Could An ExtraTerrestrial Find Earth with a Telescope?

Active Seti writes "If aliens were hunting life outside their own planet, could they peer through the vastness of space and lock onto Earth as a likely home for life? Researchers say with a roughly Hubble-sized array observers could measure Earth's 24-hour rotation period, possibly leading to observations of oceans and the chance of life. 'They would only be able to see Earth as a single pixel, rather than resolving it to take a picture,' said Astronomer Eric Ford. 'But that could be enough for them to identify our planet as one that likely contains clouds and oceans of liquid water.' The research will be useful to astronomers designing the next generation of space telescopes on our planet, because it provides an outline of the capabilities required for studying the surfaces of Earth-like worlds."

oxygen, man

[Quadraginta]

Phoo, once you've detected O2 in the atmosphere, you're done. Only life could produce that much free oxidizer in a strongly reducing universe.

Re:Too many assumptions?

[Liquidrage]

There's a lot to that discussion. We tend to assume that the laws of physics will work pretty much all over the galaxy. And in places where our current understandings break down, life isn't likely to exist (black holes, Planck scales, etc...).

Given this assumption, there aren't a lot of options for different types of life. The chemistry just doesn't work. Biology is chemistry, chemistry is physics, and physics is mathematics. It basically puts in some ground rules for life. There's a decent little wiki on this: http://en.wikipedia.org/wiki/Alternative_biochemistry [wikipedia.org]

As you can see in that wiki (there are pro's and con's for each of the alternates), based on our understanding life either does need most of the same things we do, or at least our biochemistry should be the most common in the universe. The math just makes it that way. There are some variables sure. And some alternatives. But for the most part, looking for stuff life us seems to most likely scenario.

Now, given this, #1 and #2 should fall somewhat in line with what they're thinking. Sure, the minutia of evolution could lead to exotic live from our perspective. Something other then DNA based life even. But they (the aliens) should still come up with e=mc And their biochemistry should, at least, be something comparable to ours.

Re:I've got an idea

[esper]

It's only been about 100 years since Marconi invented the radiotelegraph. Even if we assume that they would be 100% certain to pick up any signal we've sent, no matter how weak, and that they would be 100% able to recognize it as carrying meaning, any civilization more than 100 light years or so away would still have no inkling of our existence based on unnatural radio transmissions. A 100 light year sphere is a pretty small chunk of space compared to the rest of our galaxy. Much too small of a chunk to draw strong conclusions from, IMO.

Re:pixelization

[imsabbel]

I see your humor, but...

A single pixel can provide a hell of a lot of information: Do spectroscopy, and you can get the typical absorption lines (O2 for example should be easy to detect, and be a sure way for _anybody_ who detects it to tell something is odd about that planet).
Track the intensity over time, and you can get the rotation period.

Re:A pentagon-shaped smiley?

[Rhinobird]

What the hell. Most of the Wiccans I've met are perfectly ok people. Wierd, but nice.