Earth-like exoplanet discovered around Proxima Centauri

JeanTate said:
If there were radio telescopes on Proxima b just like those here on Earth, when would unusual radio signals from our solar system have first been detected (assume the relevant radio telescopes were pointed in our direction at the time; also assume Proxima b has an ionosphere which blocks radio the same way ours does)?
Click to expand...

What signal do you think would be detectable? As you noted, a lot of signals never leave Earth due to the ionosphere. Most broadcast signals aren't focused enough to remain detectable even inside our solar system even if they aren't blocked by the ionosphere. Some radar beams are focused (and narrow enough bandwidth) enough to remain detectable at a nearby planet, but, since they are a focused beam, they aren't likely to actually hit a planet.

Voyager isn't all that far yet, but even at it's relatively nearby distance, communicating with it requires both it and us knowing exactly where each other is, exactly what frequency is being used, and what the signal means to remain in communication.
 
Last edited:
RecoveringYuppy said:
What signal do you think would be detectable? As you noted, a lot of signals never leave Earth due to the ionosphere. Most broadcast signals aren't focused enough to remain detectable even inside our solar system even if they aren't blocked by the ionosphere. Some radar beams are focused (and narrow enough bandwidth) enough to remain detectable at a nearby planet, but, since they are a focused beam, they aren't likely to actually hit a planet.

Voyager isn't all that far yet, but even at it's relatively nearby distance, communicating with it requires both it and us knowing exactly where each other is, exactly what frequency is being used, and what the signal means to remain in communication.
Click to expand...
OK, let's do some calculations ...

Current radio astronomy facilities can easily detect signals of 1 milliJy, and it's been many a year (over a decade) that ~microJy signals have been detected. Current plans including possibly reaching ~nanoJy levels.

Assume the Earth's radio emission is isotropic (it isn't, as you point out, but let's be as conservative as possible).

What is the total power (in W) of all man-made radio emissions, that get through the ionosphere, averaged over a day or so, today?
 
I come up with Earth's entire electrical generating capacity being 5TW (5x10^12). I come up with the surface of a 4 light year radius sphere being 1.7x10^34 square meters. Spread Earth's entire generating capacity across that surface and I get 2.7x10^-22. If I then spread that across only 10K Hz I'm at the jansky level. Spread it across 10MHz (only two TV channels wide) and I'm milli-jansky levels already.

http://mecometer.com/topic/electricity-installed-generating-capacity/

4LY in meters = 4x365x86400x300000x1000
 
JeanTate said:
(my hilite)

This is, surely, one of the most interesting questions re exolife! :)

We won't know until we actually find such, right?

In fact, we won't really know anything about exolife until we find some, right?

All the plausibility reasoning is nice, and may help re where to look for such life, and how, but it can take us only so far, right?
Click to expand...
Yes indeed. But suppose we discover from, let us say, a very advanced analysis of the atmosphere of a planet, that there is some organism there engaged in the cultivation of plants. We would perhaps assume that this implies the presence of intelligence, but that would not be necessarily so, as the example of termites indicates.
 
JeanTate said:
... Current radio astronomy facilities can easily detect signals of 1 milliJy, and it's been many a year (over a decade) that ~microJy signals have been detected. Current plans including possibly reaching ~nanoJy levels.
Click to expand...

I'm not sure what you mean here(?)

Although its meaningful to characterize the sensitivity of radio telescopes in Janskys, the Jansky is not the appropriate unit of measure for the sensitivity of a SETI receiver. Sensitivity for SETI reception is simply in Watts per square meter(?)
(Ie: SETI RF searches seek narrowband signals with distinguishable signal to noise ratios).
 
Last edited:
Speaking of radio astronomy...

An Interesting SETI Candidate in Hercules

A candidate signal for SETI is a welcome sign that our efforts in that direction may one day pay off. An international team of researchers has announced the detection of “a strong signal in the direction of HD164595” in a document now being circulated through contact person Alexander Panov. The detection was made with the RATAN-600 radio telescope in Zelenchukskaya, in the Karachay–Cherkess Republic of Russia, not far from the border with Georgia in the Caucasus.

The signal was received on May 15, 2015, 18:01:15.65 (sidereal time), at a wavelength of 2.7 cm. The estimated amplitude of the signal is 750 mJy.
Click to expand...
 
SelfSim said:
I'm not sure what you mean here(?)

Although its meaningful to characterize the sensitivity of radio telescopes in Janskys, the Jansky is not the appropriate unit of measure for the sensitivity of a SETI receiver. Sensitivity for SETI reception is simply in Watts per square meter(?)
(Ie: SETI RF searches seek narrowband signals with distinguishable signal to noise ratios).
Click to expand...

Can you provide a cite for what you are talking about? The jansky is the right unit for what she was talking about. It would be the right unit for most receivers. You can reduce it to watts per square meter if you assume a given bandwidth but that is hardly a fundamental distinction.
 
Last edited:
RecoveringYuppy said:
Can you provide a cite for what you are talking about? The jansky is the right unit for what she was talking about. It would be the right unit for most receivers. You can reduce it to watts per square meter if you assume a given bandwidth but that is hardly a fundamental distinction.
Click to expand...

Digital signal processing is usually the means for achieving the required sensitivity and it effectively reduces the instantaneous channel bandwidth. This filters out a lot of background noise, which works if the signal being looked for is also very narrow. This technique also effectively renders the Jansky unit as pretty well meaningless for directed SETI searches, so Watts per square meter makes more sense, if the application we're talking about is directing all Earth's RF emissions into a single directed signal(?)

I may have misunderstood what Jean meant however(??) .. Which is why I asked for clarification. Its no big deal - just looking for clarity.
 
Do you have a link for what your are talking about?

If you'll just read back a few posts you'll find we were talking about picking up Earth's radio emissions at a great distance.
 
The same applies to any antenna.

A Yagi will have a much greater signal strength at a given distance per watt transmitted at a given frequency than will a dipole. A dish will have even greater signal strength. Furthermore, that can be increased by using a directional antenna at the receiving end; point to point transmission using a dish-to-dish system results in high signal strenth with micro-watts of power due to the gain of the antennae.
 
RecoveringYuppy said:
What are you replying to?
Click to expand...

I was just commenting in general about reception over great distances.

IMO, non-directional transmissions such a TV and Radio broadcasts, even one that can exit the ionosphere, are far less likely to be received in the vicinity of a nearby star than a transmission directed at the star in question.

It is highly unlikely that any intelligent species with reception capability would be able to receive any of the broadcast we have been making since Marconi's time, but a directed, high power (in the order of megawatts) transmission using a large radio telescope such as the CSIRO dish at Parkes in NSW, would stand a much greater chance of being received.
 
smartcooky said:
... It is highly unlikely that any intelligent species with reception capability would be able to receive any of the broadcast we have been making since Marconi's time, but a directed, high power (in the order of megawatts) transmission using a large radio telescope such as the CSIRO dish at Parkes in NSW, would stand a much greater chance of being received.
Click to expand...

Does the Parkes observatory have transmission capability?
 
To help get a feel for detectability of our own interstellar messages, I've put together the following analysis. (Its based on one of Jill Tarter's papers here).

So, the Arecibo message was sent in 1974, so what is the detectability of this signal?

- According to Tarter, she starts out being generous by improving our receiving technology by two orders of magnitude beyond our present stage of technological development .. She indicates the best we can do with this magic improvement is to barely detect a signal of flux density of 1x10-28 W/m2. (This calls for using an arrayed antenna complex like the SKA);

- Using the above improved SKA type array, the Arecibo message signal is only barely detectable at a distance of only about 15,000 lyrs, when transmitted by technologies used in the powerful (Arecibo) radar system. M13 was the original target. It is about 25,000 lyrs distant .. ie: well beyond the above improved technology's detectability range - (which provides one answer for the question posed above). There are about 6x109 stars within the 15,000 lyrs range, but these are not on the line of sight chosen for the Arecibo message.

- So, extrapolating even further into the more distant future, she then improves, by yet another order of magnitude the sensitivity to detect a flux density of 1x10-29 W/m2. How much further out could we see in this instance? The answer she gives is about 50,000 lyrs. (She estimates there are about 6x1010 stars within this range).

Thus, according to her, we'd need about 3 orders of magnitude improvement in signal (flux density) detection technology, in order to detect our own Arecibo message .. (that's if we were the ETIs sitting inside the M13 cluster). I suppose it could also be said that 'this might be doable', over the intervening period of 25,000 years which it will take for the Arecibo message to actually get to M13.
 
smartcooky said:
I think he is equating intelligence with industrial civilization.

Its possible to have intelligence with no industrialized civilization, but not the other way around.

The presence in an exoplanet's atmosphere of certain chemicals such as chlorofluorocarbons containing reactive halogens from man-made halocarbons would be a clear indication of the presence of an industrialized civilization
Click to expand...

That, but any form of life capable of occupying large parts of a planet's surface or oceans will change the atmosphere in ways dead rock would not.
 
You must log in or register to reply here.

Back
Top Bottom