If one day we get a visitor from this planet, they'll jump on our planet the same way human astronauts jumped on the Moon.
For example, the Earth is 10 times more massive than Mars, but only has 2.6 times surface g.
Higher gravity means this upper limit will be smaller. All sorts of similar scaling things will change optimum points for structural and energy reasons.
Higher gravity certainly means higher pressure gradient, more pressure per vertical meter of ocean. And high pressure affects protein structure.
It's life, but not as we know it.
Assuming life develops in an ocean, like we did, organisms in water are essentially weightless, regardless of the g force.
https://stsci-opo.org/STScI-01HA2G716KS9YGAGVY1WBVFJ8Y.pdf
Is this approach, like, sane? I'm not a Bayesian statistics expert.
[0] https://global.oup.com/academic/product/planetary-systems-a-...
I wonder how old this world is, and how stable its enviroment is/has been. Complex animal life took 3.5 bn years to emerge on Earth, of course that's a meaningless data point by itself but intuitively for this place to have an ecosystem or complex life it needs to be old.
Still, even without this what a wonderful and weird environment.
That being said, there was an experiment (https://www.pnas.org/doi/full/10.1073/pnas.1115323109) which was able to select single cellular organisms to "become multicellular" in a rapid amount of time (<50 generations? been a while since I read it). Which says to me that, theoretically, the process is not hard, it just requires trillions of attemps to evoke something that works.
How certain are we it took that long (the first time)?
I'm not so sure about that. I mean, at the moment both are impossible, but it's much easier to imagine traveling 4ly than 124ly. 4ly can be reached in a single lifetime if you accelerate a shop to .9c, which is technically possible. 124ly is going to be a multigenerational undertaking no matter what. The 248y communication lag is also a much bigger obstacle than an 8y lag.
I think once you can travel 124ly, you can travel 1000+ ly. You need to be completely self-sufficient and you're going to lose contact with home anyway. If you send a robot, you're not going to hear from that robot again in centuries, if ever.
We all sit around knowing to listen to the skies sometime in October of 2185 to hear if the rover found life within the first month of its landing.
If we ever send a team to live there, we'd hear broadcasts of their lives from 125 years prior. A real portal in time - so cool.
Had not heard of dimethyl sulfide before. That's a good keyword to know.
An amazingly long time ago.
It's not a lot of information, not nearly enough to identify surface features on an exoplanet, but it's very useful data if you're trying to identify likely chemical composition of bodies or how hot clouds of gas are.
Given a sufficient quantity of reactants/reagents, could DMS be produced via a natural process, or is this a sufficiently unfavorable reaction that it's unlikely?
2 CH3OH + H2S → (CH3)2S + 2 H2O
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.
K2-18b (name of the exo-planet) orbiting star K2-18 was discovered in 2015 but the water was not detected until 2019.
Very unpleasant planet.
What sort of observation or measurement would allow us to identify life on an exoplanet?
There are some more subtle cases, like the one discussed in this paper.
https://arxiv.org/abs/1802.08421
...and an excellent video on the topic:
> DMS is generated by the degradation of dimethylsulfoniopropionate, which is present in many species of marine algae and plants, including dinoflagellates and coccolithophores
Preprint: https://arxiv.org/abs/1909.05218
Figure 2 pp. 14 of the preprint shows much more plausible error bounds on the curve fit. That press release "best fit" curve is merely an artist's conception.
The preprint of the Webb based paper is here [0] from here [1].
[0]: https://stsci-opo.org/STScI-01HA2G716KS9YGAGVY1WBVFJ8Y.pdf
[1]: https://webbtelescope.org/contents/news-releases/2023/news-2...
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, whereby the individual mixing ratio of each chemical species is a free parameter.... Our canonical model comprises of 22 free parameters overall: 11 corresponding to the individual mixing ra- tios of the above chemical species, 6 for the P-T profile, 4 for the clouds/hazes and 1 for the reference pressure Pref , defined as the pressure at a fixed planetary radius of 2.61 R⊕. The Bayesian inference and parameter estimation is conducted using the MultiNest nested sam- pling algorithm (Feroz et al. 2009) implemented through PyMultiNest.
(Sections 2.4 and 3.1 from https://stsci-opo.org/STScI-01HA2G716KS9YGAGVY1WBVFJ8Y.pdf)
> And even if there is a detection, it looks like many other models could potentially fit the data...
Name three.
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).
The bump at 4.3um looks real, and it seams to be an standard absorción of CO2. https://www.quora.com/Does-CO2-absorb-all-infrared-frequenci...
The bump at 1.2, 1.4 and 2.4um looks real. I found this showing a peak for CH4 at 2.325um. http://www.astrochem.org/data/CH4H2O.php
[Sorry for the sources, but I'm not an expert is spectroscopy.]
My guess is that they assumed something like
a% * CH4 + b% * CO2 + c% * H2O + others
and get the best fit for a%, b%, c%, ... using the white points. Later, using these numbers they draw the blue line.
The peak for DMS is not clear for my untrained eye, so I can't guess what they did there. (Perhaps it's just the best fit.) It would be nice to see the a graph of the blue line they guessed with DMS and a superimposed red line with and atmosphere with an alternative atmosphere where the DMS is replaced with something uninteresting (N2? H2O? More CH4? I have no idea what is uninteresting here.)
[0]: https://stsci-opo.org/STScI-01HA2G716KS9YGAGVY1WBVFJ8Y.pdf
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.
When making a generational ship, for safety we'd still want to do years of testing on orbit to see whether a chosen ecological system really does form a closed loop. Water recycling on the ISS is 98% efficient according to NASA, so with refuelings from ice moons every couple decades (solar system hopping) that should be covered. Ion engines are apparently also a thing (still sounds like science fiction to me, but they've been in production on space missions for a long time apparently!), I don't know what kind of longevity those have though, or whether refueling is realistic (might requires landers with expansive equipment for refinement of elements). Things like floor space, the way that I see it, that's a matter of cost more than a matter of ability, so having enough privacy so you don't kill each other is within our current tech level – again, iff we'd really care to do this. Hence I'd say we can do this nearly today, and then it also doesn't matter much if you need 400 years for 4ly or 12'400 years for 124ly.
On the other hand, by 10k years from now, I would think we can make a 0.9c human-sustaining craft, so maybe you're right that we'd rather choose to wait a thousand years and see where things stand then rather than putting effort into launching a generational ship next century, whereas with a 4ly target the generational ship is much more likely to be faster. Maybe you're right that this distance difference does matter. Not for ability so much as for psychological "would we spend that effort given the perspectives" reasons
Huh? Where did you get this idea? Our physics is clearly nowhere near complete. Quantum Mechanics and General Relativity are at odds, which is why physicists have been looking for a unified theory for ages. Each one only works at certain scales, and not at the other end, so obviously something's wrong with them. The whole "dark matter" thing looks like BS too, and alternate theories like MOND don't require it. There's nothing complete at all about our understanding of physics.
I’m not sure this is the case. Basically every physicist I’ve met thinks we’re in for another general relativity and that a unified theory will be a lot different than the multitude of theories we have now
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)Since 1984 is becoming a reality, Aasimov's works also have terrifying parallels with our current society... Just look at what happens with atom reactors in real life and the same is outlined in aasimov's works. Plus everything is sugar coated with religious bullshit, that only few can see through.
>When it comes to direct evidence of an industrial civilization—things like cities, factories, and roads—the geologic record doesn’t go back past what’s called the Quaternary period 2.6 million years ago. For example, the oldest large-scale stretch of ancient surface lies in the Negev Desert. It’s “just” 1.8 million years old—older surfaces are mostly visible in cross section via something like a cliff face or rock cuts.
While I think its highly unlikely (I mean less than 0.00001% possible) the means in which we would could even detect it are complicated
[0]: https://www.theatlantic.com/science/archive/2018/04/are-we-e...
I thought the Cambrian Explosion's fossil record was pretty sizeable - in fact, it's named after the place where the fossil layer was first discovered. I didn't know it was related to a common ancestor. Are you thinking of something else or am I missing something major?
>>> Complex animal life took 3.5 bn years to emerge on Earth,
>> How certain are we it took that long (the first time)?
> Not certain at all, it’s based on last universal common ancestor estimates(LUCA) and supported by (lack of) fossil record.
Do you mean, there's little evidence of pre-Cambrian absence? Absence of evidence is some evidence of absence, in this case.
But how does LUCA fit into this question?
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.
I.e. air-breathing aircraft + chemical rockets would work, as would other exotic solutions
Another way of looking at it—on a body with no atmosphere, the most efficient way to attain orbit is to be on the equator, point your spacecraft "east" (prograde to rotation), and elevate the nose just enough to avoid lithobraking on that mountain in the distance. If Earth were such a beast it would take roughly 7000 m/s delta-V to do this. IRL, because you need to get over the atmosphere first, it takes about 9000; the "gravity turn" is a compromise between losing energy to gravity/steering versus losing it to drag. So any exotic system—air launching a Saturn V is definitely exotic!—would help with efficiency, but I don't see that it would radically alter the situation.
I'm genuinely curious
See also: https://www.scientificamerican.com/article/could-an-industri...
Seeing that response and then your username
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
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.
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.
In summary, as you said, the altitude is less important than the base velocity increase and atmospheric density reduction.
The former, because you're pushing maximum mass at t=0 (i.e. all the future fuel you need to burn), so any added velocity at rocket ignition time would compound throughout the rest of the burn cycle (or, to think of it another way, you've already overcome fully-fueled vehicle inertia with the benefit of atmospheric oxygen combustion).
Similar to how a multistage vehicle operates more efficiently, albeit without the benefit of atmospheric oxygen.
The latter, because you're essentially getting atmospheric density reduction for "free" (in terms of saving your on-vehicle propellant), and your propellant efficiency (in terms of propellant:velocity increase) scales better.
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.
https://www.nationalgeographic.com/science/article/interstel...
https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.10...
https://ntrs.nasa.gov/api/citations/20200001904/downloads/20...
>our best chemical rockets are more like 450 seconds
If we're talking about leaving the Solar system, and 1G rockets, why on Earth would you ever even think about primitive chemical rockets? Obviously, nuclear rockets are a mandatory first-step before getting close to that level of technology.
And given that we already have nuclear power plants, as well as designs (untested) for nuclear rockets, why even bring up chemical rockets?