Naked Science Forum
Non Life Sciences => Technology => Topic started by: Kryptid on 16/09/2013 03:40:27
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If humanity wished to let the other (so far hypothetical) denizens of the Universe know that the Solar System is inhabited by a technological species, what would be one or more good ways to do it? I realize that we intentionally broadcast signals into space for this purpose, but I feel that it's a bit of a shot in the dark. The Universe is so enormous that the likelihood of any intelligent civilization intercepting a directional signal seems fairly remote. I know that we can aim the signals at stars which we know have planets, but that's fairly chancy as we have no idea if those systems have intelligent life or not. I would prefer some kind of spherical broadcasting system which sends signals in all directions at once, but that seems rather energy-intensive.
I realize that many of you might say that we have already been broadcasting radio waves spherically for decades due to television signals and the like, but according to this article: http://zidbits.com/2011/07/how-far-have-radio-signals-traveled-from-earth/ (http://zidbits.com/2011/07/how-far-have-radio-signals-traveled-from-earth/), those passive signals would have degraded in strength to such an extent that they would be practically indistinguishable from background radio noise after only travelling a few lightyears (the closest star, Proxima Centauri is more than 4 lightyears away).
One idea I had would be to cover several large asteroids with a collection of highly reflective mirrors. Dope the mirror with some kind of artificial impurity or pigment so that any civilization detecting the sunlight reflected off of them could tell from spectrum analysis that it was composed of something that is not naturally-occuring. Being covered in such a highly-reflective material should also make the albedo of the asteroids unnaturally high, making it even more suggestive that they were altered. What's more, the fact that they simply reflect light from the Sun means that it would be a passive system not requiring any artificial power input.
Obviously, even mirror-coated asteroids would be extremely dim when compared to the light from the Sun. I doubt with our current technology that we would be able detect any such similarly-altered asteroids around other stars. However, a very advanced civilization may be able to detect such asteroids with little effort. Also, if we could alter enough asteroids to be reflective then the combined effect of hundreds of them might work towards making them more detectable. I realize doing something like this isn't practical with current technology, but I don't consider it outside the realm of possibility for us to produce robotic landers that could fly to the asteroids and construct the mirrors from the raw materials present there within a century. No need for astronauts to waste time flying there. I'm sure there would still be a fat price tag for this project, however...
Take note that this isn't about whether it's a good idea to let aliens know about us or not, it's just an exercise to see what might be done if we really wanted to let them know of us.
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This is an interesting question because it has two aspects: how to make a signal distinguishable from noise at a great distance, and how to signify an intelligence behind it. It's certainly about intelligence and engineering, and if those subjects aren't in the exclusive province of science, I don't know what is!
A spectacular one-off, like blowing Mars apart with a big bomb, might just be noticeable to anyone who happened to be studying our tiny little solar system in 5 or 10 years' time and again a week later, but whilst it would be an intriguing finding, it might equally have been caused by asteroid impact or internal volcanic activity- far more probable than the evolution of a life form both powerful enough and stupid enough to advertise itself.
To maximise the probability of detection, the signal has to be quasicontinuous. The WOW signal http://en.wikipedia.org/wiki/Wow!_signal is the best-known example of an incoming phenomenon that might have had an intelligent source but although it met a consensus of criteria regarding its duration and frequency, and could conceivably have originated from an artificial transmitter, it hasn't been heard again.
But not too continuous! Pulsars and geysers produce very regular signals from unintelligent phenomena. You need to add some variation that looks too random to be mechanical but not so random as to be noise. The idea of repeating a standard header followed by an increasingly time-variant message lends authority, as in "here is the BBC 9-o'clock news....here is the BBC 10-o'clock news....."
According to Wiki, the WOW transmitter required a few gigawatts: way beyond human capability at the time it was received but not, I feel, beyond the potential of a pulsed laser with its own power station. Maybe we should go for it. Or maybe not!
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When I were a lad I remember reading a science fiction story about humanity exploding an atomic-bomb, 50 MT I believe, in order to map the solar system. This got picked up by an alien race some light-years distant who did the same thing thus telling us of their presence. Today I imagine a 50 MT bang in space would not be considered as anything special. However, since then we have developed bombs that are designed to expend more energy in EMP rather than blast. Take a handfull of such nasties and fire them off into space separated by 1,3,5,7 and 11 days and the signal would show that we are intelligent and give information on the length of our day (and the efficiency of our weapons. Ouch.).
If it is possible to manufacture two versions of such bombs, each generating very different radio frequencies, we could even send very clear message that, yes, we do binary too.
Now we just sit back and wait.....
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Construct a large lens and set in orbit around the sun to act like the flash of a light house.
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Or make a small, wet planet that will be observed by alien astronomers, just as we are looking for theirs. The rest is just chemistry.
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If atmospheric oxygen is detectable from afar, then it would indicate the presence of life, and perhaps intelligent life would be inevitable.
A simple pen laser should travel for a very long distance. However, considering Earth's orbital velocity of about 30,000 km/s, shining a tiny spot at a planet orbiting a distant star, then the spot would travel across the planet surface too fast to be seen.
So, ideally one would focus one's communication beam to cover the cone, say from the star out to the equivalent of Jupiter.
Nonetheless, if we use a focused beam, and focused listening, then say we broadcast to each target star for 5 minutes a year, and listen for a reply from that star for 5 minutes a year. Say an alien race is doing the same, then the chance both will be broadcasting and listening at the same time is quite low.
Perhaps the WOW signal (http://en.wikipedia.org/wiki/Wow!_signal) was merely a short burst being sent out once a century in every direction, and we merely have to patiently wait for it to come back, and the sender would be expecting us to continually broadcast back in that direction.
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The beasties that live around thermal vents in the ocean floor don't use atmospheric oxygen, but all recognisable life forms use water.
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Life made the oxygen in our atmosphere, so an oxygen rich atmosphere would be indicative of the presence of life. Oxygen is very reactive, and one might not expect high levels of oxygen without life.
Water may be necessary for life as we know it, but there are many planets that have at least ice without having life, so seeing water would indicate that life is possible, but not that it exists.
Europa (http://en.wikipedia.org/wiki/Europa_(moon)) may well have liquid water oceans covered with a thick ice cap, and could potentially support terrestrial extremophiles. In the future, the hunt for life on the moon will tell us a lot about the potential for life on other planets.
- All planets that have water based life will have liquid water... somewhere (even with freeze/thaw patterns). but that may give a lot of false positives for "life".
- Only looking for atmospheric oxygen would have a much higher specificity, but may, however, miss some havens for life that could be much different than what we have on Earth (false negatives).
- And, of course, somewhere there may be life that it entirely different from what we can envision.
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According to Wiki, the WOW transmitter required a few gigawatts: way beyond human capability at the time it was received but not, I feel, beyond the potential of a pulsed laser with its own power station. Maybe we should go for it. Or maybe not!
The problem with a laser is that it would have to essentially be focused as big as the solar system to be noticed, and still only if targeted at exactly where the target star would be in a number of years when the signal would finally reach the destination.
Even with a conventional parabolic dish antenna, it should listen in the direction of where a star was when the signal would have been sent (actually, that is the direction we see the light, so listening towards the stars is ok). However, it should broadcast in the direction of where the star will be when the signal arrives. If one targets stars within 5 to 1000 light years, how much do they move relative to our movement? I assume the signal still gets hit by the Coriolis effect. I suppose it also depends on how tight the focus cone of the antenna is. Is there a star within 1000 light years distance within 1° everywhere one looks?
One method that surely would get noticed would be to put a 2 million km diameter louvered disk in orbit around our sun so that it totally obscures the sunlight, and could be designed to flash at a specific frequency as it passes in front of the sun. You could project the sunlight elsewhere if one desires. However it would primarily only be visible on the ecliptic, and might only be visible to some of the stars once every few million years. Of course, building such a beacon would be beyond our engineering capabilities.
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Methane (http://www.space.com/18339-mars-methane-alien-life.html), plenty of methane. Baked beans and sauerkraut, anyone?
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Titan (http://en.wikipedia.org/wiki/Titan_(moon)#Atmosphere), of course, is downright chilly, but also has an abundance of Methane in the atmosphere.
Obviously nobody has either proven or disproven the existence of life on Titan, but Methane seems to be a very non-specific marker for "life".
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How about making a small black hole and sending it into the sun.
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How about making a small black hole and sending it into the sun.
What? Turn the fire off? Might get a bit chilly. Hey somebody stick another log on the sun please.
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While Jupiter isn't supposed to be large enough to sustain fusion, what would happen if one detonated a large H-Bomb in Jupiter's upper atmosphere? Could one create a large flash of light? Of course, it wouldn't necessarily indicate intelligence, but might draw attention to our solar system. Would the flash be repeatable at a regular interval?
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While Jupiter isn't supposed to be large enough to sustain fusion, what would happen if one detonated a large H-Bomb in Jupiter's upper atmosphere? Could one create a large flash of light? Of course, it wouldn't necessarily indicate intelligence, but might draw attention to our solar system. Would the flash be repeatable at a regular interval?
If you were to set off a sequence in morse code over an extended interval it would show intelligence. Ten bombs detonated in sequence could be a dash, five could be a dot with a gap in between each signal. A good way to disarm countries with nuclear weapons and make the world safer. However the signalling might well bring something worse.
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Take a planet with abundant water an life (the Earth, for example) and heavily pollute the atmosphere with industrial particulates, sulphur, carbon dioxide, methane, CFCs, etc.
Spectroscopically, a dead giveaway for low-grade intelligent life...
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Inject large (very large) volumes of a specific element into the sun's atmosphere in order to change its spectroscopic signal. Vary the element and the duration to code your message.
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Inject large (very large) volumes of a specific element into the sun's atmosphere in order to change its spectroscopic signal. Vary the element and the duration to code your message.
Say you dropped Mercury into the sun.
The planet.
You'd add some iron and etc. But would it be enough to make the change detectable considering the mass differences between the sun and Mercury? Of course, depending on your method for dorbiting Mercury, you'd get a nice solar flare (hopefully not facing Earth).
It wouldn't be unexpected for a massive body to strike a star. So, as you mentioned, it must be repeated. I could imagine a lot of "mass" being used for relatively few signal transitions.
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I have not calculated what mass of material one might have to add in order to produce a recognizable spike in the spectrum. I'm not even sure how I would go about that. Although I said a large amount would be needed I suspect it would be many orders of magnitude less than planetary mass. (However that suspicion is based on nothing more than subconscious intution.) Perhaps there is something in the literature relating to cometary impacts that would yield a rough number.
Edit: So this paper is quite interesting and implies that with technology that aliens might plausibly have, they could detect emissions and flare events from cometary mass impacts. http://arxiv.org/pdf/1107.1857.pdf Please note the implication is mine and not that of the authors whose interest is soley with cometary impacts and sun grazers.
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NASA has sent a golden disc into space that has information of location of earth , if it cones to hands of alien then we could contact them .