I’ve been reading a lot of Carl Sagan books as of late and his discussion in Pale Blue Dot about how hard it would be to recognize civilization on Earth from a distance got me wondering about an opposite scenario.
Say an alien race landed a probe, one similar to the Viking landers we put on Mars, on Earth. More likely than not it would land in some remote location, an ocean, jungle, tundra, or something of that nature. If this scenario were to actually take place, what are the chances we would know about it? Would we be able to detect something that small as it approached Earth? And if we could would we be able to recognize it as something other than debris?
As vague as your question is, I wouldn’t be surprised to see it moved to another forum, to give it space for people to speculate. It’s not real close to a question with a factual answer. Just sayin’
If we assume that the aliens made any effort at all to avoid detection, we wouldn’t see it. It would probably show up on photographs from satellites, but there’s no good automated way to scan all of the data for alien probes. If a human happened to look at that particular spot of the globe in Google Earth, e might notice it, but the Earth is large enough that the odds are very low of any person actually looking at that particulat spot.
At most, it would be noticed as a particularly bright meteor, and folks do sometimes try to hunt down the impact point of bright meteors. But they’re often not successful.
You do realize that the images on Google Earth are not real-time satellite images. They are compiled from aerial photos that are months or even years old.
Something the size of a Viking probe, and coming in at interstellar (or at least interplanetary) velocities would be almost immediately picked up Ballistic Missile Early Warning System and PAVE PAWS radars and Defense Support Program satellites if it was on any track that flies over North America or the North Pole. The Russians presumably still maintain their own early warning systems over the Eurasian landmass. Landings in the Southern Hemisphere and particularly Antarctica could be unseen, especially if they were a direct (non fractional orbit) landing.
One would assume, though, that an alien species capable of interstellar transportation could be stealthy enough (if they chose to do so) not to be detected, or to make the probe appear to be nothing more than a random meteor to be catalogued and, as time and interest allow, to be found.
You’d have to assume that, unlike our own probes, the alien probe wouldn’t be designed to beam back information to the home planet. A signal coming from the depths of the jungle would be noticeable.
If it were like the Viking landers then it would be paired with an orbiter. Even if we missed the lander, we’d probably notice the orbiter and any communications going on between them.
Seems to me an alien probe would probably be fairly intelligent though, and would start picking up radio signals from earth by the time it got to within 30-40 lights years of us (which means it’s probably not even here yet) and would slow down and approach cautiously.
True, I hadn’t considered that. Though an alien race intent on secrecy could probably beam the transmission tightly enough to still escape notice.
And I do know that Google maps are old, but that just means that people won’t notice it five years from now, instead of not noticing today. I can’t see that that makes much difference.
Would this probe be programmed to shoot deadly laser blasts at any Rebel scum who happens upon it? 'Cause if so, you might need several witnesses, to better ensure one survives the encounter to report it.
It would be noticeable to anyone with a radio but why would it be noticed? Unless it interfed with a business’ signal no one would give the broadcast any notice.
Sure they would. They’d assume it was a distress signal or some wreckage from an airplane or a spy signal. Nobody can broadcast a signal from anywhere on earth continually (or in regular bursts) without someone noticing and monitoring. (Especially a remote location.) If it doesn’t correspond with any known entity, it will be investigated. Guaranteed.
Every frequency is allocated to someone, and the broadcasts will step on somebody’s frequency.
Take a look at the U.S. Frequency Allocation Chart. One of the most amazing charts you will ever see. You can buy it as a poster for $13, IIRC. Well worth it.
This assumes that the aliens will be broadcasting using a radio frequency transmitter. It seems much more likely, if their intent is to be stealthy, that they’d use a very narrow band transmitter in a microwave or optical range, something with a tight enough beam and sufficient precision to transmit without much leakage or reflection. Better yet, they could transmit information by accelerating neutral pions to close to c, timing the contraction so that they decay at just right at the receiver, and it would be virtually impossible to detect them, even if you knew there was a signal. (You’d have to figure out some workable modulation scheme, but our Slimy Green Aliens have either spent decades transiting through interstellar space or have some indistinguishable-from-magic superluminal propulsion system, so I think this paltry problem is a trivial exercise for them.)
Actually, they’d pick the signals up about 100 lightyears from Earth. IIRC, some time in the 20th Century, we became the brightest radio object in our solar system. (Which makes me wonder if some of the objects radio telescopes pick up aren’t simply the degraded TV transmissions of some alien world that we can’t recognize as such since they’re in a different format and/or have degraded so badly.)
As a WAG, I’d say that any alien probes have to be about 30 or so years out, as we’re still around. (I just know that when aliens pick up things like the Osmond Show and BJ and the Bear, they’re going to wipe us all out.)
I disagree. My satellite modem is transmitting to a satellite 22,240 miles away; I don’t have the manual at hand, but I believe it’s less than a Watt. The arc to “see” a communications satellite is two degrees. The question would be not seeing the signal, but whatever device was receiving it. How high an orbit and what size do we Terrans track with those astronaut gloves and cameras?
Well, if they know we’re here (and it’d be kind of hard for them not to notice), then they’d have to make a decision. Either they want us to know about them, or they don’t. If they wanted us to know, they’d make it abundantly clear, and wouldn’t rely on a single artificial meteor hitting the planet (or a few vivisected cows, or some tramped-down wheat) to say “hi”. So that leaves the possibility that they don’t want us to know.
Wouldn’t work. The lifespan of particles like pions is just an average, not an absolute. So if some are decaying right at the alien relay satellite, some will also be decaying at lower heights. The net effect is that you’d see a glowing beam of light pointing up from the probe, like depictions of lasers in bad science fiction. You’d be better off using a laser beam, and just turning it off when atmospheric scattering was high.
The Ballistic Missile Early Warning System was the kind of thing that I was thinking about when I posted the question, but I hadn’t even thought of the fact that the probe would most likely be sending out signals (via radio or some other communication method). This has turned into a more interesting discussion than I had anticipated.
