Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

nasa.gov

Post reply on HN
Print view View original

81–90 of 142 posts

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

#81

Post by NoMoreNicksLeft »

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.

It's quite simple really. All we need is fast-as-light technology.

If you get in a ship and travel to Alpha Centauri at the speed of light, the travel seems instantaneous to you. But the people you leave behind think you've been gone 8 years when you return.

So instead, I propose that when the ship launches, we also propel the rest of the universe in the opposite direction also at the speed of light. Then, when the astronaut is scheduled to return, we propel the entire universe at the speed of light back to its original location.

All of reality undergoes time dilation. And the trip is basically instantaneous for all involved†.

† Note: This form of FTL is mildly costly in regards to energy expenditure.

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

#82

Post by perihelions »

What an unintuitive and sketchy-looking Bayesian model. They only have 11 chemicals in the database they're matching that messy IR spectrum against: 6 reasonable ones, and 5 bullshit ones that are only there because theory papers suggested that they'd be biomarkers of alien life. And, fit to just those 11 chemicals, the best-fit includes one of the bullshit ones (dimethyl sulfide, (CH₃)₂S).

https://stsci-opo.org/STScI-01HA2G716KS9YGAGVY1WBVFJ8Y.pdf

Is this approach, like, sane? I'm not a Bayesian statistics expert.

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

#83

Post by ericbarrett »

fmobus wrote: post #47
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…

I think 8g would be pretty hard to escape from, at least with chemical rockets.

Earth's surface gravity is really on the edge of what's feasible for chemical rockets; IIRC the limit is around 1.4g. Though as other commenters have mentioned, it's possible to have a much more massive planet that's also got a larger radius and thus has comparable surface gravity.

Some fun trivia—the planet Kerbin from Kerbal Space Program is the opposite case. It has a radius of 600km, versus Earth's 6378km, but is exactly 1 Earth g on the surface. This implies it's over 10x as dense.

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

#84

Post by everyone »

jdblair wrote: post #50
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 classic sci-fi "Mission of Gravity" explores what life would be like on a rapidly rotating planet where one experiences 3g at the equator and 700g at the poles. https://en.wikipedia.org/wiki/Mission_of_Gravity

Thanks for that! I need a new novel to read, just downloaded it!

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

#85

Post by littlestymaar »

behnamoh wrote: post #24
v8xi wrote: post #14

In Nick Lane's Oxygen: The Molecule that Made the World, he talks about the importance of both methane and carbon dioxide and how they exist at the extremes of a complex metabolic oxidation-reduction cycle. Methane stores a lot of chemical energy in its C-H bonds which can be burned directly, or metabolized through repeat oxidation events to ultimately form CO2, which plants utilize with the help of the sun to form m…

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…

In addition to what others have said about the fact this planet doesn't have 8g at its surface, at 8g you could still have many lifeforms that exists on earth, but only the small ones. Gravity grows roughly as the cube of your size (because your volume does), but bones resistance only get n² (because it's the surface that counts), so the bone resistance / weight ratio is inversely proportional to your size.

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

#86

Post by gus_massa »

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…

Can I help the GP?

In the paper they analyze 3 models, "no offset", "offset" and "offsetx2". It's strange that they get better fit for CO2 and CH3 en the "offsetx2" model, but in that model the DMS disappears. So there it at least one model.

Also, they analyze common molecules like CO2, CH4, H2O, NH3 and biologically interesting molecules like CH3-S-CH3 (DMS), HCN, CH3-Cl. From the discussion in the paper it looks like the CH3- part is important, so I'd like to see a brute force search with everything that is in https://en.wikipedia.org/wiki/Atmosphere_of_Titan and has a methyl group, like CH3-CCH, CH3-CN. My Chemistry and Astronomy is no so good, so I'd like to add CH3-OH, CH3-NH2, CH3-SH, CH3-CHO and a few more from https://en.wikipedia.org/wiki/List_of_interstellar_and_circu... I removed the ones that are big or has too many oxygen (like CH3-COOH).

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

#87

Post by adolph »

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.

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...

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

#88

Post by gus_massa »

divbzero wrote: post #79

> "Our ultimate goal is the identification of life on a habitable exoplanet, which would transform our understanding of our place in the universe," concluded Madhusudhan. What sort of observation or measurement would allow us to identify life on an exoplanet?

A lot of O2. As far as we know, the only source of a lot of O2 in the atmosphere are photosynthetic bacteria-like. So it will be a clear sign of life.

There are some more subtle cases, like the one discussed in this paper.

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

#89

Post by jandrese »

holoduke wrote: post #74
jandrese wrote: post #52

Earlier quoted context omitted.

Even worse if we are still limited by Newtonian dynamics it will take thousands of years for a probe to reach there. The rocket equation is a harsh mistress. In practical terms we will never visit that world without completely upending physics as we know it.

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 your rocket to accelerate you don't get to go anywhere outside of our solar system.

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

#90

Post by pdonis »

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...

> That is if density remains constant.

No, the calculation I made did not assume constant density. I just used the direct Newtonian formula for surface gravity and plugged in the known mass and radius of the planet. (You could also use that known mass and radius to calculate the average density. But you don't need to do that to calculate the surface gravity.)

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

But we know it isn't. We know the planet's radius is 2.6 times the Earth's radius. That's stated in the article.

Post reply on HN