.36 m/s^2 All calculations: https://www.wolframalpha.com/input?i=surface+gravity+calcula...

> If the planet were 8x mass but with same radius

That’s not possible for normal stable matter. The Earth’s density is about 5g per cubic centimetre. Iron is 7.8g per cubic centimetre. Osmium is the densest stable element at 22.6g per cubic centimetre.

Re: Webb Discovers Methane, Carbon Dioxide in Atmosphere of K2-18B

#104

Post by shepardrtc »

no_wizard wrote: post #60
lofaszvanitt wrote: post #30

120 light years away. Time to get the ufo tech out already.

is Faster Than Light travel even possible? I'm asking in a serious way. I have always read that its impossible, at least within our current knowledge. the only semi-plausible theory I've ever heard is that Blackholes might one day yield some way of traveling quickly across the universe but nobody has shown anything substantiated around that or anything else.

You can't go FTL through spacetime. But some math shows that it might be possible to warp spacetime around you and propel you to somewhere faster than it would take light going through spacetime.

Re: Webb Discovers Methane, Carbon Dioxide in Atmosphere of K2-18B

#105

Post by saltcured »

treyd wrote: post #57
julienchastang wrote: post #13

Earlier quoted context omitted.

From a single pixel of light! Indeed mind blowing.

That's somewhat misleading though. It's not really a pixel in that there's much more information available than, basically, 3 integers between 0 and 255. There's 4 instruments on the telescope that collect 4 different chunks of IR spectra, and there's very precise and granular intensity values for light received around any given wavelength. Much more detail than a "pixel" has in the typical sense we use them. It's no…

It's a crude analogy, but I like to tell people that a spectroscope is more like a highly directional microphone to listen to molecules than it is like any normal camera...

Re: Webb Discovers Methane, Carbon Dioxide in Atmosphere of K2-18B

#106

Post by mr_toad »

jandrese wrote: post #89
holoduke wrote: post #74

Earlier quoted context omitted.

We just need a 1g rocket. Will take only a few days to get there. Life on earth will be 1000 years ahead once we are back though.

The problem is when you work out the math on rocket that can sustain 1G for multiple days with any Earthly isp you realize the math just doesn't work. Even if you go nuts and plug in a number like 1 million seconds (our best chemical rockets are more like 450 seconds) for the isp it is still nowhere close to feasible using only the mass of our solar system. As long as you are stuck flinging mass out of the back of yo…

A beamed core proton-antiproton rocket could produce millions of ISP and allow accelerations of up to 0.7C, using relativistic mesons as the reaction mass. It is entirely theoretical though.

https://ntrs.nasa.gov/api/citations/20200001904/downloads/20...

Re: Webb Discovers Methane, Carbon Dioxide in Atmosphere of K2-18B

#107

Post by blackoil »

coldpie wrote: post #76
no_wizard wrote: post #60

Earlier quoted context omitted.

is Faster Than Light travel even possible? I'm asking in a serious way. I have always read that its impossible, at least within our current knowledge. the only semi-plausible theory I've ever heard is that Blackholes might one day yield some way of traveling quickly across the universe but nobody has shown anything substantiated around that or anything else.

FTL travel being impossible is basically the one thing where I completely irrationally reject the science :) It's just too depressing for me to accept. There's gotta be a loophole. There's just gotta be...

It's super easy, barely an inconvenience. Bend space time to create a wormhole.

Re: Webb Discovers Methane, Carbon Dioxide in Atmosphere of K2-18B

#108

Post by kemmishtree »

joshlemer wrote: post #45
behnamoh wrote: post #24

Earlier quoted context omitted.

I wonder what life looks like on a planet which is over 8 times more massive than the Earth. Do animals have spines at all on a planet with almost 8g gravity? Does life even get to evolve into complex systems like animals under this much gravity? How about plants? Do they grow up or spread out instead? If one day we get a visitor from this planet, they'll jump on our planet the same way human astronauts jumped on the…

It would be really cool to run an experiment like this. Have some population of rats living in a large enclosure that is held in a large centrifuge for decades and see how they evolve.

Just put e. coli in an ultracentrifuge and do a few hundred generations of serial passaging and see what evolves, for starters. You could do this pretty cheaply without waiting decades or killing mammals. Apparently e. coli can proliferate happily at almost half a million g... https://phys.org/news/2011-04-bacteria-extreme-gravity.html#....

Re: Webb Discovers Methane, Carbon Dioxide in Atmosphere of K2-18B

#109

Post by nextaccountic »

bigbillheck wrote: post #73
nofitty376 wrote: post #54

That spectrum is so noisy. How can they infer the blue fit from the (noisy) white points? The data look almost consistent with flat (no detection). And even if there is a detection, it looks like many other models could potentially fit the data...

> How can they infer the blue fit from the (noisy) white points? By having a detailed model, and modern probabilistic techniques: The planet’s terminator is modelled as a plane-parallel atmosphere in hydrostatic equilibrium, with uniform chemical composition. The chemical abundances and pressure-temperature (P-T) profile are free parameters in the model. The retrieval framework follows a free chemistry approach, wher…

what means planet's terminator?

Re: Webb Discovers Methane, Carbon Dioxide in Atmosphere of K2-18B

#110

Post by thot_experiment »

pdonis wrote: post #53
behnamoh wrote: post #24

Earlier quoted context omitted.

I wonder what life looks like on a planet which is over 8 times more massive than the Earth. Do animals have spines at all on a planet with almost 8g gravity? Does life even get to evolve into complex systems like animals under this much gravity? How about plants? Do they grow up or spread out instead? If one day we get a visitor from this planet, they'll jump on our planet the same way human astronauts jumped on the…

The planet's surface gravity is not 8 g. Surface gravity goes like mass over radius squared, and the planet's radius is 2.6 times Earth's, so the surface gravity will be 8 / (2.6)^2, or only about 1.2 times that of Earth.

Juuuuusssttt barely below the limit to be able to launch chemical rockets into space (IIRC it's ~1.3g)
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