Regarding the high presence of iron on the surface: is this not a side-effect of the impact that made the Moon? The theory being that the lighter material became the Moon, and the heavier stuff stayed on Earth.
A. SETI agrees with you. While I know the folks at SETI would “take” leakage if they could, really what they hope to find is an intentional signal broadcast at narrow-band frequencies (which are the most efficient in terms of producing a detectable signal at the receiving end) and where SETI looks. Also, if ET are using high-powered radars for (actual SETI Institute example) finding incoming comets, they will generate the type of signals SETI can find. Other than that, SETI is very open that we won’t find them using our current radio equipment – esp. the kind of leakage inadvertent stuff you talk about.
B. SETI agrees with you.
Alien civilizations are thought by many to be at least as likely to use visible light signals for communicating as they are to use radio transmissions. Visible light can form tight beams, be incredibly intense, and its high frequencies allow it to carry enormous amounts of information. Using only Earth 2006 technology, a bright, tightly-focused light beam, such as a laser, can be ten thousand times as bright as its parent star for a brief instant. Such a beam could be easily observed from enormous distances.
The Planetary Society and Harvard just opened a new Telescope to search for visible light from ET.
All these arguments about how life can can only come about with liquid water, with the planet only so far from the sun and not too far, or the star system has to be just so far out from the center of the galaxy, I think these are all logical fallacies.
We only have one point of data about life. Assuming all life in the universe has to have our requirements is simply silly.
Once we fire up the warp drive and start finding other life, then we can start making fairly accurate predictions about where life can and cannot arise. We can barely imagine how life arose here, let alone how it came about in other radically different environments.
Sure, there are theories about how life might rise from silicon or whatever, but face it, water and carbon make it relatively easy. Look at the amazing variety of life here on earth. Life is everywhere, on and under the surface, in oceans and skies. So we know that it’s very likely that this combination could produce life in a number of different planetary environments.
Until we find an ammonia based life form however, our best bet is to start with what we know. Besides, whatever substances they might arise from, we have yet to hear from them, or at least recognize that we are hearing from them.
As Snag suggests, there are very good reasons, based in chemistry, to believe that life as we know it is somewhat more likely than the alternatives. Here’s a GD thread from a couple of years ago about the water question, for example.
I assume you mean “if the Earth’s orbit were 1% smaller or 1% larger”. IIRC the margin is not quite that small but around 5%. And yes, really. Temperature has to be between ~273K and ~373 K, which obtain in only miniscule portions of the universe but modest areas of the sun’s orbit. Both Venus and Mars miss out on the habitable zone by quite small margins, whereas the earth is smack in the middle of it at the moment (it moves outwards as the sun grows hotter). Venus could well have been in it in the early history of the solar system, but other conditions would still have made it uninhabitable in all likelihood.
Pfft, that ain’t gonna ever happen. 
Another challenge to SETI, besides the use of bands of EM radiation which remain unsearched, is the problem of compression. Any civilization advanced enough to generate a signal we’d be likely to hear also probably makes use of data compression to maximize bandwidth. The better the level of compression, the more like random noise a signal appears to one without the proper decompression algorithm.
Thanks, I was trying to say “orbital diameter.” It’s an eerie thought, anyway… 5% seems like nothing.
Actually, it is possible that liquid water might exist outside of the comfort zone if for instance a moon, such as Europa which does seem to be covered in ice, is close enough to a body with a very strong gravitational pull such as Jupiter’s. Tidal forces could possibly keep some of the ice in a liquid state beneath the ice on top despite the extreme cold.
It may also be possible that a planet with a very hot core could also use geothermal heat to liquify water on a frozen world before it cools too much, but this may not be very likely. The world would need a very thin crust as I understand it.
But given some time and the right amino acids in place, it may be possible for life to start while water is in a liquid state and then adapts to cooler temperatures later. But for it to become technically capable intelligent life? It boggles my mind to consider it unless it has a very long time to evolve should it’s world be outside of a temperate orbit.
But on an earth-sized moon circling a mega-gas giant a few times the size of Jupiter or Saturn? Perhaps.
But, any broadcast intentionally directed outward, to other stars, would presumably not be compressed — unless the aliens are practical jokers who enjoy being difficult.
It’s those deliberate out-bound signals that SETI is trying to find, I believe. The hope of detecting the leakage from locally broadcast signals is almost nil.
Bummer. So odds are we won’t detect TV footage of Proxima Centauri’s version of Big Brother, then.
No, but the Centaurans’ car dealership commercials will come through loud and clear.
Those don’t count as intelligent communication though.
We’ll probably pick up their cell phone calls, too, which might not count either.
And not always easy to get funding for, and not always taken as seriously as it might be by astronomers working in other sub-fields.
"Liquid water on Saturn moon could support life"
:eek:
That’s it. I’m moving there. After that, the next time you hear from me, my name will be “She.”