Incredibly exciting that these techniques for exoplanet spectroscopy have come so far so quickly. I have full faith that we will discover indirect chemical evidence of extraterrestrial life within the next 10 years. Once JWST [0] comes online it's going to be just a matter of time.
Please don't say stuff like "I have full faith" when it comes to astrobiology :(. It's really tough for us to even get funding for a lot of these missions, especially now that NASA is being pushed away from astronomy/science and into crewed spaceflight, and the added pressure of some people's "full faith" is really not helpful, as well-intentioned as it may be.
It's not clear to me inteleng is objecting to any possible religious connotations, so much as saying that astrobiology's success is far from assured and that much work needs to be done to prevent progress from being derailed.
Don't you think Astrobiology is reliant on peoples faith that interesting results will follow from the capital investments required? I think thats one of the main things that are pushing astrobiology forward. If no one gave a fuck, or no one had any faith in the field, there would be no capital investments. I honestly don't understand the sentiment in the comment - or why you would caution against having faith?
What would that indirect chemical evidence look like? Perhaps an example you have in mind? Outside of non-committal elements like Uranium or something showing up, I'm not sure what that evidence would look like?
No, but in keeping with the "earth-like" avenue of search... If there are other similarities to earth's chemistry (like having water), and we know earth's oxygen comes from breathing... Not evidence, but a good enough reason to look for some. How that happens, idk.
Yeah O2 is an input of cellular respiration. The presence of O2 is more likely an indicator of plant-life than it is an indicator of animal life. But plant life is still life.
You do not need animals to have plants. Plants came before animals here on earth. But I’m not sure of a way for animals to exist without plants. So yeah a stronger indicator of photosynthesis than cellular respiration.
Methane. It is only really transiently generated by geological means and decays quickly when exposed to cosmic radiation. It is also very likely made by any carbon based life ecosystem.
The absence of evidence is not evidence of absence, and so on. We don't know for sure there isn't life on Titan; we just haven't seen enough evidence yet.
It will be very tough with JWST. Many of the biosignatures are small features, and not so easily detected. There's only a handful of planets for which this might be close to possible.
From lightyears away, probably nothing except maybe a slight drop in the sun's output if the Earth happens to pass in front of it and a periodic wobble of the sun's location as the sun and Earth orbit the center of gravity of the sun-Earth system.
The Earth is pretty small and far from the sun compared to the kinds of exoplanets we've been able to detect, so the wobble (which might be detectable via doppler shift of light from certain elements in the sun) would be slight and probably hard to detect without some pretty sophisticated instruments.
It might be possible to detect something the size of the Earth from several light years away with a good enough telescope, but I'm not sure what the limit of that is.
Everything you say is true, but we are farther along than your comment indicates.
With a 6.5 meter space telescope and a star shade, we pretty much have the capability within just a few years to blot out the direct light from the host star and perform spectral characterization of exo-Earths using the light from their host star that is bouncing off of them. In particular, this is a direct exoplanet observation, not indirect like the host-star radial velocity method. An example being studied right now is HabEx (https://en.m.wikipedia.org/wiki/Habitable_Exoplanet_Imaging_...).
From such spectra, we can use chemical and general circulation models to constrain the atmospheric composition, height, and temperature. We can investigate whether the atmosphere is in chemical equilibrium, or if there is some non-chemical process active. The paper referenced in the article actually does some of this (although this is a larger planet).
They are a "hm, that's interesting" kind of a signal. They simply mean that a simplistic chemical view of the atmosphere does not explain the observation. It could mean the presence of life, or it could mean some other unknown, inorganic process.
See for example the Viking experiments: they detected signs of life on Mars, only to be disproved later by better understanding of soil chemistry.
If we are so small as compared to our sun, and these exoplanets may be so much larger - and we have the idea of a “habitable zone” for planets: is there a “habitable gravity” level for planet size that we should consider for harboring life?
Question, given the sun's wobble would result from rotating around the solar system's center of gravity, how feasible is it to actually know with certainty what the solar system is made up of?
Composition analysis is usually done using spectroscopy, which looks for the characteristic wavelengths of compounds that show up when analyzing spectra.
I was answering your question in a roundabout way: usually "wobble" gives very little information about the chemical composition of an exoplanet (other than maybe that it's a large gas giant).
I see. I actually thought your comment might have been said in bad faith as an insult, but I now think it was focused on the context of the post, while mines was focused on the context of what I was replying to. I was replying to the aforementioned method of detecting planets via dopplar shifts in a star's light... I've always wondered about that--with how much precision can you actually know what is causing the shifts. How many gas giants, smaller planets, etc? For example, I suppose two planets of equal size, orbital plane, and 180 degrees from one another would mute their gravitational effect on their host star.
> For example, I suppose two planets of equal size, orbital plane, and 180 degrees from one another would mute their gravitational effect on their host star.
Such orbits are extremely rare. Any such orbit would be highly unstable, as any perturbation would cause the planet to deviate from its location. (Strictly speaking, there are five points where objects can have an orbit that matches that of another planet. They're called the Lagrangian points, and the only ones that are stable are L4 and L5, 60˚ ahead and behind the planet in its orbit.)
From the wobble you can determine the approximate mass of the planet and how long it takes to orbit it's sun. I suppose you might be able to deduce some things about the shape of its orbit as well.
Knowing what a planet is made of would require some other technique. I think the best you could do from looking at the wobble would be to say things like "planets that orbit stars like this and having a mass of such and such with an orbital period of so many days are likely to be made of the same things that other planets with those characteristics are made of".
On the other hand, we can know pretty easily quite a lot about what it's host star is made of by examining the light it emits.
I suppose two Jupiters on the same orbital plane, 180 degrees from each other, would cancel out? Is it possible for observers to really know we have 4 rocky planets, 4 gas giants, and what their mass is, etc? Or, with what degree of certainty could this be known, and from what distance?
I don't believe you can have 2 planets in the same orbit, and once they're in different orbits they'll take a different amount of time to orbit; so you should be able to get individual measurements.
Edit: Well, as per the simulated stable thread, apparently you can have Trojan etc pairs of planets in the same orbit. Interesting.
There's possible and there's likely to happen in nature. two opposing planets in symmetry you'd have to have symmetric mass all around to cancel the forces out. One side will have the galactic centre on and the other won't might even be enough of a tiny imbalance to disrupt the orbits as you say.
If we can detect wobble, can we detect composition? (If someone observing us was more advanced, if they can detect wobble they can probably deduce composition?)
Not a dumb question at all NASA pointed the Galileo Satellite at earth during one of its flyby to see if they could detect life via the techniques they would like to apply to extrasolar planets:
That's exactly what I was wondering! It's such an odd choice to compare it to as I'm having trouble finding an exact number. This article mentions that it's a small amount of ice but not exactly helpful for a scale: https://www.universetoday.com/15374/is-there-water-on-saturn...
So there's little water on Saturn! but wait, since Saturn is about 300 times the size of earth, and Earth's mass is just 1/4000th water, I'm still utterly confused as how much it is compared to us.
What blows my mind is that Saturn in that image looks almost exactly like it does in the intro to Star Trek The Next Generation, which I always chalked up as bad CGI.
It's hard to measure absolute water abundances (it requires a lot of assumptions and extrapolating). This is a relative comparison of atmospheric water. We don't have relative water abundances for a lot of planets, so it's on the higher end, but we don't really know (maybe some other planets' water are hidden behind clouds).
That makes me think it’s a pretty substantive amount of water. If we’re getting 3x the spike we see for a planet in our own solar system in a planet lys away then actual content should be much more (due to signal/noise? Just guessing though)
That sounds... less than accurate. Will a sponge float in water? It's less dense...
I'm trying to imagine how the result of a close encounter between Saturn and a Saturn-sized bathtub full of water could be anything other than a single merged sphere with a lot of water content.
Right, and Saturn is less dense than water because it is mostly composed of air. It's like a sponge with the spongy lattice removed. It's not a solid. (At least, the vast majority of it by volume is not a solid.) That's why it's called a "gas giant".
I was going to say that it would be a star, but apparently (making an assumption about the mass of the saturn-sized bathtub full of water here) it would still be orders of magnitude from ignition.
An Olympic swimming pool scaled for a Saturn-sized swimmer on the other hand... Ignition!
You’d need on the order of hundred times the mass of Saturn to create a red dwarf, so the swimming pool might actually be enough to kick it into being a Sun-sized or even larger star.
And only 700 light years away ;) It would be nice to compare the atmospheric spectrum of WASP-39b. As well as other candidate exoplanets in habitable zones. With the baseline of our own home planet.
High resolution transmission spectrum of the Earth's atmosphere -- Seeing Earth as an exoplanet using a lunar eclipse
Just out of curiosity, what's the reason for looking so far out? Are we assuming by the time we would actually need to visit these planets, we've discovered some method to go faster than the speed of light? I only ask because realistically, how do we expect to actually make use of these resources if it would take so long just to reach it?
Learning about far-away planets is useful if we want to know more about planets in general, such as how do they form and what kinds of planetary systems are we most likely to find outside our solar system?
Even if we never visit that particular planet, we may learn something useful that tells us something about planets nearby, or even about our own solar system.
At this point, we're just collecting data about extra-solar planets, which we weren't sure even existed until recently. With so many unknowns, it's exciting whenever we can fill in our knowledge gaps just a little bit.
I believe the end goal is some proof of extraterrestrial life. As sensing becomes more accurate, we may be able to detect certain biochemical signatures. Even of a hypothetical alien variety. At even great distances.
Its an answer to the age old existential dilemma: are we alone in the cosmos. And would indeed provide a modicum of hope for the future of humanity ;)
The speed of light is not a speed limit on effective travel, but on observation. Imagine you build an engine that gives enough thrust to roughly produce an extra effective 1km/s of velocity each time you operate it. Even though the speed of light is 300km/s, that engine is going to operate exactly the same on the 301st operation as it did on the first operation. And, in fact, in 'real' terms if we create an engine capable of generating 1g of thrust for years at a time - we could travel 700 light years in ~12 years by thrusting for 1g forward 6 years, turning around and then thrusting for 6 years backwards.
But of course the 'catch' is that time dilation (and length contraction) kick in. And so while from the frame of reference of the ship and all its travelers only 12 years will have passed, from the frame of reference of everybody back on Earth - 700 years would have passed. What we would observe is that as the ship approached the speed of light, its apparent mass would approach infinity, reaching a velocity asymptote at the speed of light.
And these values are also not linear. It's possible to travel a practically unlimited distance in the span of a single human lifetime - from the perspective of that human. 100 trillion light years would take about 62 years at 1g from the perspective of those on board our ship. There's also really really fun paradoxes available here. Imagine somebody leaves Earth towards this planet and at some point decades, or perhaps even centuries later, we develop technology that enables substantially faster travel. Our planetary settlers on their 12 year journey could arrive 12 years later to find that not only is the planet indeed colonized, but it's colonized by the descendents of Earthlings that left decades, or even centuries, after they did.
The really exciting thing here is that NASA seems to have gone silent on the EM drive after having it pass every single test they threw at it. In my opinion, this is evidence of classification which is something that would make sense. If the EM drive somehow actually works - and everything we know says it most certainly should not - that would change absolutely everything. The ability to actually start realistically considering these sort of missions would be mundane compared to other possibilities, which I'm not even going to get into as they sound, and should be, absurd. As an aside, this part on the EM drive is 100% speculation - not to be confused with everything stated above, which are direct and heavily tested (even if absurd sounding) consequences of relativity.
> The speed of light is not a speed limit on effective travel, but on observation.
It is absolutely a limit on effective travel (if we ignore things like wormholes for a second). Conventional motion through space is bounded by c for several reasons, not the least of which being that the closer you get to c, the more energy it takes to make smaller and smaller changes in velocity (the object acts as though it's gaining mass the faster it goes). In fact, it's asymptotic. Accelerating a particle to c would require an infinite amount of energy.
This is a common misunderstanding, and was the point of the example. A stationary observer observing a particle being accelerated towards the speed of light would observe that particles apparent mass begin to approach infinity as its observed velocity approached the speed of light, thus requiring an amount of energy approaching infinity to continue to accelerate it further. However, this has nothing to do with the scenario with you being that particle.
You are currently moving at near the speed of light relative to many things at this very moment, yet your mass is certainly not approaching infinity, America notwithstanding! And if you accelerated enough in the opposite direction of your relative partner to exceed the speed of light it's not like you'd suddenly start finding it impossible. No, it's a matter of observation. From the other particle's perspective it would see your mass approaching infinity and your speed would slow, but the distances you covered would remain the same due to length contraction.
A similar effect explains why, for instance, particles in CERN's reactors travel distances that should be impossible for them to travel before decaying. E.g. if the speed of light was 10m/s and a particle decays after 3 seconds then it should be impossible to see that particle travel more than 30 meters. Yet we see it travel hundreds of meters. Isn't relativity fun?
Under relativity, you can't simply add speeds like that, unfortunately (I believe this is related to the fact that the speed of light is the same in all reference frames). Here's a link that can explain it better, though: http://curious.astro.cornell.edu/about-us/139-physics/the-th...
In short, you can't go faster than light in any reference frame, relative to any other observer.
Absolutely. You are not understanding what you are reading. Let's differentiate between 'mover' and 'observer' for clarity. In reality they're completely interchangeable as being at rest relative to something moving 10m/s is the same as you moving 10m/s if we consider the other particle to be at rest.
As you accelerate more and more you will never observe yourself or anything else exceeding the speed of light. Instead what will happen is that time will begin to slow down and distances will begin to contract. If in our frame of reference a distance is 100 meters, it would begin to seem to be, for instance, 10 meters.
And the people observing you will also never see you exceed the speed of light. Instead they will see you approach it, and then start to level off asymptotically. Both views are correct. Time itself is what changes. From the perspective of the observer, time will be moving more slowly for the observed. e.g. this is why particles at CERN travel vastly greater distances than they 'should' be able to before decaying. Imagine what it would be like to experience that travel from the particle's perspective.
This is why we see our particle last much longer than it should. And if humans could live for 1500 years, this is why we would see things like our ship make it's 700 light year journey, and then beam back a message that would only hit us 1400 years later - telling us that they're safe and sound and got there in 12 years. Quite fun stuff!
Put another way, this would be the timeline of our ship in years from its perspective and from earth's perspective:
0 earth relative = ship leaves
0 ship relative = ship leaves
700 earth relative = ship arrives at planet
12 ship relative = ship arrives at planet
1400 earth relative = message from ship on planet arrives at earth
712 ship relative = message from ship on planet arrives at earth
One final clarification, which might be unclear from the above. The ship obviously does not magically warp through time or anything like that. If there was a clock on the planet that started at T=0 when that ship left Earth, it would read T=700 years when that ship arrived since that planet is itself also roughly at rest relative to the ship.
This is the most counter intuitive thing about relativity, and time dilation. It's not some 'trick' or matter of perspective. Time itself does literally move at different rates for different people in different scenarios, even when we're all in the same universe. Our ship pilot could make the 12 year journey back and indeed 1400 Earth years would have passed in the interim, and if was somehow able to measure the age of the other planet - 1400 years would have also passed there as well. Even though he himself had only aged 24 years.
Should we achieve the ability to reach relativistic rates of travel - some people may get their wish. Expect huge chunks of the rich to up and leave 'to the future' (from our perspective we'd just see them constantly zipping around near the speed of light... for centuries) in hopes of discovering if humanity has overcome mortality by then! Reality is much stranger than fiction.
" According to special relativity, c is the maximum speed at which all conventional matter and hence all known forms of information in the universe can travel. "
Sure, that’s all true, but you still haven’t shown that anything can go faster than the speed of light. Time dilation and length contraction conspire to cheat you from doing this.
Did you read what TangoTrotFox wrote? At no point did he invoke any faster-than-light travel. He's just saying that by traveling at relativistic speeds (e.g. 0.99c <= v < 1c), time dilation / length contraction work in your favor. You can travel to systems thousands of light years away from Earth in only a few years (as perceived by you, on your spaceship), all while traveling a bit slower than light itself. Everyone left on Earth will still perceive you taking >1000 years to arrive.
I did, but it was a long post on mobile so I misunderstood their intent. I though that TangoTrotFox was disagreeing with tachyoff, when in fact he was just providing a better explanation.
No, it's correct - but speaking of physics on pop forums is pointless, because of the Dunning Kruger effect.
There tend to be three groups of people:
- Those that accept things at face value, which is quite silly. What I'm saying should challenge all intuitive notions of reality making open acceptance simply bizarre.
- Those that reject things at face value. No better than the first and generally driven by an extremely superficial understanding of physics. As Feynman phrased it, people sipping martinis at a cocktail party and discussing relativity, "Ah yes.. how insightful. Though I think some things may indeed be inherently correct. Mmm..."
- And those with a strong physics background already, to whom you provide no additional value to anyhow.
Since we're speaking of planets light years away. The only way for humans to get out there, is to stay in some kind of spaceship with gravity.
Floating around on the International Space Station is nice for an hour. But after that, I bet it gets boring real quick. Especially, if you need to go use the restroom, and handle liquids and solids.
So, having artificial gravity is nice. It will keep liquids down. You can drink out of a cup. Food doesn't float away. You can surgically operate safely. You can use the restroom normally.
But, you would need a very large structure, to spin around, in order to not get the effects of Coriolis Force. And since it is currently difficult to build such a large structure in space, then I wondered if we could cheat.
The method is to apply a constant force, but at an angle. This angle will allow the space craft to simulate a rotation, like it is being spun around with an invisible tether. This angular force will push all the occupants inside, to feel 1 G of gravity. And after one full rotation, then the space craft will return to the origin point.
So, the idea is to apply an angular force, to cause a space craft to rotate in place, to simulate artificial gravity.
This is similar to the idea of constantly accelerating a spacecraft, so that the occupants feel 1 G of gravity. But that acceleration would shoot the occupants straight into deep space, which is not what we want.
Instead, this method would be like simulating a Ring World, but instead of rotating the space station, it would use constant angular force to cause the rotation, in order to simulate the artificial gravity.
I was thinking something like an electric-ion engine could be used to provide the constant thrust. It would need to be computer controlled, to automatically administer the right force, at the correct angle, at the correct time, in order to rotate and simulate the artificial gravity. And it can be powered by nuclear, or possible solar. And of course, the thrust can never be turned off, otherwise, the space craft would shoot off into deep space.
One idea I thought was to have this be in a large orbit around the earth. The other location would be at the Earth-Moon Lagrangian Point.
Any space infrastructure architects want to take a stab at this idea? Possible or not?
You should watch The Expanse, a very good TV show.
Their ships accelerate at a comfortable level to generate gravity for half of the destination, and then "flip-and-burn" by accelerating in the opposite direction at the same comfortable level to generate gravity.
That only works inside the solar system. The energy requirements to accelerate for a year are enormous. With 100% efficient engines, you would need something like a reaction mass the size of Jupiter.
On the plus side you quickly approach c. At constant 1g acceleration / deceleration, Andromeda is about 28 years away.
Right, the people onboard the spaceship will only perceive 28y to have gone by. People on Earth will perceive the spaceship accelerating away for millions of years.
The ISS weighs 440t and to get 1g there by acceleration you'd need to constantly apply a force of ~4.4MN (meganewton), that's a tenth of a Saturn 5 at lift-off.
Not sure we can do that for an extended amount of time (read: a few hours) without bringing along lots of fuel
That or we invent that special drive of that dead Martian.
Ultimately, gravity is a relatively small problem in terms of interstellar travel. It's an implementation detail, so to speak. The main problem is that there is no energy in space.
> About 1 atom per cm³ and enough photons to read by.
Do you have a citation (or better yet, a calculation) for this? I’ve been searching for about 10 minutes and and it doesn’t quite make sense.
The full moon typically casts about 0.05 - 0.1 lx.[1] With perseverence and some eye strain, I think I could read by that on a particularly clear night. This isn’t a perfect heuristic, but it seems reasonable to start with as a baseline.
Per this calculation[2], 1 lx is approximatly equal to 5 x 10^15 photons per second per square meter. The best moonlight you can typically expect from a full moon is approximately a tenth of this luminosity.
Then per the notes here[3], there are only something like 450 photons per cubic cm in space on average, which seems reasonable for a first approximation of diffused light in interstellar space. That’s vastly lower than 0.1 lx, and that’s before considering that the majority of those photons aren’t actually visible light.
Sorry it doesn’t work. The correct force angle is always directly inwards towards the center of the circle the craft is tracing, and that force would need to be 1 G. Think of it as swinging a ball on a string—the ball is the craft, and the force on the string is your thrust force.
If you can generate 1 G of force (which is far beyond the capabilities of an ion engine), you’d be better off accelerating directly toward your destination and doing the “flip and burn” half way.
What is max velocity we can, with current tech, achieve for shooting a probe to a target;
Possible to build a giant rail gun in space where a falcon heavy is the payload (plus a nuke battery) and we shoot the falcon heavy out the rail gun, then at some point it’s various components engage to keep it heading to target.
Also if you shoot a rocket out a rail gun, and it’s clipping along, will the rocket thrust add any velocity, or should you save all that fuel to land the heavy on the remote planet?
The position of the Planet will not be the same when the "Projectile" will arrive. The Railgun must aim to the Destination the Planet will be. Fault tolerance will be a bigger issue than building a giant Railgun (Walmart maybe has one in stock already :P).
If you build a ship that accelerates at a constant 1g towards the destination until the midway point, then decelerates at a constant 1g, due to time dilation, the people on board would experience "only" 12 years passing for a 700LY journey. People on Earth would still need to wait 1400 years for the first communication back, of course, but at least you won't have to build generation ships.
The thing is, we aren't currently able to keep a stable acceleration of 1g.
The ship's mass will also increase relativistic-ally, as it will reach a maximum speed of ~0.9999961c, so more mass will require more force for the same acceleration.
...and according to that calculator, at 2gs it would take just over 7 years in the ship's frame of reference; at 3gs, slightly less than 5.
If you really want to get things over with quick, 10gs will get you there in well under 2 years. I wonder if that's survivable, if you were under water the whole time with a scuba tank or something?
The key to space is genetics. If we can master modifying our own code, we can solve all of the uncomfortable aspects of space travel (radiation, low/zero gravity, habitable environments※).
With extreme longevity you can even get over the time aspects (If a human can live for multiple centuries, a few decades spent on travel isn't that much time).
※ No need to terraform - instead of adapting the planet to humans, adapt humans to the planet. Scarce atmosphere? Add the Nepalese genes to survive at high altitude[1]. Heavy gravity? Increase bone and muscle mass. Water world? Gills it is!
The paper link is worth following if you're interested.
It describes using an exoplanet general circulation model (atmosphere model) to recover the temperature-vs-pressure profile within the exoplanet atmosphere - pressure being a proxy for height (Fig. 11a). They also retrieve temperature-vs-longitude.
> In 2014, the Israeli facilities of Hadera, Palmahim, Ashkelon, and Sorek were desalinizing water for less than US$0.40 per cubic meter. As of 2006, Singapore was desalinating water for US$0.49 per cubic meter.
Try drinking a thousand liters of water, and get back to me with how much you think it would be possible to spend this way before killing yourself through excessive water consumption.
I live in upstate NY, and $0.40 per cubic meter appears to be somewhat cheaper than my water bill. Although, that could be a wholesale price, without various overheads and fees.
In any case, it sounds like a few dollars a month for normal usage.
https://en.wikipedia.org/wiki/James_Webb_Space_Telescope [0]