First SETI Search of Gliese 581 Finds No Signs of ET

by Nancy Atkinson on June 5, 2012

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An artist’s impression of Gliese 581d, an exoplanet about 20.3 light-years away from Earth, in the constellation Libra. Credit: NASA

The first targeted SETI search of a system with a potentially habitable world has come up empty, but perhaps finding signals wasn’t the main objective in this search. Back in 2007 a group of astronomers used the Australian Long Baseline Array to listen for radio signals from Gliese 581, a red dwarf star that is now known to host at least six planets, with one in the star’s habitable zone. This was a SETI-type search for extraterrestrial-made signals, and it initially found 222 candidate signals. However, the team was able to reject all of them using automated analysis techniques, determining they were caused by Earth orbiting satellites. So why is this potentially good news?

This search was actually a proof of concept for using the Very Long Baseline Interferometry (VLBI) for targeted SETI searches, and that it worked well is great news for future searches that look specifically at a particular star system. Until recently most SETI searches were wide sky surveys, scanning wide, random areas of space looking for radio signals. But now, with the success of the exoplanet hunting Kepler mission, we now know of some potentially habitable systems and planets, and astronomers can do targeted searches, looking at specific spots in the sky.

It wasn’t known if the VLBI technique would be successful for such a “directed” targeted search, but this search by Hayden Rampadarath and team from the International Centre for Radio Astronomy Research at Curtin University in Australia proves it does.

The Australian Long Baseline Array is a combination of three radio antennae: the 22-meter Mopra Telescope, Parkes Observatory and the Australia Telescope Compact Array (ATCA) which are each a few hundred kilometers apart from each other. The data from the three locations are combined, making them act as one huge radio telescope, with an extraordinary angular resolution in the milli-arcsecond regime, the highest resolution in astronomy. And it turns out that VLBI techniques are great for SETI searches because they automatically exclude many Earth-based sources of interference that might otherwise look like SETI signals. That’s because the same signals have to show up at all the telescopes several hundred kilometers apart.

The team pointed the telescopes at Gliese 581 (Gl581), located 20 light-years distant in the constellation Libra for about 8 hours, tuning into frequencies close to 1500 megahertz.

The team said that the array would have been able to pick up a broadcast with a power output of at least 7 megaWatts per hertz, which means that if Gliese inhabitants had been broadcasting directly to Earth using an 300-meter Arecibo-style dish, the signals would have easily been picked up. However, ordinary radio transmissions, such as the ones Earthlings regularly transmit into space, would have been too weak to be detected.

But this bodes well for using other more powerful VLBI arrays such as the European VLBI Network, current most-sensitive VLBI array in the world or the upcoming Square Kilometre Array, which will have the sensitivity to pick up broadcasts of a few kilowatts per Hertz from 20 light years away.

So while this doesn’t mean that there is no life in the Gliese 581 system, this does mean we now have an expanded arsenal of tools for looking.

Read the team’s paper.

Source: Technology Review Blog

About 

Nancy Atkinson is Universe Today's Senior Editor. She also is the host of the NASA Lunar Science Institute podcast and works with Astronomy Cast. Nancy is also a NASA/JPL Solar System Ambassador.

gekkehenkie June 5, 2012 at 5:47 PM

We do not even know if there is a planet with life there, So it is not a surprise. We will never find a other intelligent life form because we are the only one in this galaxie.

Seti is a wast of time

Maybe 1 in the 10000 spiral galaxies have 1 intelligent life. We will never meet them and they will never meet us. We just need to except that we are alone in our part of the universe.

There is good news we will never fight a war with a other intelligent species and this galaxie will belong to the human race

ikma June 5, 2012 at 6:39 PM

you don’t think that statement is a bit too… definitive?

Severin June 5, 2012 at 8:19 PM

First of all, we will neven know if we don’t look. The fact is that we can’t rule out other civilizations out there, just like we can’t rule out that we are alone.

Lets say that there is intelligent life out there,and we one day detect a signal. Unfortunately for us the travel distance is simply to grand to overcome. Does that mean that the purpuse of searching is gone? No. Why? let me explain this one to you.

KNOWLEDGE. Think about the knowlede we could achieve simply by communicating via our transmitters. It might take eight years to get a response from a potential planet in our closest neighborhood solarsystem, and it might take fourty years for a response from Gliese 581. So if there is anyone out there within the reach for communication, wouldn’t you want to know what they have to say?

That is, of course, if there is any. You see what I’m doing? I’m keeping it real, but I’m not denying the possibility. Why? BECAUSE SIMPLY DON’T KNOW YET.

Imagine if the researchers behind these projects shared the same state of mind as you “oh well…there’s probably nothing out there..let’s not bother…zzz” and the day after a signal strock by earth and nobody was listening.

So when you say “A waste of time”, I suggest to you get your pesimistic and unquestionably uneducated bum back to school and start reading about the possibilities in the universe that are yet to be explored.

The point is nobody here knows, and we won’t know if we don’t look.
That does’t mean that there’s no point in exploring and searching extraterrestrial life. Your bomastic statements sounds like religious propaganda.

lcrowell June 6, 2012 at 2:05 AM

The analysis I did of solar system stability lead to the prospect that only between 100 to 1000 planets in our galaxy may have conditions similar to Earth. This might mean that only that many planets in this galaxy have complex life and ecosystem or biomes. There may be many more planets with microbial ecosystems living on the “margins.” Mars or Europa might be such a place. However only a complex biome-planet could give rise to intelligent life.

The probabilities that any of these in our galaxy has intelligent life is pretty small. Out of the 500 million year history of this planet there is only a 100,000 year period with Homo sapiens and two centuries where we had scientifically based technology. It could mean that the nearest galaxy with intelligent life that is on our past light cone or on the Hubble frame is 50 million light years away.

LC

Uncle_Fred June 8, 2012 at 9:02 PM

I’m curious LC, what were the parameters that you used to derive that 100-1000 planet figure? In your calculation, what constitutes as Earth-like? Considering an analysis of Kepler results, wouldn’t terrestrial planets be so numerous as to significantly increase the odds of an Earth-Analog?

I thought we were looking at around 50-150 light year radius for such a planet.

lcrowell June 9, 2012 at 1:55 AM

This stems from my analysis of the stability of the solar system I did last decade. I ran long term numerical calculations of the three body problem of the Sun, Jupiter and Earth. I found that over a 10,000 year time period there was a drift of the Earth outwards. The orbit of the Earth on a short term basis vibrates about its orbit due to Jovian gravity. The periodicity is not exact, and so there is a chaotic drift that sets in. An analysis of these frequencies leads to a 1/f term that corresponds to this outward drift. This is why I think Earth was around .85AU at its inception and has drifted outwards since. This has kept the temperature on Earth relativity constant as the Sun has heated up over time. This should persist into the future as well, thus preventing a boiling up of the Earth environment in 500 million years and postponing that for a billion years or so.

I then extended this some. The 1/f drift corresponds to a Lyapunov exponent due to this perturbation. I then ran through the list of extrasolar planetary systems that had been found at the time. I estimated what would be the Lyapunov exponent for a planet around G-class stars at 1AU given the orbits of the known gas giants. I found only one extrasolar system which was somewhat close to the small value for the Earth. Most were much larger, which means a terrestrial planet at 1AU would be heavily perturbed and would not likely exist in a stable orbit. I then did a Bayesian analysis to estimate how many stellar systems might support a planet at 1AU with an outwards drift comparable to Earth. Initially I found that maybe a few hundred would exist in the whole galaxy. I reworked the analysis in 2005 when I included these analyses in my book. The number improved slightly to about 1000. This does mean that within about a 500 light year period one such planet might exist. One thing that helps is that most of these 1000 planets if they exist do so in the middle to outer regions positioned comparable to where the sun is. This is based on metallicities. We might then be able to find it, though there are about a million stars in that region. I have not done the analysis since.

LC

lcrowell June 9, 2012 at 1:55 AM

This stems from my analysis of the stability of the solar system I did last decade. I ran long term numerical calculations of the three body problem of the Sun, Jupiter and Earth. I found that over a 10,000 year time period there was a drift of the Earth outwards. The orbit of the Earth on a short term basis vibrates about its orbit due to Jovian gravity. The periodicity is not exact, and so there is a chaotic drift that sets in. An analysis of these frequencies leads to a 1/f term that corresponds to this outward drift. This is why I think Earth was around .85AU at its inception and has drifted outwards since. This has kept the temperature on Earth relativity constant as the Sun has heated up over time. This should persist into the future as well, thus preventing a boiling up of the Earth environment in 500 million years and postponing that for a billion years or so.

I then extended this some. The 1/f drift corresponds to a Lyapunov exponent due to this perturbation. I then ran through the list of extrasolar planetary systems that had been found at the time. I estimated what would be the Lyapunov exponent for a planet around G-class stars at 1AU given the orbits of the known gas giants. I found only one extrasolar system which was somewhat close to the small value for the Earth. Most were much larger, which means a terrestrial planet at 1AU would be heavily perturbed and would not likely exist in a stable orbit. I then did a Bayesian analysis to estimate how many stellar systems might support a planet at 1AU with an outwards drift comparable to Earth. Initially I found that maybe a few hundred would exist in the whole galaxy. I reworked the analysis in 2005 when I included these analyses in my book. The number improved slightly to about 1000. This does mean that within about a 500 light year period one such planet might exist. One thing that helps is that most of these 1000 planets if they exist do so in the middle to outer regions positioned comparable to where the sun is. This is based on metallicities. We might then be able to find it, though there are about a million stars in that region. I have not done the analysis since.

LC

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Torbjörn Larsson June 6, 2012 at 8:18 PM

Testing hypotheses is never a waste of time. Now knowing, which an unfounded claim such as yours on ETI amount to, is certainly a waste of time.

And I say that as one who hypotheses that life naturally will expand to pervasive but unnoticeable forms of biospheres out there (EM silent Oort cloud colonization waves). Still, that needs to be tested like in this instance.

JamesNCleveland June 5, 2012 at 6:04 PM
sangos June 5, 2012 at 6:21 PM

As i read somewhere, our ‘high tech’ VLBI stuff might be like trying to detect smoke signals from advanced civilizations. These guys could be like the predator in the Schwarzenegger movie, who self pack nukes in don’t ask where.

ikma June 5, 2012 at 6:27 PM

I we were to put radio telescopes at the L4 and L5 points, and combine them with radio telescopes on earth, can we say what the potential resolution would be?

By which I mean, how far away could an earth-equivalent (in terms of radio output) planet be and still be confidently detectable?

Zoutsteen from Holland June 5, 2012 at 8:20 PM

I don’t know the math, but there are two different things to be aware of:
1) Resolution: Requires dish separation
2) Signal strength: Requires dish surface area

In other words: two small satelites won’t get the job done which an earth side dish or dish field can also do. But those same two satelites could study strong signals in higher detail.

On earth, dish surface area is artificialy created by using multiple dishes of smaller size. Note that there is now also a plan active to create a large baseline observatory, of which 1 part will be in Australia and the other in South Africa.
see: http://www.universetoday.com/95430/ska-the-worlds-largest-telescope-will-be-built-at-two-sites/

ikma June 5, 2012 at 8:33 PM

ok, so would it be possible to artificially create a large dish at L4 and L5 by flying a ‘fleet’ of three, four, or five smaller satellites spread out over some distance at each point?

krenshala June 5, 2012 at 9:40 PM

Leaving out technical details (and difficulties) – Yes, you could create a VLBA “dish” using multiple satellites at the L4/L5 (or other) points.

Torbjörn Larsson June 6, 2012 at 8:41 PM

Planetary Resources may have to make small radio satellites after they have succeeded in the optical satellite market!?

krenshala June 5, 2012 at 9:40 PM

Leaving out technical details (and difficulties) – Yes, you could create a VLBA “dish” using multiple satellites at the L4/L5 (or other) points.

Thomas Houck June 7, 2012 at 4:38 PM

Humans have only existed for a few brief seconds on the age of the Earth clock and for even less time on the age of the Universe clock. The time we have been able to emit radio signals would barely register on these two clocks. Now, apply that to us trying to detect signals from other intelligences and you are basically try to find a microscopic needle in an acres sized haystack. I have no doubt other intelligences exist and are, or have been out there, but at what stage of development. Intelligences that may have reached our level may have long ago come and gone or have yet to reach that level. To assume all intelligences would reach the point we are currently at, at the same time, is naive to say the least.

Geral Bassham June 14, 2012 at 9:35 AM

E T you might see him or her in your own town blending in . next time gary and I have contact we are going to send an invite to dinner . no kidding

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