VLBI SETI: Detecting Signals in Gliese 581 System

[Chronos]

This paper marks a targeted attempt to detect SETI signals in the Gliese 581 system.
The First Very Long Baseline Interferometric SETI Experiment
http://arxiv.org/abs/1205.6466
Apparently more such targeted surverys are planned using candidates identified by Kepler. Given the high resolution and sensitivity of the VLBI, this looks very interesting.

 

[surajt88]

Turns out, they observed the region for 8 hours in a range of radio frequencies and they heard nothing. :(

zeenews.india.com/news/space/new-targeted-et-hunt-fails-to-find-alien-signals_779302.html

 

[shifty88]

Interesting article.
Would it ever be possible to detect extra-terrestrial civilisations by listening out for RFI transmissions

couldn't the radio wave be trashed by passing through a gas cloud or affected by the gravitational pull of a star, planet or black hole.
Also wouldn't the frequency of the wave be stretched out by the expansion of the space its passing through and as a result never reach us or reach us in a distorted incomprehensible manner and make it indistinguishable from naturally occurring radio waves in the cosmos

Finally, would we be able to pinpoint the origin of the radio wave if the above comes into effect

 

[marcus]

Interesting article.
Would it ever be possible to detect extra-terrestrial civilisations by listening out for RFI transmissions

couldn't the radio wave be trashed by passing through a gas cloud or affected by the gravitational pull of a star, planet or black hole.
Also wouldn't the frequency of the wave be stretched out by the expansion of the space its passing through and as a result never reach us or reach us in a distorted incomprehensible manner and make it indistinguishable from naturally occurring radio waves in the cosmos

Finally, would we be able to pinpoint the origin of the radio wave if the above comes into effect

SETI searches typically involve stars in our own Milkyway galaxy---stars that are a few tens or hundreds of lightyears away. The galaxy radius is only a few tens of thousands of LY.

There is no noticeable redshift or "stretching" of signals over such short distances. Redshift occurs over distances like 100 million LY or larger.

About "pinpointing", the VLBI is highly directional. Large antennas spaced widely apart.

About "affected by the gravity" of a star, black hole, etc. I don't imagine there is much chance of that kind of interference when VLBI is used to listen for radio signal from a nearby star. There is not very much in the way, and we would already have noticed the effect of some unexpected gravitational lensing in optical telescope images of these stars.
Stars only a few tens or hundreds of LY away are very well known and have been photographed many times. I don't think there's a problem with unexpected distortion of the putative signal.

The problem, I would guess, is the RARITY of identified hab zone planets. Out of on the order of a thousand identified planets, only a handful are classed as habitable. I don't recall how many so far: two or three?

And you might have to look at (wild guess) hundreds of habitable planets before there's a reasonable chance of detecting signal. Surely if you just look at three habitable candidates you couldn't reasonably expect to find a signal. There might be nobody but seaweed and fungus living there

 

[shifty88]

i was thinking out loud. thanks for clearing it up. I should of probably known all that as well.

I guess patience is in order. depends how long a planet has been noisy for or so i hear

How long would it take for a radio transmission to travel a hundred light years.
We just have to get lucky i guess
personally I can't wait for the day we discover extra terrestrial life

 

[Irishwake]

i was thinking out loud. thanks for clearing it up. I should of probably known all that as well.

I guess patience is in order. depends how long a planet has been noisy for or so i hear

How long would it take for a radio transmission to travel a hundred light years.
We just have to get lucky i guess
personally I can't wait for the day we discover extra terrestrial life

We've probably got a better chance of every quick-pick lottery ticket for a given drawing randomly selecting the same set of 5 numbers than we do finding "nearby" life transmitting in radio waves. As an example, look at humans. We've hardly had the ability to communicate with radio waves for 120 years, and we're already well on our way to more sophisticated means of communication. Now you have to factor the narrow window that radio broadcasts are even generated into your equation. If we find ET in a nearby star system, it's not going to be because we picked up their radio broadcast.

For what it's worth though, I hope I'm wrong.

 

[mfb]

The problem, I would guess, is the RARITY of identified hab zone planets. Out of on the order of a thousand identified planets, only a handful are classed as habitable. I don't recall how many so far: two or three?

Don't forget the bias from to the detection method - hot jupiters are much more likely to be detected than earth-like planets.

How long would it take for a radio transmission to travel a hundred light years.

100 years, as space is a good approximation for a vacuum.

Even with the most optimistic assumptions, the probability to have extraterrestrial life with a similar technology level (radio transmissions, but no sufficiently advanced technology) at nearby stars is really small.
Personally, I think that spectroscopy of planetary atmospheres is a better approach. On earth, the composition of the atmosphere depends crucially on life for at least ~2 billion years.