A better way to phrase the question is: if Mars were inhabited by a civilisation as advanced as ours, what would we need to detect it?
The naked eye?
Backyard telescopes?
Observatories?
Orbital telescopes?
Landers?
The question in reverse: if that civilisation were looking for us, would we be able to conceal our existence? I’m thinking we would need to reduce stray radio waves and maybe hide our satellites, but can they see our cities from Mars?
There are many deserts on earth that would give the impression the planet is uninhabited. A probe could drive around for years and not find life in the Gobi desert.
IANAAA (amateur astronomer) but you’d be able to see lights from large cities on the dark parts of earth with a mid -high range backyard telescope plonked on mars wouldn’t you?
Would you? From images of the Venus transit, the resolution doesn’t seem high enough to make any features out. Not sure if those are the limits of resolution, though.
If it was advanced as ours, we wouldn’t even need telescopes. We would see their satellites in our sky.
Also, even though it may not be intelligent, there’s plenty of life in even the harshest deserts (at least, compared to Mars). You’d need to land by the poles of our planet to have any doubt.
This question was asked in an issue of Sky & Telescope a few years ago. I think the answer was that light from a major city on Earth could be seen from Mars in a large amateur telescope, say a reflector with a 18 inch/.5 meter mirror.
(this is detection by purely visual observation, of course)
Not true at all. The Gobi is teeming with life, both plant and mammal. I don’t think there’s any place on Earth where a probe would fail to find life pretty quickly.
Not necessarily. If they were more advanced than us, those satellites could be invisible for all intents and purposes (we’ve already got fledgling invisibility tech)
The point would stand that if the Martian civilization was as advanced as ours, they’d have the equivalent of a HiRISE camera up in their “Earth Reconnaissance Orbiter” getting extremely high detailed images of the surface of Earth essentially eliminating any doubt as to our existence here.
I don’t know what the highest resolution ground telescope images of Mars are, but Hubble has some images of Mars that are in almost as much detail as say, famous pictures of Earth taken from the Moon so they’d definitely be able to detect civilization with their equivalent of the Hubble.
Just to put a number on it, the resolution of the HiRISE camera is 30 cm, or about one foot. (The Mars Reconnaissance Orbiter’s orbit isn’t particularly low, either.) Many, many, many human structures would be visible at that scale.
