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IsaacKuo
2014-Jul-18, 10:17 PM
If aliens exist in our galaxy, then they might explore the galaxy with inexpensive unmanned probes. Such probes might cruise from star to star, using free gravity assist slingshot flybys to pick up speed and steer from one star to the next. With a velocity of 1000km/s, such probes would take maybe 20 million years to explore the galaxy. That's not much time compared to the over 4 billion years our solar system has been around.

If there are such probes, just passing through, then it's extremely unlikely we would have noticed. Even if one were to pass through today, it would have to be very large for our SOHO or STEREO space telescopes to see. (These regularly see sungrazing comets, but only thanks to the humongous coma.)

But let's suppose a probe is left behind in our solar system rather than just passing through. Would we have seen it yet?

The first question is location. I'm going to assume the probe's location is chosen purely for convenience, with no attempt to hide the probe from us. Where's a good location?


1) On Earth - Bad. A probe on Earth itself would only have a view of a tiny part of Earth, and it would have to somehow survive the elements and unknown dangers from plants/animals/etc.


2) Low Earth Orbit - Bad. A good view, but not stable over the long term.


3) Polar Orbit - Bad. A good view, but not stable over the long term.


4) Equatorial high Earth Orbit - Okay. A good view of most of Earth, but no good view of the poles.

If an alien probe were located here, we would have seen it by now.


5) The Moon - Good. A good view of all of the Earth. There are potential complications in landing on the Moon, as well as long term effects of Moon dust.

If an alien probe were located here, we would almost certainly not have seen it by now. Such a probe might be sitting on the Moon's surface somewhere, staring up at us. Existing high resolution images of the Moon would not be sufficiently detailed to identify such a probe unless it was pretty big (maybe the size of a jetliner).


6) Inclined elliptical solar orbit - Good. A view of all planets, not just Earth, including occasional close encounters for better views of every planet.

If an alien probe were located here, we probably would not have detected it yet. Even if we have detected it, it would seem to be just another very small asteroid or inactive comet without detailed spectral analysis. Even with spectral data, it's entirely possible this probe wouldn't be easy to distinguish from an asteroid/comet.


My conclusion is that if an alien probe in our solar system, located in a good place to observe Earth and/or other planets, it would have been unlikely or impossible for us to have noticed it.

SkepticJ
2014-Jul-18, 10:36 PM
It depends upon your assumptions of what the probe is like.

I can imagine probes that could operate on Earth that we wouldn't notice--notice that they are probes, that is. We would see them, we would just think that they are insects, or whatever. We would have to examine them under a microscope to see the truth, and they would probably avoid giving us the chance to do that. So it would be pretty unlikely that we would discover the truth, unless the density of pseudo-fauna probes was high in the natural population of critters that they're disguised as.

IsaacKuo
2014-Jul-19, 12:53 AM
I am assuming probes basically similar to the space probes we have used, but designed to last many millions of years, or billions of years.

I don't think placing such a probe on Earth itself is such a good idea. I think it would make more sense to design a long lasting probe to operate in the vacuum of space.

Solfe
2014-Jul-19, 01:07 AM
You missed an option. The Earth is the probe. :)

The moon as a probe is a slightly more ominous symbol.

Spacedude
2014-Jul-19, 01:19 PM
How about a probe not on the moon but rather orbiting the moon? Or if we're assuming that ET doesn't want it's probes to be easily discovered perhaps their probes are equipped with alien stealth technology which is beyond our present day detection capabilities.

Paul Beardsley
2014-Jul-19, 01:45 PM
It's one of those things we can't rule out - which is fine just as long as nobody is trying to rule them in either, which I don't think anybody here is.

It's easy enough to envisage a probe a bit like the ones we are capable of building, with a few enhancements such as the ability to recharge from sunlight, regenerate for longevity, and an AI system that makes decisions about whether to go into orbit or slingshot into another solar system. In fact I envisage a fleet (swarm?) of the things which decide between themselves how interesting a solar system looks and from this decide how many should hang around and how many should move on.

I also see no problem with a probe being able to shake off lunar dust.

Now, what about the motivation of the builders? Are they sufficiently long-lived to see the outcome of their project? Even if they have no concept of money, they must be aware that they are squandering resources on a mission that is of limited interest.

But yeah, it makes much more sense than living aliens travelling light years just to fiddle with cows.

IsaacKuo
2014-Jul-19, 01:45 PM
Lunar orbit is not long term stable.

IsaacKuo
2014-Jul-19, 02:15 PM
It's one of those things we can't rule out - which is fine just as long as nobody is trying to rule them in either, which I don't think anybody here is.
It's typical for people to assume they are already ruled out, within our solar system. The usual thing is to assume there is no alien presence in our Solar System. I think this assumption is presumptuous.

My interest is mainly in the other direction. I see the possibility as a promising direction to attempt searching for evidence of alien life (along with SETI, searches for Dyson spheres, spectral analysis of exoplanets, etc. In this case, the sensors involved would be useful for other space missions, such as Sun observation, scientific study of the Moon, and asteroid research. So, it's not necessary to fund such sensors specifically for alien probe searches. Searching for alien probes could piggyback on existing data, much as seaching for Dyson spheres can piggyback on existing research on red dwarfs.

Unfortunately, current sensors and asteroid surveys lack the sensitivity or resolution required to detect a probe on the order of, say, 10m in diameter. But if a probe were, say, 100m in diameter, then searching through lunar data might find it.

Now, what about the motivation of the builders? Are they sufficiently long-lived to see the outcome of their project? Even if they have no concept of money, they must be aware that they are squandering resources on a mission that is of limited interest.
I don't see any inherent reason why aliens would necessarily not have sufficiently long life spans. But I also don't see extremely long life spans as strictly necessary. With a lifespan of only a few thousand years, it would already be feasible to send out interstellar missions at slingshot speeds of 1000km/s (inexpensive if a white dwarf is available). Such missions could start returning data on a different star system within a thousand years. Even at just 100km/s, such missions could start off by returning data on distant planets and Oort cloud objects.

Note that we ourselves have already sent out five probes toward interstellar space, at speeds which are woefully insufficient to return data on other star systems within a human lifetime. When we have advanced technology to allow such probes indefinite self repair capability, such probes might be sent on true interstellar missions. They could start off as flyby missions to study Sedna-like objects, but then continue onward to eventually study other star systems.

Noclevername
2014-Jul-19, 02:36 PM
Self repair technology would imply a power source capable of surviving the journey, which would mean thermal radiation. How would the probe avoid detection of its waste heat?

IsaacKuo
2014-Jul-19, 02:45 PM
As a baseline, I assume the most practical long term power source is solar power. The photon flux going out would be the same as that going in, like an asteroid or inactive comet. Even if there were an extra heat source, though, this would merely increase the estimate of the size of such a small object.

Paul Beardsley
2014-Jul-19, 02:52 PM
It's typical for people to assume they are already ruled out, within our solar system. The usual thing is to assume there is no alien presence in our Solar System. I think this assumption is presumptuous.

I don't think it's presumptuous; it is simply practical. By all means speculate about what might be there, and how we would find a probe if there were a probe to find. But until we find evidence that there actually is a probe, it seems wisest not to assume that there is.


Note that we ourselves have already sent out five probes toward interstellar space, at speeds which are woefully insufficient to return data on other star systems within a human lifetime. When we have advanced technology to allow such probes indefinite self repair capability, such probes might be sent on true interstellar missions. They could start off as flyby missions to study Sedna-like objects, but then continue onward to eventually study other star systems.

I have no problem with the idea of other civilisations doing this.

Noclevername
2014-Jul-19, 02:58 PM
As a baseline, I assume the most practical long term power source is solar power. The photon flux going out would be the same as that going in, like an asteroid or inactive comet. Even if there were an extra heat source, though, this would merely increase the estimate of the size of such a small object.

But some of that solar energy would be used as work, so it would (IIRC) result in a higher than normal temperature. When the probe gets in from deep space it will have been without energy and repairs for a long time, have cosmic ray and dust damage, and have a lot of fixing up and setting up to do, so it would make more heat than an inert object. And once it gets into the Solar system it will have ongoing damage from solar wind, solar flares, and a higher concentration of micro-debris.

IsaacKuo
2014-Jul-19, 03:18 PM
I don't think it's presumptuous; it is simply practical. By all means speculate about what might be there, and how we would find a probe if there were a probe to find. But until we find evidence that there actually is a probe, it seems wisest not to assume that there is.
As I said, the usual assumption is that an alien probe within the solar system is already ruled out by the evidence. It is presumptuous to assume this.

The truth is that it has not been ruled out, and we really only have evidence that there is no probe in Earth orbit (which is not an ideal location because long term stable Earth orbits lack a view of the poles).

Paul Beardsley
2014-Jul-19, 03:33 PM
As I said, the usual assumption is that an alien probe within the solar system is already ruled out by the evidence. It is presumptuous to assume this.

The truth is that it has not been ruled out, and we really only have evidence that there is no probe in Earth orbit (which is not an ideal location because long term stable Earth orbits lack a view of the poles).

Whose usual assumption? Please give names because otherwise this is beginning to sound like one of those strawman arguments that make these potentially interesting discussions so tedious. I am not aware of anybody having said, "It's safe to say there are no alien probes in our solar system."

Unlike aliens visiting Earth in their flying saucers (which I believe can be ruled out), I consider alien probes firmly in the "maybe, maybe not" category

IsaacKuo
2014-Jul-19, 03:50 PM
Whose usual assumption?
Most people who mention the Fermi Paradox. I'm not talking about just this forum, I'm more active on Google+.

Usually, when the Fermi Paradox is brought up, the presumption is that there is no alien presence within the solar system.

I think it's because the Fermi Paradox is not mysterious to people who realize there could be alien spacecraft nearby that we haven't seen yet. It's only mysterious to people who think we must have seen evidence of alien spacecraft if they were around. Thus, those people would tend to be the ones who bring it up for discussion.

Please give names because otherwise this is beginning to sound like one of those strawman arguments that make these potentially interesting discussions so tedious. I am not aware of anybody having said, "It's safe to say there are no alien probes in our solar system."
This is one reason I don't bother posting on Cosmoquest often. I can't even mention possible ways to look for evidence of alien life without getting into a stupid argument over whether or not we should even admit the possibility of finding it.

IsaacKuo
2014-Jul-19, 03:53 PM
But some of that solar energy would be used as work, so it would (IIRC) result in a higher than normal temperature. When the probe gets in from deep space it will have been without energy and repairs for a long time, have cosmic ray and dust damage, and have a lot of fixing up and setting up to do, so it would make more heat than an inert object. And once it gets into the Solar system it will have ongoing damage from solar wind, solar flares, and a higher concentration of micro-debris.
No, the overall outgoing photon flux would actually be slightly lower, because some of that energy went toward useful work. Not by a detectable degree, I'd expect.

The temperature could be slightly lower, due to enthalpy, but only to a similar degree as sunlight being absorbed by a dark material.

profloater
2014-Jul-19, 04:09 PM
Just for fun, if we designed such a probe, it would be superblack so it would look like a rock and it would orient itself with beam type transmitter to send back only in the direction of home. It would probably be aimed (with slingshots etc) at a target star known to have suitable planets and designed to go into solar orbit well away from the planets for stability. And it assumes a very long life designer/society, we would not get funding for a thousand year project! Except maybe in the last million years of our star life.

Hlafordlaes
2014-Jul-19, 09:54 PM
I like the OP idea. I've usually ended up in this kind of thread arguing for probes of some kind being likely for advanced civilizations, and for time not necessarily being an issue, such as for a machine civilization or one with high longevity. I also think that if the probes had good instrumentation and were consistently relaying info back progressively, the initiating civilization could simply travel via artificial reality among the rich data, mindful only of its atemporal nature.

Granted, we have to retain a proper skeptical stance, but the only reason not to look locally, instead of only at other systems, would be cost, if that were an issue. Otherwise, cataloging the solar system in detail with an open mind seems fine and dandy to me.

Colin Robinson
2014-Jul-20, 05:00 AM
Most people who mention the Fermi Paradox. I'm not talking about just this forum, I'm more active on Google+.

Usually, when the Fermi Paradox is brought up, the presumption is that there is no alien presence within the solar system.

I think it's because the Fermi Paradox is not mysterious to people who realize there could be alien spacecraft nearby that we haven't seen yet. It's only mysterious to people who think we must have seen evidence of alien spacecraft if they were around. Thus, those people would tend to be the ones who bring it up for discussion.

Interesting point...

I've heard that the long list of seriously-discussed resolutions of the Fermi paradox includes the proposition that "they are here unobserved". (Whatever "here" means.) I think you've put forward quite a plausible scenario of how that might be the case (if "here" means "within this solar system"): Interstellar travel exists, its motive is scientific observation, the most efficient method of observation is a long-lived probe placed in solar orbit.

marsbug
2014-Jul-20, 03:27 PM
A small probe that transmits back to home only in occasional bursts - or transmits via a more powerful but distant relay station (say at the solar focus) - might be very hard to spot. It would get all but impossible to spot if we allow that our hypothetical alien civ might have an arbitrarily high level of technology, and so might have a very different idea what 'close by' means - for example a probe with much more powerful sensors than we can currently conceive could be located in the Kuiper belt, or even further out, and we'd never see it.

As for interacting with us.. in the internet age a probe might be online with us without our knowing. Some small, ultra paranoid, part of my brain has been half expecting a post from someone who has just joined the forum to show up that just reads
Re the OP: Yes, yes I am. :) :) :) :D :D

Colin Robinson
2014-Jul-20, 10:31 PM
A small probe that transmits back to home only in occasional bursts - or transmits via a more powerful but distant relay station (say at the solar focus) - might be very hard to spot. It would get all but impossible to spot if we allow that our hypothetical alien civ might have an arbitrarily high level of technology, and so might have a very different idea what 'close by' means - for example a probe with much more powerful sensors than we can currently conceive could be located in the Kuiper belt, or even further out, and we'd never see it.

As for interacting with us.. in the internet age a probe might be online with us without our knowing. Some small, ultra paranoid, part of my brain has been half expecting a post from someone who has just joined the forum to show up that just reads :) :) :) :D :D

In case ETs do have access to the internet, there is actually a website set up some years back by a team of SETI people which invites them to have a constructive dialog via email. The team have a procedure for distinguishing between messages from genuine ETs and human hoaxers. So far they haven't received any messages they consider to be genuine.

Invitation to ETI (http://ieti.org/index.html)

IsaacKuo
2014-Jul-21, 08:04 PM
A small probe that transmits back to home only in occasional bursts - or transmits via a more powerful but distant relay station (say at the solar focus) - might be very hard to spot.
I assume the probe would use some sort of beamed communications in any case. The energy efficiency without a tight beam is astronomically awful. It makes sense for any communications to be tightly focused toward the home system or relay station, and thus not directly visible to us.

Direct communications with a home system halfway across the galaxy might require a large transmitter; the size of such a probe may make it more readily visible to us.

But your suggestion of a relay station at solar focus may be more practical. The probe wouldn't need such a large transmitter, and the power requirements could be quite low:

http://www.centauri-dreams.org/?p=10123

The relay station may not have any practical power source other than the probe's communication beam itself. But the power requirements may be minimal. It could mainly be a large passive reflector or diffraction array to reflect the beam almost 180 degrees (from the probe toward the Sun).

Note that I'm assuming the mission is designed with no effort toward hiding the probe from us. The design decision to use a gravity lens relay station would plausibly be to greatly reduce the required spacecraft mass and power.

Jens
2014-Jul-22, 03:49 AM
As I said, the usual assumption is that an alien probe within the solar system is already ruled out by the evidence. It is presumptuous to assume this.


I don't know if this is the usual assumption. It certainly isn't my assumption. Like Paul, I would definitely not assume that there is one, and see no reason to believe there are any, but I would certainly not assume that they are "ruled out."

Jens
2014-Jul-22, 03:53 AM
Usually, when the Fermi Paradox is brought up, the presumption is that there is no alien presence within the solar system.

Is that really true? I would say the presumption is that there appears to be no alien presence within the solar system. I think the whole Fermi paradox is based on a question of appearance, not fact, i.e. that we don't see aliens even though there should be lots around. So one of the possible solutions of the paradox could be "because they're invisible" or something like that.



This is one reason I don't bother posting on Cosmoquest often. I can't even mention possible ways to look for evidence of alien life without getting into a stupid argument over whether or not we should even admit the possibility of finding it.

I don't think it's a stupid argument. You are the one who said that others assume that the possibility is "ruled out," but I don't think it is a usual assumption. Do you really think it is?

Senior Service
2014-Jul-22, 10:32 AM
Absence of evidence isn't evidence of absence, or presence in this case. I'm with Paul and Jens on the likelihood or otherwise of a probe.

To go back to the OP: I suspect any probe wouldn't be on Earth unless they already knew there was life here, it would surely be better to have it in orbit/patrol in the solar System to check out multiple planets and to have passed through numerous other systems on the way here.

Edit to expand for clarity.

IsaacKuo
2014-Jul-22, 12:47 PM
Is that really true? I would say the presumption is that there appears to be no alien presence within the solar system.
This wording implies exactly what I said--that the evidence suggests there is no alien presence within the solar system.

This goes beyond merely that we don't know whether or not there is an alien presence within the solar system due to lack of supporting evidence either way (except for most of Earth and Earth orbit).

It suggests that we should have seen such an alien presence if it exists.

I think the whole Fermi paradox is based on a question of appearance, not fact, i.e. that we don't see aliens even though there should be lots around.
This argument is common--there is the presumption that if aliens exist, at least one of them must have colonized the galaxy in a way that populates every star system in an extremely visible way. This presumption assumes that we humans are a good example of expanding to every possible location on Earth so it would be impossible to fail to notice humans on Earth, and that we will expand into the galaxy in a way that does the same thing to all other star systems.

Whether or not this line of thinking is valid, it is a very common line of thinking. It is used to argue that there are no aliens in our solar system (because if there were, we should have seen them by now).

That goes beyond just a question of appearance.

If it is just a question of appearance, then so what? Who cares? I can say that I can't see any white cats from here. But this is not a very interesting observation for me to make. It says nothing about whether or not any white cats exist within even a 100m radius. It says something about whether or not a white cat exists in this room, but it would be presumptuous to think it says anything about whether or not white cats exist in this city.

I don't think it's a stupid argument. You are the one who said that others assume that the possibility is "ruled out," but I don't think it is a usual assumption. Do you really think it is?
I think it's a stupid argument, and we're having it right now. And what is the point of this argument? What is there to be gained by it?

We're basically arguing over the meaning of "there appears to be no alien presence within the solar system".

I think it would be more interesting to consider the technical possibilities of how an interstellar probe mission would be designed, and how we would look for one. That's why I find the question of interstellar communication interesting to consider. It would be an interesting technical challenge for us to do, and it might provide a way to figure out what to look for in a hypothetical alien probe within our solar system.

IsaacKuo
2014-Jul-22, 01:03 PM
Just for fun, if we designed such a probe, it would be superblack so it would look like a rock and it would orient itself with beam type transmitter to send back only in the direction of home. It would probably be aimed (with slingshots etc) at a target star known to have suitable planets and designed to go into solar orbit well away from the planets for stability. And it assumes a very long life designer/society, we would not get funding for a thousand year project! Except maybe in the last million years of our star life.
I think such a probe may plausibly be very black due to development of efficient solar panels and efficient telescopic sensors, rather than a specific attempt at stealth.

As for funding for the mission...assuming we humans don't greatly extend our lifespans (a big assumption, perhaps), the mission could still be funded if it were primarily designed for something else. In particular, KBOs, Oort cloud objects, and the solar focal point are all good primary mission objectives for a probe on a solar escape trajectory.

Hoof Hearted
2014-Jul-22, 03:00 PM
Sometimes it's hard to spot a probe which is in the same room.

Jens
2014-Jul-23, 03:58 AM
This goes beyond merely that we don't know whether or not there is an alien presence within the solar system due to lack of supporting evidence either way (except for most of Earth and Earth orbit).
It suggests that we should have seen such an alien presence if it exists.

I don't know if it does. I could say the same thing about whether there's a man with a knife behind me. I have no evidence one way or the other, since I'm facing my computer, so in fact it doesn't go beyond merely that I don't know. And it does not suggest that I should have seen such a knife-wielding person if he existed, because he could be hiding behind something, so it's not implied. But on the other hand, it doesn't mean the person is as likely to exist as not to exist. My assumption would naturally be that there isn't such a person behind me unless I have some reason to believe there is. [/QUOTE]



Whether or not this line of thinking is valid, it is a very common line of thinking. It is used to argue that there are no aliens in our solar system (because if there were, we should have seen them by now).

I'm not sure who puts forth that line of thinking, but it seems pretty absurd to me. As we are discussing in this thread, there could be probes that we're not aware of. The solar system is a very big place.



I think it's a stupid argument, and we're having it right now. And what is the point of this argument? What is there to be gained by it?

Well, we're both responding to one another, so we must be getting something out of it, I'd guess.



I think it would be more interesting to consider the technical possibilities of how an interstellar probe mission would be designed, and how we would look for one. That's why I find the question of interstellar communication interesting to consider. It would be an interesting technical challenge for us to do, and it might provide a way to figure out what to look for in a hypothetical alien probe within our solar system.

I don't know if I'd say "more interesting," but I do agree it's an interesting speculation, to consider how we might detect hypothetical alien probes in our solar system.

kzb
2014-Jul-23, 12:35 PM
These probes have to send a signal out of some sort, which in principle makes them detectable.

The logical thing to do would be to have a mothership probe in solar orbit further out than Earth. This is big enough to generate the power to send signals back home periodically, but without being detectable from Earth.

It's possible for the mothership probe to send out sprites for closer range observations every now and then. These are probes the size of a chip, and they can keep themselves in Earth orbit for as long as required by adjusting their aspect to solar radiation. They send out weak signals with only enough range to reach the mothership probe. Once finished with they are allowed to deorbit and burn up.

BTW, the scenario is intentionally stealth-like I would say. Otherwise why not just land your probe on Earth and say Hi?

IsaacKuo
2014-Jul-23, 02:22 PM
I don't know if it does. I could say the same thing about whether there's a man with a knife behind me. I have no evidence one way or the other, since I'm facing my computer, so in fact it doesn't go beyond merely that I don't know.
No, saying the same thing in that case would be, "It appears there is no man with a knife behind me." That goes beyond saying that you don't know.

IsaacKuo
2014-Jul-23, 02:46 PM
These probes have to send a signal out of some sort, which in principle makes them detectable.
Only with great difficulty and purposeful effort. Such a signal would not be detectable from Earth, because:

1) Such a signal would have to be tightly directional in order to have a useful range.

and

2) It makes no sense to send such a communications signal toward Earth, since Earth is a large predictable obstacle.

In order to try and look for such a signal, we'd need to rely upon space probes which might luckily be in between the probe and its target.


The logical thing to do would be to have a mothership probe in solar orbit further out than Earth. This is big enough to generate the power to send signals back home periodically, but without being detectable from Earth.

It's possible for the mothership probe to send out sprites for closer range observations every now and then. These are probes the size of a chip, and they can keep themselves in Earth orbit for as long as required by adjusting their aspect to solar radiation. They send out weak signals with only enough range to reach the mothership probe. Once finished with they are allowed to deorbit and burn up.

BTW, the scenario is intentionally stealth-like I would say. Otherwise why not just land your probe on Earth and say Hi?
I am considering scenarios which are not intentially stealth-like in any way. In the scenarios I'm considering, the alien probe mission is designed purely in terms of long term practicality.

A gravity lens communications relay may be good because the power requirements are extremely low. (This is described above). The probe could use a tiny amount of power and a reasonably sized dish or phased array transmitter (maybe 3m or less), if there's a relay mirror at the solar focus.

However, I also like the idea of a relay that's much further away. The Sun is rather noisy in a lot of wavelengths, but a white dwarf would be much dimmer and far easier to shade out. Isolated white dwarfs would be ideal locations for gravity lens relays. Using the Sun for a long term gravity lens relay is also complicated by alignment issues--good alignment is required for a double-ended gravity lens (gravity lenses on both ends)...but the Sun itself moves around significantly due to Jupiter and other planets.

kzb
2014-Jul-24, 12:06 PM
If it's not intentionally stealth-like, you have to make up a plausible reason as to why it is accidentally stealth-like.

If you are indifferent to whether your probe is detected or not, the logical thing is to have the probe close by Earth and most likely in orbit around it. Possibly also sending down landers like Cassini, and in contact with some kind of advanced relay system like you describe. In this way you maximise your information return, but the probe is detectable.

So you see the problem, why would you choose to NOT maximise your information return if you weren't bothered about being detected? You need a reason for this.

Colin Robinson
2014-Jul-24, 12:12 PM
BTW, the scenario is intentionally stealth-like I would say. Otherwise why not just land your probe on Earth and say Hi?

Seems to me that there are three scenarios to consider:
1.ETs want humans to know about them.
2.ETs want humans to remain unaware of them.
3.ETs don't care whether humans become aware of them or not.

1. Landing on Earth and saying "hi", or beaming a radio signal towards Earth, are things ETs could do if they wanted humans to know about them.
2. Stealth technology is what they could do if they wanted humans to remain unaware of them.
3. If they don't care either way, then it would be logical for them to do what Isaac has suggested observe Earth and the rest of this solar system by means of a long-lived probe in solar orbit, with no attempt either to disguise it or to draw attention to it.

Hlafordlaes
2014-Jul-24, 12:42 PM
One thing I think very highly likely is that if a probe were sent this way and is here now, when launched ET would have had no sign of anything advanced in these parts, so no attempt at stealth. Stealth would only come into play if, unlike Sagan's optimism, their probes were all sent out under the assumption that contact in general can be very dangerous.

I'm such a paranoid at times that if I were to announce to the world today that I've invented some incredibly good tech for exploring the galaxy in short measure, I'd also announce that the launch hub would be located in another solar system, or that there would be some subterfuge undertaken such that the location of Earth is not communicated in any way.

I mean, everyone knows ETs suck brains, no?

IsaacKuo
2014-Jul-24, 01:32 PM
If it's not intentionally stealth-like, you have to make up a plausible reason as to why it is accidentally stealth-like.
As Colin notes, I'm thinking in terms of ETs that don't care whether humans are aware of the probes or not.

If you are indifferent to whether your probe is detected or not, the logical thing is to have the probe close by Earth and most likely in orbit around it.
As I note in the first post, a polar orbit is not long term stable, and an equatorial orbit does not have a good view of the poles. The best Earth "orbit" location would actually be on the surface of the Moon, on the near side somewhere. (Other potentially good orbits are ruled out by gravitational interaction with the Moon itself.)

A probe on the surface of the Moon could be detected by future high resolution surveys of the Moon, or maybe even by an existing high resolution survey if it's big enough (on the order of the size of an airliner).

Possibly also sending down landers like Cassini, and in contact with some kind of advanced relay system like you describe. In this way you maximise your information return, but the probe is detectable.
An Earth lander plausibly won't last for thousands of years, much less millions or billions. The information return would be extremely brief and limited compared to a probe operating in the vacuum of space. And as I also noted in the first post, a probe located on Earth itself would have an extremely limited view.

So you see the problem, why would you choose to NOT maximise your information return if you weren't bothered about being detected? You need a reason for this.
I described reasons for preferring a probe located either in an inclined solar orbit or on the surface of the Moon. In my opinion, of course.

Much depends on the assumptions going in, naturally. I'm thinking in terms of a probe that uses cheap propulsion to only cruise around at 1000km/s or less (1000km/s is a reasonable long distance cruise speed from white dwarf to white dwarf, but you'd only want to approach the Sun at 100km/s or less in order to do a cheap orbital insertion burn.) Depending on how far away the probe is coming from, it may have traveled millions of years before reaching the Sun. This isn't a mission with Earth humans specifically in mind...we didn't even exist that long ago.

OTOH, Hlafordlaes does have a point that maybe probes are plausibly designed under the assumption that contact in general can be dangerous. Perhaps so. I'm operating the assumption that the probes are designed the way our probes are designed--with no stealth in mind at all, nor with any designed capabilities to attempt contact (except with the operators). This is mainly a simplifying assumption to make the thought experiment more manageable. But also, the thought experiment is meant to lead to ideas for actually looking for such a probe. It seems pretty hopeless for us to try and find look for a stealthy probe, seeing as it would already so difficult for us to see one that's just sitting out there in the open.

Conversely, I'm also thinking in terms of us designing a mission to send out such an interstellar probe ourselves. This is enough of a challenge without adding on stealth requirements and/or alien contact capabilities.

KABOOM
2014-Jul-24, 04:13 PM
Agree that the most likely alien exploration of our galaxy would have been launched without any specific knowledge of "life on Earth" (although perhaps our Solar System may have been a candidate). As Issac suggests our solar system could simply be just one stop on a very long journey.

Given the above, I would think that such an explorartory mission would have some type of on-board AI that would identify Earth as an area of "extreme interest" once a routine inventory of our solar system had been made. Therefore, the "to be stealth" or "not stealth" variable inevitably arises and a decision as to how to proceed would then result.

Leads me to conclude that, IF, our system is being "explored", THEN it must be in a designed stealth manner.

Jens
2014-Jul-24, 10:59 PM
.
Leads me to conclude that, IF, our system is being "explored", THEN it must be in a designed stealth manner.

In general, when we send out probes out we don't seem particularly eager to either to broadcast or conceal our existence, so I don't know if we need to assume that others would act any differently.

kzb
2014-Jul-25, 11:55 AM
In general, when we send out probes out we don't seem particularly eager to either to broadcast or conceal our existence, so I don't know if we need to assume that others would act any differently.

The Voyagers have the plaques and the LP records.
Although I think that if it was suspected the target planet could host an intelligent species, that would generate a lot of controversy about whether it should be stealthy mission or a greeting mission.

I think the stealth argument would win out actually. People will argue for a Prime Directive for less advanced species, and to proceed with extreme stealth if it is thought the species was technologically advanced.

Either option calls for intentional stealth, and if we think like that, there's no reason ET wouldn't think that as well.

kzb
2014-Jul-25, 12:08 PM
IsaacKuo: a probe capable of interstellar travel and inserting itself at preferred locations in a stellar system will almost certainly be capable of making minor adjustments to an orbit around Earth. Even without that, it is possible to have a high enough orbit that it will last almost forever, and that is much nearer than the Moon.

Conversely, I'm also thinking in terms of us designing a mission to send out such an interstellar probe ourselves. This is enough of a challenge without adding on stealth requirements and/or alien contact capabilities

Well it does raise an interesting point. I wonder if there are any such protocols being established for interstellar probes? Let's hope they are before you launch yours !

IsaacKuo
2014-Jul-25, 04:25 PM
IsaacKuo: a probe capable of interstellar travel and inserting itself at preferred locations in a stellar system will almost certainly be capable of making minor adjustments to an orbit around Earth.
The delta-v requirements to maintain an unstable orbit will be very high over thousands or millions of years. The delta-v requirements for the probe to travel via gravity assist (as I suggest) are low.

Even without that, it is possible to have a high enough orbit that it will last almost forever, and that is much nearer than the Moon.
That's fine for equatorial orbits, but an orbit inclined enough to have a good view of the poles will suffer from the Kozai mechanism--sending the probe into Earth.

The Voyagers have the plaques and the LP records.
All five of our interstellar probes have some sort of incidental message-in-a-bottle, but these do absolutely nothing to increase or decrease an alien's ability to detect the probes.

We have made explicit attempts at broadcasting communications attempts (METI signals), but these are not related to our space probes.

Although I think that if it was suspected the target planet could host an intelligent species, that would generate a lot of controversy about whether it should be stealthy mission or a greeting mission.
You are correct that our attitudes may change if we seriously expect a space probe could encounter an intelligent species. But I wouldn't be sure about what effect it would have either way.

On the one hand, we might plausibly be paranoid and make the probes stealthy. On the other hand, we might not seriously care about what might happen in thousands or millions of years after a KBO probe completes its primary mission and eventually settles in some interesting star system.

Note that there may be an inherent bias for less paranoid people to be the ones who send out such a probe in the first place...

Luckmeister
2014-Jul-25, 05:34 PM
Either option calls for intentional stealth, and if we think like that, there's no reason ET wouldn't think that as well.

Really? So you assume ET thinks like us?


....and we don't all think like that. There is disagreement on whether we should be stealthy or advertise our existence.

Paul Beardsley
2014-Jul-25, 07:45 PM
That's fine for equatorial orbits, but an orbit inclined enough to have a good view of the poles will suffer from the Kozai mechanism--sending the probe into Earth.

You keep mentioning the poles thing as if it were a show-stopper. It seems to me a matter of options - for the same budget, you've got a choice of:

1. Long-term view of the whole planet but from quite a long way away.
2. Close-up view of the whole planet but for not very long.
3. Close up long-term view of the planet but with a limited view of the polar region.

Unless you have an unlimited budget that enables you to send out multiple probes, you just have to decide where your main interests lie.

IsaacKuo
2014-Jul-25, 08:23 PM
You keep mentioning the poles thing as if it were a show-stopper. It seems to me a matter of options - for the same budget, you've got a choice of:

1. Long-term view of the whole planet but from quite a long way away.
2. Close-up view of the whole planet but for not very long.
3. Close up long-term view of the planet but with a limited view of the polar region.

Unless you have an unlimited budget that enables you to send out multiple probes, you just have to decide where your main interests lie.
I explicitly list these three choices in my first post (options 3, 4, 5). I give my rating of them, rating them "Good", "Bad", and "Okay". These ratings are a question of priorities and opinion, sure.

My thinking is that data from a long term probe over millions of years would be more interesting than a detailed one time snapshot (only a hundred or a thousand years being a one time snapshot, over the timescales of gravity slingshot travel across the galaxy).

I have another reason for concentrating on long term probes--a short term probe would likely not be visible to us because it already complete its mission billions of years ago. If it were set in a short term polar orbit, with only enough fuel to last a few centuries, then it would have completed its mission and then burnt up in Earth's atmosphere ages ago. My interest is in a probe which we may have a chance to detect.

Note that I posit the use of an elliptical solar orbit which repeatedly comes somewhat close to all planets. It might only get closer than an Earth-Moon distance occasionally, but it will continue to do so indefinitely.

eburacum45
2014-Jul-26, 09:34 AM
An interesting idea; what would the mission statement of such a probe be? Would it observe Earth (and all the other planets) continually, or at periodic intervals? What would it do with the data? I'd like to think that such a probe could be smart enough and adaptable enough to process its own observations, and adapt its own behaviour to the data it perceives. This would be quite a challenge over billions of years. There would be other issues too - billions of years in a dusty vacuum filled with solar photons and cosmic rays would cause degradation, which would need to be repaired.

Would such a probe report back to its makers? If so, how would it know where they are? After a few million years, proper motion would basically randomise the orbit of the home star around the galaxy, so either the probe would lose contact, or some sort of homing signal would need to be transmitted from the home star to maintain contact. These would be powerful transmissions aimed at the Solar System, and probably detectable - but they would be very rare events. In due course these homing signals might cease, for various reasons, leaving the probe with nowhere to report to.

I like the idea of a superannuated probe in elliptical solar orbit, or camoflaged on or beneath the surface of the Moon or other object; could it be lonely? Could it be insane, thanks to cosmic ray degradation or sheer ennui? Could we make friends with it?

publiusr
2014-Jul-26, 05:39 PM
In "The sentinel" Clarke mentioned an object atop a mountain on the moon. That would place it above most of the lunar dust--with the craggy rock perhaps being cleaned. That would last a good while. Plenty of sunlight.

Triana's orbit might be good
http://en.wikipedia.org/wiki/Deep_Space_Climate_Observatory

IsaacKuo
2014-Jul-26, 08:10 PM
An interesting idea; what would the mission statement of such a probe be? Would it observe Earth (and all the other planets) continually, or at periodic intervals?
The more I think about it, the more I like the idea of a solar elliptical orbit...but with little inclination. Earlier, I suggested an inclined orbit. I was thinking in terms of having nice views of the poles of all planets, but from a distance.

A low inclination orbit wouldn't have good views of the poles most of the time. But a low inclination orbit would have much closer flyby encounters with planets, and during these close flyby encounters, polar observation is possible (typically, only one pole will be observable per flyby, but it's random which one). Unfortunately, a close flyby can knock an orbit out-of-plane, and a close flyby of a gas giant can knock the orbit into solar escape. The probe would have to carefully avoid such situations.

What would it do with the data? I'd like to think that such a probe could be smart enough and adaptable enough to process its own observations, and adapt its own behaviour to the data it perceives. This would be quite a challenge over billions of years. There would be other issues too - billions of years in a dusty vacuum filled with solar photons and cosmic rays would cause degradation, which would need to be repaired.
I assume some capability of self repair. As for what it does with the data? Well, observations of the star(s) and major planets/moons would be used to navigate. Not much delta-v is required if the probe can predict its future trajectory accurately. Other than that, I'm assuming it mainly just takes observations and determines the most interesting data to transmit back home. The intelligence involved in making this determination might not be very high though--maybe only on par with Kepler. Or maybe it's very sophisticated.

Would such a probe report back to its makers? If so, how would it know where they are? After a few million years, proper motion would basically randomise the orbit of the home star around the galaxy, so either the probe would lose contact, or some sort of homing signal would need to be transmitted from the home star to maintain contact. These would be powerful transmissions aimed at the Solar System, and probably detectable - but they would be very rare events. In due course these homing signals might cease, for various reasons, leaving the probe with nowhere to report to.
I speculate that the "home" it transmits back to might not be the ultimate destination of the data, but rather the nearest communications relay system. I suspect isolated white dwarf systems may be the ideal locations for such relay systems, due to the lack of orbit-driven wobbles and the dimness of a white dwarf star (making it very good for gravity lenses).

Even as dim as a white dwarf is, though, it's still going to shine with quite a lot of light. A probe could plausibly be able to keep track of it without the assistance of a homing beam.

Hlafordlaes
2014-Jul-26, 08:18 PM
So, IK, are you writing this up in a story? Maybe you could tease with some plot points.

IsaacKuo
2014-Jul-26, 09:16 PM
So, IK, are you writing this up in a story? Maybe you could tease with some plot points.
No story. I'm mainly pondering this topic to consider possible ways to try and search for an alien probe or rule out the existence of one or more plausible locations.

Previously, I was considering how to search for pure flyby probes (probes which don't dwell in any one star system, but rather endlessly cruise from star to star via gravity slingshots). My hope was that SOHO or STEREO might provide a way to look for one if we were lucky enough to have one pass through. But it turned out that they simply aren't sensitive enough to see a probe unless it were huge.

I don't think this search would warrant dedicated use of telescope time, much less a dedicated space telescope mission. But it could plausibly be a search which could piggyback on sensor data gathered for other things, such as an asteroid survey.

Hlafordlaes
2014-Jul-26, 11:13 PM
I don't think this search would warrant dedicated use of telescope time, much less a dedicated space telescope mission. But it could plausibly be a search which could piggyback on sensor data gathered for other things, such as an asteroid survey.

In the end, we do need to end up examining the entire system in detail for all kinds of reasons. Be nice if we found a probe. What a game changer.

heidihock
2014-Aug-06, 11:27 AM
For me Alien is probably with US since then. But weather they exist or not as long as they are not hurting us for me It's okay.

Dave12308
2014-Aug-20, 04:50 PM
This is one reason I don't bother posting on Cosmoquest often. I can't even mention possible ways to look for evidence of alien life without getting into a stupid argument over whether or not we should even admit the possibility of finding it.

This is one of the most difficult forums to post in that I belong to; and in fact is the only forum on the internet that I have seen where I almost feel "too stupid" to post in here.

It's like everything has to be absolutely PURE SCIENCE and being a non-scientist I cannot even fathom how to word my thoughts in a way as to not gain myself an infraction.

I have a lot of theories and ideas but the way this place is I am afraid to post them. So I am mostly a lurker who reads.

Dave12308
2014-Aug-20, 04:53 PM
In case ETs do have access to the internet, there is actually a website set up some years back by a team of SETI people which invites them to have a constructive dialog via email. The team have a procedure for distinguishing between messages from genuine ETs and human hoaxers. So far they haven't received any messages they consider to be genuine.

Invitation to ETI (http://ieti.org/index.html)

Wow, not only do we assume they are capable of understanding human speech patterns............ We are also arrogant enough to assume they speak English!

IsaacKuo
2014-Aug-20, 08:32 PM
This is one of the most difficult forums to post in that I belong to; and in fact is the only forum on the internet that I have seen where I almost feel "too stupid" to post in here.

It's like everything has to be absolutely PURE SCIENCE and being a non-scientist I cannot even fathom how to word my thoughts in a way as to not gain myself an infraction.

I have a lot of theories and ideas but the way this place is I am afraid to post them. So I am mostly a lurker who reads.

For many subjects, posting ideas on this forum is a good way to vet them and learn more about the subjects. The old USENET forum rec.arts.sf.science served that role for me. I posted a lot of dumb ideas on rec.arts.sf.science, but this led me to learn a lot (this was before Yahoo, Google, and Wikipedia). I thought I had learned a lot from reading things in libraries, but there's nothing like putting something past some people who know more to weed out your own misconceptions!

But there are some subjects which have become toxic here. Alien life is one of them, global warming is another. SLS may be another (if you don't know what SLS is, don't worry about it).

Paul Beardsley
2014-Aug-20, 09:12 PM
Wow, not only do we assume they are capable of understanding human speech patterns............ We are also arrogant enough to assume they speak English!

Probably best to avoid using the word "arrogant" in connection with aliens unless you know what the words mean.

Jens
2014-Aug-21, 01:56 AM
Wow, not only do we assume they are capable of understanding human speech patterns............ We are also arrogant enough to assume they speak English!

That's a perfect example of why people hesitate to post, I'm afraid. They risk being accused of arrogance by other posters.

Jens
2014-Aug-21, 02:32 AM
But there are some subjects which have become toxic here. Alien life is one of them, global warming is another. SLS may be another (if you don't know what SLS is, don't worry about it).

For global warming I think you are correct, but akin life seems to be a subject that comes up frequently, and I personally find the views expressed interesting and enlightening. It is very much to the point on this board. The "toxicity" perhaps is due to the fact that there are certain members that seem to have very strong opinions, one way or the other, on this question.

Colin Robinson
2014-Aug-21, 04:14 AM
Wow, not only do we assume they are capable of understanding human speech patterns............ We are also arrogant enough to assume they speak English!

I think the word "conjecture" is more exact in this context than "assume". The online "Invitation to ETI" is an experiment based on the conjecture that some form of extra-terrestrial intelligence may have access to the internet, and may be able to understand a message in English, which is a major language of the internet.

casey10s
2014-Aug-25, 05:57 PM
One thing to consider is why our period of time is any more important than any other time period. If you don’t think it is, then why would one expect an alien contact event to occur within our recorded history? Recorded history is at best about 10,000 years old which is a small time period if you look at the age of modern humans (1 million years?), larger multi-cellular organisms (500 million years), and existence of Earth (4.5 billion years). Something could have flown through the solar system, circled the earth, landed on Earth, took samples, etc. and no one would have known it. A probe could have landed on Earth or any planet in the solar system, say 500,000 years ago and probably all traces of it are gone or so absorbed into the planet that it would be an extremely lucky chance to find any traces.

My ideas would be that a civilization could send out many relatively cheap probes throughout a section of space. The probes would basically gather data, maybe make some basic analysis, and send this data back to the home base. These probes would either pass through a solar system or orbit at some great distance from the start that might make them almost undetectable but would provide them with an easy method to gather data. Based on the data received, more elaborate and expensive probes could be sent to the areas that may have some interest. Or, these cheap probes would be sent again at a later time to do another check to see if anything new or interesting has developed since the last time.

Whether Earth would be classified as a point of interest can be debated. I don’t think humans would be considered equals to an alien race with this type of technology. If the aliens are anything like humans, I feel that aliens would treat humans the same way as humans treat chimpanzees, dolphins, and other more intelligent animals. This goes back to why is our time period any more special than any other time period. Humans may be interesting studies but an alien might not want to have debate teams with humans due to their inferiority. Maybe another 1000 years in the future, this could change.

Also, I have problems with a probe beaming a highly directional signal back to its home planet or relay station. Wouldn’t some signal coming from the other direction be expected? I would think either an acknowledge signal, new commands, updates from the home base, etc, would be sent to these probes This should be able to be detected unless the signal looks so much like background noise for whatever reason. Of course, these signals could be transmitted but not within our 100 years of being able to detect such signals.

As for detecting their communication or technology, maybe there are other technologies that haven’t been invented by humans but are highly used by advanced technologies. If you go back to the early 1800’s, could anyone have detected an over the air television signal, a wireless communication, or some other more recent communication medium? We could be at the same disadvantage. We just haven’t come across these new technologies (yet).

Maybe as we find new technologies, we can detect these probes if they exist. As for now, maybe the probes are so difficult to detect due to the huge area that they can be in or the technology is not available to detect them in a reasonable amount of time and effort due to the technology used in the design of the probes.

IsaacKuo
2014-Aug-26, 03:52 PM
One thing to consider is why our period of time is any more important than any other time period. If you don’t think it is, then why would one expect an alien contact event to occur within our recorded history? Recorded history is at best about 10,000 years old which is a small time period if you look at the age of modern humans (1 million years?), larger multi-cellular organisms (500 million years), and existence of Earth (4.5 billion years). Something could have flown through the solar system, circled the earth, landed on Earth, took samples, etc. and no one would have known it. A probe could have landed on Earth or any planet in the solar system, say 500,000 years ago and probably all traces of it are gone or so absorbed into the planet that it would be an extremely lucky chance to find any traces.
I agree with these speculations, which is why I suggest the idea of long term probes. It may be hopeless to look for a flyby probe or a short term probe, for the reasons you state.

Also, I have problems with a probe beaming a highly directional signal back to its home planet or relay station. Wouldn’t some signal coming from the other direction be expected? I would think either an acknowledge signal, new commands, updates from the home base, etc, would be sent to these probes This should be able to be detected unless the signal looks so much like background noise for whatever reason. Of course, these signals could be transmitted but not within our 100 years of being able to detect such signals.
For purposes of this discussion, I am assuming that the probe is a scientific probe with a mission of gathering data. As such, it's unclear that communications in the other direction are even necessary. I imagine command data being sent infrequently, if at all, in order to redirect a probe to another target or to change its mission priorities.

There's also a matter of technical capabilities. A gravitational lens works best in one direction. A probe can send a signal to a far away gravitational lens without worrying too much about alignment--the receiver can track the probe's orbital movement on its end simply by moving the receiver a bit. But it doesn't work in the other direction, because orbital motion can't be predicted years in advance with sufficient precision.

As for detecting their communication or technology, maybe there are other technologies that haven’t been invented by humans but are highly used by advanced technologies.
This is true, but we can't really guess the properties of such technology.

A baseline assumption of a probe using photon beam communications gives us an idea of how big and powerful a probe would have to be--if using such technology. Presumably, an advanced alternative would only be used if it were superior to this, so the baseline assumption at least gives us a cap on the size of a probe.

neilzero
2014-Aug-26, 06:35 PM
We are extravagant with our waste heat, but I think we know how to recover most of it down to liquid helium temperatures where it would not be detected by present infrared telescopes.