THEY are coming.... What would *really* happen?

[1of6Billion]

Forget what you have seen in movies or on the History channel when it comes to Aliens visiting earth. Lets figure out how this would go, assuming they operate under our known laws of physics.

First: Detection

At a certain point their craft has to decellerate, so I assume detection will be of a crazy fast super hot object being detected at the outskirts of our solar system when they burn to decellerate. Who would detect that? How will this be explained away at first?

Lets pick it up from here. Any other toughts?

Please lets assume they are benevolent and 'we' show them our best side as well.. So no killing and/or enslaving. Ok?

[PlonioFludrasco]

Forget what you have seen in movies or on the History channel when it comes to Aliens visiting earth. Lets figure out how this would go, assuming they operate under our known laws of physics.

First: Detection

At a certain point their craft has to decellerate, so I assume detection will be of a crazy fast super hot object being detected at the outskirts of our solar system when they burn to decellerate. Who would detect that? How will this be explained away at first?

I think an x-ray or a gamma ray telescope first, because most likely they will use some kind of nuclear or quantum propulsion, appearing like a strange gamma burst.

Then, it could be tracked using IR (because a nuclear reactor is damn hot!!) and also a radio transmitter/reciever (like ones of the Deep Space Network) could be pointed at it to detect modulated signals (to be certain it's an artefact) at first and then estabilish some kind of communication.

[1of6Billion]

I think an x-ray or a gamma ray telescope first, because most likely they will use some kind of nuclear or quantum propulsion, appearing like a strange gamma burst.

Then, it could be tracked using IR (because a nuclear reactor is damn hot!!) and also a radio transmitter/reciever (like ones of the Deep Space Network) could be pointed at it to detect modulated signals (to be certain it's an artefact) at first and then estabilish some kind of communication.

Gamma burst. Nice. Is there some kind of omni directional detection going on?

I assume it will take some time before the scientific community accepts the idea it might be aliens.

[DeepOdyssey]

If they are looking for a new home, i would gladly gave them all seismic, atmospheric, climatic data on our solar system planets. Worse, if they are breathing oxygen/nitrogen mix, i guess we couldn't accommodate another billions of lives on our planet.

[magnemoe]

If we assume slower than light and braking, we would get all the shatter form the rocket doing the braking burn. This would include radio and visible light.

Guess it would be detected by systems looking for comets and asteroids however it would be easy to see that its something artificial and you would detect that its under trust after at least some days.

They might have braked against the interstellar gas to get down from relativistic speed, think bussard ramjet but you only use the field to push the gas, this would be hard to detect but would not be as effective at lower speeds.

First action would be to try to contact them by radio, perhaps also laser. Would be a bit surprising if they did not try to contact us to as they should be studying earth while approaching.

You would also start to analyze that you see, possible engine type, estimated weight of ship and so on.

[Moss]

What if they use something like a warp drive or a solar sail?

[magnemoe]

What if they use something like a warp drive or a solar sail?

Warp drive and we would not detect them before they exit warp and started to trust, solar sail, this would require laser boost and its an high chance we would detect the laser during boost (mote in the gods eye)

[Godot]

I´d expect a separate mothership (for interstellar/interplanetary travel) and atmospheric landing craft (probably with aerodynamic shapes and enough fuel to get down and back up again even in thicker atmospheres than ours) ... so I guess their mothership/s will remain in orbit, while they will just send in their landing craft to establish first contact.

Or maybe even try to establish first contact via radio comm, before going down, assuming they know that the planet harbors a civilization that is primitive, but yet developed enough to communicate via radio

[KerbMav]

Actually, if they are not really clever guys and deciphered our radio signals (should we even talk about TV?) and then even managed to interpret our hundreds of languages ...

[Scotius]

There will be about six hundred new religious sects popping up overnight. Each and every one will be claiming that their prophetised messiah is coming to take all righteous (members of their sect that is) to space Eden somewhere. In the mean time politicians will be bickering across the globe, military will be preparing for eventual invasion, conspiracy nuts will start rioting. And internet will explode from a gazillion new memes

[peadar1987]

And you'd have religious groups falling over themselves trying to claim that whatever beliefs the aliens hold backs uptheir position.

[Nuke]

we would detect a relativistic kill vehicle about 30 seconds before it hits us.

[Geschosskopf]

Forget what you have seen in movies or on the History channel when it comes to Aliens visiting earth. Lets figure out how this would go, assuming they operate under our known laws of physics.

First: Detection

At a certain point their craft has to decellerate, so I assume detection will be of a crazy fast super hot object being detected at the outskirts of our solar system when they burn to decellerate. Who would detect that? How will this be explained away at first?

Lets pick it up from here. Any other toughts?

Please lets assume they are benevolent and 'we' show them our best side as well.. So no killing and/or enslaving. Ok?

Let us assume the aliens have just sent a scout mission, not an invasion. I would thus expect their ship to be a small robotic probe using a solar sail. As such, it would have started its braking maneuver out in the Oort Cloud so would be going somewhat like a long-period or 1-and-done comet as it started to enter the actual planetary system. It would be rather reflective so we'd see it coming from a long way off, and it would be spotted fairly early on by some amateur comet-hunter. It would soon generate a lot of interest and professional observation because its brightness at that distance, and its huge size, would make everybody sit up and take notice. Then folks would figure out that it had absurdly small mass for its size, which would generate even more scientific interest, and it then wouldn't take long for folks to figure out it had to be a solar sail and therefore an alien ship.

So yup, there are aliens out there. No real surprise. And they don't have warp drive or any other super science stuff, but apparently are just mortals like us. They won't be bringing us new toys that will advance or civilization. They won't be taking us away in their mothership to some paradise we can't imagine. And they won't be invading us any time soon. Nope, they're just working-class slobs wondering what's out there. This will make the whole experience A) a lot easier to accept for most folks and rather anti-climactic. It'll be no different than knowing there are people who live on other continents here on Earth. So not a big life-altering event, really.

And there will be a lot of time for this realization to sink in. I doubt the alien ship would enter the solar system very near the ecliptic so it would have to make a major plane change maneuver to get anywhere near Earth (assuming it wanted to stop here instead of just pass through). Plus of course further braking maneuvers to capture and circularize. All this could well take decades or even centuries over several solar orbits with the 1st few going way back out into comet territory. All this before it would be in a position where we could send something out to meet it. So there'd be maybe several generations of Earthlings born knowing there was an alien ship up there in sky, and able to see at it with binoculars or even the naked eye at times, but to them it might as well be just another star for all the difference it makes to their daily lives. So by the time the thing finally gets reachable by a ship from Earth, we'll probably have forgotten about it .

[magnemoe]

Let us assume the aliens have just sent a scout mission, not an invasion. I would thus expect their ship to be a small robotic probe using a solar sail. As such, it would have started its braking maneuver out in the Oort Cloud so would be going somewhat like a long-period or 1-and-done comet as it started to enter the actual planetary system. It would be rather reflective so we'd see it coming from a long way off, and it would be spotted fairly early on by some amateur comet-hunter. It would soon generate a lot of interest and professional observation because its brightness at that distance, and its huge size, would make everybody sit up and take notice. Then folks would figure out that it had absurdly small mass for its size, which would generate even more scientific interest, and it then wouldn't take long for folks to figure out it had to be a solar sail and therefore an alien ship.

So yup, there are aliens out there. No real surprise. And they don't have warp drive or any other super science stuff, but apparently are just mortals like us. They won't be bringing us new toys that will advance or civilization. They won't be taking us away in their mothership to some paradise we can't imagine. And they won't be invading us any time soon. Nope, they're just working-class slobs wondering what's out there. This will make the whole experience A) a lot easier to accept for most folks and rather anti-climactic. It'll be no different than knowing there are people who live on other continents here on Earth. So not a big life-altering event, really.

And there will be a lot of time for this realization to sink in. I doubt the alien ship would enter the solar system very near the ecliptic so it would have to make a major plane change maneuver to get anywhere near Earth (assuming it wanted to stop here instead of just pass through). Plus of course further braking maneuvers to capture and circularize. All this could well take decades or even centuries over several solar orbits with the 1st few going way back out into comet territory. All this before it would be in a position where we could send something out to meet it. So there'd be maybe several generations of Earthlings born knowing there was an alien ship up there in sky, and able to see at it with binoculars or even the naked eye at times, but to them it might as well be just another star for all the difference it makes to their daily lives. So by the time the thing finally gets reachable by a ship from Earth, we'll probably have forgotten about it .

Plausible scenario, and yes they will be pretty close in technology with us, just 100-300 year ahead.

Assume the aliens are 30 light-year away, travel time 300 year, who would require 0.1 c, will a solar sail be able to brake from this speed? will it not require beamed power, my idea of braking against the interstellar gas also require power.

[Aghanim]

@magnemoe: A failed Bussard ramjet/magnetic sail/magnetic scoop could decelerate without sunlight, but I think that a solar sail could work too

Lets say they are using warp ship. They dropped out from warp in space between Jupiter and Saturn, because warp navigation isn't advanced enough. Assuming this is true,and assuming the radiation isn't planet threatening, when the ship is dropping out of warp, they will release a stream of gamma ray that our GRB satellite will detect. This will either create a lot of confusion, or it will create huge amount of suspicion that someone is doing nuclear testing in space. First option is more likely.

The more interesting question is: What do we do after they announces an alien spaceship is coming to us?

[Geschosskopf]

Plausible scenario, and yes they will be pretty close in technology with us, just 100-300 year ahead.

Assume the aliens are 30 light-year away, travel time 300 year, who would require 0.1 c, will a solar sail be able to brake from this speed? will it not require beamed power, my idea of braking against the interstellar gas also require power.

It all depends, but you could probably arrange the thing to slow down enough for capture without beamed power, depending on how you launched it.

In any case, the whole idea of doing interstellar trips with sublight ships is rather silly due to the time required. In the centuries it would take to get anywhere (not to mention slow back down and achieve orbit at an inner planet with very low-thrust means), the folks back home might have invented warp drive. If not, the information gained would be more akin to archaeology than communications.

I think it was Heinlein who wrote a story about some huge, multi-generation colony ship that had the usual exciting disasters and troubles to overcome en route. Finally, centuries after launch, it arrived at its destination. And there it found the ruins. Back on Earth, they'd invented warp drive and had gotten there long before, grown a colony from up from its founding population into a global civilization, and then it collapsed, all long before the sublight ship arrived.

Edited July 25, 2014 by Geschosskopf

[Mitchz95]

In any case, the whole idea of doing interstellar trips with sublight ships is rather silly due to the time required. In the centuries it would take to get anywhere (not to mention slow back down and achieve orbit at an inner planet with very low-thrust means), the folks back home might have invented warp drive. If not, the information gained would be more akin to archaeology than communications.

I think it was Heinlein who wrote a story about some huge, multi-generation colony ship that had the usual exciting disasters and troubles to overcome en route. Finally, centuries after launch, it arrived at its destination. And there it found the ruins. Back on Earth, they'd invented warp drive and had gotten there long before, grown a colony from up from its founding population into a global civilization, and then it collapsed, all long before the sublight ship arrived.

Yeah, I agree with this. If a ship design can't reach another system in less than fifty years, I think we should wait until technology catches up.

[Mazon Del]

First off, in a way it makes tactical sense in a first contact situation with a less technologically advanced race to make the other side think you are less powerful than you are. This is generally because if you seem to be their tech level, plus a couple decades, then they can draw conclusions about what you can do. And if you sent just a simple solar sail probe over then they can somewhat reasonably assume that you are incapable of landing an invasion force. As a result, they will likely take knowledge of your existence a little more calmly. Meanwhile of course, you are cloaked in orbit having gotten there in your warp drive (coming out on the backside of the moon to hide the gamma burst) and watching the news in real time, possibly even hacking their data systems with your quantum computers, to see how exactly it is that they are going to react. Once it looks like you can trust that they have peaceful intentions, then you let them know that in X number of years a peace envoy will be arriving. This ship would display better technology, but not enough to make them suspicious. Maybe you show off your nuclear drives fueled from comet water, etc. Old hat to you, but new to them. Just don't go too far or they will get suspicious. The meeting happens, you set things up and as you grow ties between the groups you slowly let them in on the technology. This is particularly useful because it keeps you ahead of them for a while, meaning that if you end up having any sort of interstellar trading going on (information or rare valuables), you end up with the better part of things. But you also get to seem generous, passing off old technologies to them, with them believing that you are willing to just hand over your bleeding edge technologies rather than guard them. Such generosity will tend to slowly color and influence relations between the groups favorably. Eventually they are up at your level, and you have been nothing but kind to them, which if you are a peaceful race, is probably what you wanted in the first place. Sure eventually they figure out what you did, but by that point they would likely see the logic in it.

Incidentally, this thread made me think of a new scifi book. It starts with some astronomers detecting the incoming solar sail ship. They figure out relatively quickly what it is given its tremendous speed, size, and low mass. So they try to talk to it. We end up getting a message back explaining the dire situation on board. Their original plan had been to have laser boosted acceleration into the system, then they would detach their first sail to use as a reflector for the laser beam, and use that to slow down. Only something went wrong, they have last communications with their home planet and the laser was no longer active. The sun will slow them down, but they are going too fast for that to keep them in the solar system. They can adjust their orbit to buy is several more months, but they need our help to survive as they do not have the resources for another interstellar journey. They transmit over schematics for a massive laser cannon, a copy of the one they used, and power plants. This thing is massive and in the time we have, nations have to come together to share the economic burden of making something so massive in such a short time period. The book of course would cover the political situation of nations jockeying over the choice bits of the systems construction. Who gets to keep the death ray (IE: Where is it built) etc. The social setup of this, people who believe we should build it vs people who don't. The devious plan by someone to retarget the laser system to blast the "invading" aliens rather than help them. All that jazz.

Incidentally in one series I read, after humans had invented warp drive, they went around to all the cryo-sleeper ships to wake everybody up and ask if they wanted a warp ship instead. There had been a large exodus of people away from Earth, running because they were afraid it was just a matter of time until this particular alien group showed up to bombard us to dust.

[Seret]

It's impossible to guess what kind of technology they might be using. We have no competence at interstellar flight, so we're really not in any position to guess what a civilisation capable of interstellar flight might look like.

What we can make an educated guess about is our reaction. I'm not convinced there'd be much hysteria on Earth, mostly because there wasn't last time. In the late Victorian era it was widely reported that there was an alien civilisation on Mars due to the supposed discovery of their canals. The public took this idea in their stride without going mental.

[Javster]

It's impossible to guess what kind of technology they might be using. We have no competence at interstellar flight, so we're really not in any position to guess what a civilisation capable of interstellar flight might look like.

What we can make an educated guess about is our reaction. I'm not convinced there'd be much hysteria on Earth, mostly because there wasn't last time. In the late Victorian era it was widely reported that there was an alien civilisation on Mars due to the supposed discovery of their canals. The public took this idea in their stride without going mental.

Mainly because we didn't have planes yet. Now we have rockets, the Space Shuttle (according to far too many people) so they could as well. Plus every sci-fi movie will help scare people.

[Rainbowtrout]

Most likely they wouldn't be able to communicate with us. Even if we didn't use speech, they might not even be able to see, smell, taste, etc

[Godot]

Most likely they wouldn't be able to communicate with us. Even if we didn't use speech, they might not even be able to see, smell, taste, etc

Actually that´s nonsense IMHO at least with respect to the visual system ...

I´d expect every highly advanced tool using society to be in possession of a visual system.

Without it I wouldn´t see any way of making the step from ground dwelling to flying ... I´d also see no way how they would get any informations about their own solar system (not to speak of other solar systems) if they don´t possess a visual system.

Edited July 26, 2014 by Godot

[KerikBalm]

Agreed, EM radiation (ie, light) is the only thing that propagates in a vacuum. They will be sensing it, if not organically, then with technology (I suppose they might not have eyes, but they will have something like telescopes and cameras, that is for sure).

So, first question:

Did they know we were here when they left?

They'd likely be able to sense that there was something funny going on based on our oxygen atmosphere, and a prominant green pigment from a long way away - farther than our radio waves would be discernable. If they didn't know we were here when they departed, they'd know before they arrived.

One scenario: Its just a survey ship passing by, maybe looking to do some in situ resource utilization before going on the next leg of its journey - it may stick around for longer observation, or it may just transmit its findings and leave quickly

Another Scenario: They came to study what was producing the oxygen atmosphere - they may or may not make contact, if its obvious we've detected them, they probably would.

Another scenario: They came to colonize the system. Assuming they have fusion drives or better and have adapted to life in space (they may colonize systems with no terrestrial planets) such, they may prefer to start with small gravity wells - it start mining the asteroid belt and Kuiper belt, Earth, with all of its biohazards and its nearly 10 km/s dV requirments, and resources hidden deep underground, may not be attractive to them. However, its industrial output may be of interest to them. If we build stuff for them, they can grow their colony faster. I don't foresee direct enslavement - more like they give us technology, and we have to build stuff for them, perhaps this is arranged via "gunboat diplomacy" - accept, or they bombard us from beyond earth orbit (likely only delivered to governments in secret). Your enslavement is the amount of labor you do that goes towards paying taxes to fund the construction of stuff for the aliens.

Or they just acknowledge our claim to earth, but then claim everything in the system beyond earth orbit for themselves - maybe they'll be nice and let us have the moon too.

I wonder how humanity would react if we saw our potential future (expansion into space) robbed from us?

I don't see a relativistic kill weapon as likely. They are only good against civilizations that are limited to one system with a handful of planets. Civilizations spread across multiple start systems, with self sufficient industry on various asteroids/small moons/etc, could not be readily wiped out by 1 KE weapon. Earth would not pose an existntial threat to them if they're already expanding across start systems. If they're here, they're long past their single inhabited planet stage. A simple warning would suffice, and I think they'd want to study us (a technological space faring civilization wouldn't form if there wasn't some desire for knowledge, don't you think?).

Also, I'm assuming no warp drive. Sorry but I'd still wager that alcubierre drives are impossible, even if they don't strictly violate relativity and haven't been strictly proven to be.

They come, they study, they may or may not colonize the rest of the system, they may or may not seek to use Earth's industrial capacity for their benefit.

We are so small and insiginficant at this point, that we don't pose a threat, and the planet isn't worth much to them - mars would probabl be better suited for their needs anyway

[Rus-Evo]

Another scenario: They came to colonize the system.

So what do we think we own?

Im guessing we all think we own the earth (so no mining of it by aliens).

Im also guessing we think we own the moon.

Do we have first call on Mars? Jupiter? Kuiper Belt? Is the entire solar system ours?

I bet we would not like it if they were mining our solar system!!! But under our own rules for exploration (such as when Europeans were discovering the rest of the world), if you cant go there and dont have a settlement, you don't have such a good claim!

Do we even own earth??

[KASASpace]

What if it's a probe? A self-replicating probe (capable of building more of itself with in-situ utilization. So, a monolith. With knowledge? We can only hope it brings about good things.

Or some kind of "Rama" flying around.......