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 more CH bonds before ultimately breaking down into methane again. Hence, an exoplanet with both molecules in its atmosphere is a promising candidate in the search for life.
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 Moon.
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.
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.
Note that 8 times more massive doesn’t mean it has 8 times surface g, unless it’s exactly the same radius as the Earth. If the planet is larger you’re further away from the center of gravity.
For example, the Earth is 10 times more massive than Mars, but only has 2.6 times surface g.
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.
As others have mentioned it wouldn't be 8 g. Life would be smaller. There would be speed differences. A lot of optimums and limits depend on how volume scales against area. Like the biggest terrestrial animals are limited a characteristic dimension (height or length) x being proportional to femur area x^2 being proportional to mass x^3. Mass grows proportional to x^3, femur strength (area) grows proportional to x^2, so you have a limit on how big a thing can be when you run out of available femur strength.
Higher gravity means this upper limit will be smaller. All sorts of similar scaling things will change optimum points for structural and energy reasons.
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.
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)
We know that it's not (primarily) rocky though because the radius is 2.6 that of earth, but the mass is only 8 times. So it's about about 46% as dense as earth.
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#....
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.
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.
I think an air-launched rocket would only be an incremental help. Chemical rockets on Earth are barely at 1/8th of orbital speed before they're out of most of the atmosphere (~60km altitude). You can't accelerate more without ascending because drag increases exponentially with velocity at a given air density.
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.
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.
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).
A true Bayesian I don’t think would use evidence for life on earth as the silver bullet for life elsewhere. They’d at least set up a model that considers all possible planets in the entire universe and test to see if these putative signatures even give you the power to identify earth as a life holding planet with confidence.
On this topic, I just finished reading "A Very Short Introduction to Planetary Systems"[0] by Raymond T. Pierrehumbert. He devotes a good portion of the book to exoplanet atmospheres. It is one of the best science books I've read. Pierrehumbert really has a knack for explaining complex material clearly and concisely. I really recommend it.
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, 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.
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).
[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.)
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.
Single cell life appeared on Earth almost instantly after the planet cooled down enough to allow it. I don't think it's clear that any progress was being made over the next few billion years. One day the right mutation happened and boom, fancy life everywhere. With our data sample of one, I don't think it's clear if it was extraordinarily bad luck it took that long to happen, or extraordinarily good luck it ever happened at all.
Eukaryotic cell is such a bonkers insane development, I definitely lean towards the impossibly lucky scenario. There was no need for that to be the origin story of a mitochondria like organelle (https://en.wikipedia.org/wiki/Symbiogenesis), but that's what we think we have.
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.
It not only has to work, the mutant has to have a fitness advantage over the nonmutant or it will drop out of the population before long. The vast majority of mutations are also “bad.”
The fossil record. There is little evidence of very complex animal life before about 541 million years ago, which is when the Cambrian explosion begun.
Before "modern" life evolved in the pre-cambrian era, there was the Ediacaran life forms that were complex multicellular life, but died out millions of years before the Cambrian explosion.
There's quite a few fossils showing single-celled organisms from 3+ billion years ago. I imagine if more complex life existed the fossils could've survived
Its possible there is a good explanation for why there would be no strong fossil record[0] for an advanced civilization preceding us.
>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
> it’s based on last universal common ancestor estimates(LUCA) and supported by (lack of) fossil record.
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?
I think we can see where different complex animals split in their evolutionary tree - so humans and starfish split a long way back. Then we use a standard mutation clock to estimate how long ago that was. If all complex animals split from simple animals an estimated 700m years ago...
Wow, that's really close so far as these things go. With the nearest star being 4ly, this can be reached with essentially the same tech level if we'd want to visit that with a rover or generational ship one day
We'd need some fast tech for sure. However, what is also interesting is that the light from it is only 124 years old. So the planet is still very similar today probably.
> this can be reached with essentially the same tech level
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.
Fair points. It's all guesses about the unforeseeable future, but I would estimate that a multigenerational ship is in arm's each if we really wanted to, whereas accelerating so much as an orbiter (let alone a lander, or a whole rover, or a live person) to 0.9c probably requires a tech level we don't have due to the fuel requirement for deceleration. Maybe a fly-by could work, then burst back the results with some enormous amount of energy, but that's a lot of cost for very little information.
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
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.
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.
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.
>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.
>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?
Dyson proposed a fusion pulse propulsion system in the 1960s that was estimated at 70000 isp. Maybe 1m wouldn’t have been that far off from the limits of these crafts if test ban treaties didn’t kill their development.
Would it melt before then? Interstellar space is extremely thin, on the order of 1 atom per cubic centimeter (estimates vary). But, as we learned when Voyager finally left the solar system a few years ago, it is hot as hell. More than 54,000 degrees F according to National Geographic:
The Voyagers didn't have today's ion engines. I don't know how much that gains us, though, as the main speed gain was by leeching momentum from planets' momenta, rather than from the hydrazine thrusters it carries
Orion drives can get up to some respectable fraction of the speed of light. Just need a billion or so 1-kiloton nukes. No biggy. No worries about sneaking up on them and startling them either.
For emission spectroscopy has been a thing since 1859 when Gustav Kirchhoff figured it out but for stellar emission spectroscopy it was Joseph von Fraunhofer in early 1800s? Although 1866, Pietro Angelo Secchi may have also discovered stellar emission spectroscopy 1848.
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 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.
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...
This is an easier problem than it probably seems. Atmospheres are relatively low-density gas, which means they produce an absorption spectrum - a chemical fingerprint that identifies most atoms and molecules quite reliably. It's such a good fingerprint that it was used to discover several chemical elements, most notably helium (observed in the Sun's spectrum before it was known on Earth).
> These initial Webb observations also provided a possible detection of a molecule called dimethyl sulfide (DMS). On Earth, this is only produced by life. The bulk of the DMS in Earth’s atmosphere is emitted from phytoplankton in marine environments.
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?
It is produced industrially without needing life. I’m not sure why its the alleged smoking gun if theoretically if the conditions are right and the reaction is catalyzed it will go on without needing a lifeform.
Yeah, not sure about the sensitivity, if it's particularly good conditions here but at least this data set looks like it gives remarkably little room for false positives and quite highly detailed. I thought it would push JWST a bit harder but this looks promising. Even a novice can read out the evidence for various molecules in that graph? So, if only we'd find an exciting result soon!
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...
The science clearly says FTL is possible: Einstein himself postulated wormholes (known now as Einstein-Rosen bridges), and warp drive has been proven to be possible (though not too practical yet) by Miguel Alcubierre and Sonny White.
There's no realistically plausible solution I've ever heard of, that is, ones that don't require millions of years of setup and entire stars worth of energy production. But that's with our current understanding of physics. While our current models seem nearly perfect and therefore nearly complete, there was a time they thought that about Newtonian physics. Perhaps some detail we need to understand dark matter or dark energy could spring the whole field wide open again.
>While our current models seem nearly perfect and therefore nearly complete
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.
> While our current models seem nearly perfect and therefore nearly complete
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
Not a lot of help for interstellar travel, but I believe that most of the mass in the visible universe is traveling away from us at faster than the speed of light.
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.
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.
Yeah, that, or advanced technology is suppressed and only a select (controlled) few can research it. And these phenomena are glimpses of what is possible, but not ready for global introduction.
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.
I picked up a random book in the science section of the city library today and opening it to a random page I started reading about an exciting "goldilocks" exoplanet discovery from 2015. Apparently this was the first exo-planet which had a positive spectroscopic identification of water in the atmosphere. It was a rocky world, 2 billion years old, 8 times Earth's size (mass?), on a 33 day orbit around a red dwarf. K-something-or-other. The book said the really exciting discoveries will happen when Webb comes online in 2021. The link is down, but someone mentions this planet is 8 x Earth size down thread. I wonder if it's the same planet?
Sorry, didn't notice the reply in a timely way. I went back to the library, the book was "The Universe" by Andrew Cohen. It was indeed K2-18B, discovered by Kepler in 2015. It says that the water was discovered by Hubble later, so presumably 2019.
Sorry, didn't notice this in a timely way. I went back to the library to check, and indeed the planet I was reading about was K2-18b. The book at least says that K2-18b is a Super-Earth and will almost certainly have a molten rocky core.
> "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?
What makes it feel like a big deal? Carbon, oxygen, and hydrogen are extremely abundant. Those molecules are relatively low energy combinations of the elements. I would be surprised to not find them in the atmospheres of big rocky planets.
Apperantly it seems to be the presence of " dimethyl sulfide ".
It seemingly only produced, on earth at least, by life. So using us as a baseline it seems pretty interesting.
> DMS is generated by the degradation of dimethylsulfoniopropionate, which is present in many species of marine algae and plants, including dinoflagellates and coccolithophores
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.
