The canonical notion of the ‘water hole’ is that the kind of life we are looking for in our SETI searches will only thrive where there is liquid water. A quiet stretch of the radio spectrum, the water hole has two natural boundaries: The 18 cm emissions from the hydroxyl ion (OH) and the 21 cm emissions from neutral hydrogen. But the choice of frequencies for SETI is obviously not based on mere symbolism. The water hole is a window in the radio spectrum where radio emissions are not significantly absorbed by interstellar dust and other matter between the stars. It’s a natural place to look, and SETI@Home users worldwide have used Arecibo data from the waterhole to participate in the hunt, in what has turned out to be a massive distributed computing project.
But the latest SETI project to hit the news following the hibernation of the Allen Telescope Array last month goes where Arecibo cannot. This is a new effort at a storied place, the Green Bank facility in West Virginia. This is where Frank Drake launched Project Ozma back in 1960, although the UC-Berkeley astronomers behind the new effort will be using a new dish which happens to be the largest steerable radio telescope in the world. They’re going to work on 86 stars chosen from the 1235 candidate planetary systems thus far identified by the Kepler space observatory.
Image: The Robert C. Byrd Green Bank Telescope in West Virginia, the largest steerable radio telescope in the world, is observing 86 planetary systems that may contain Earth-like planets in hopes of detecting signals from intelligent civilizations. (Courtesy NRAO).
So why Green Bank and not Arecibo for this new hunt? In a word, location. The Arecibo dish is fixed and can’t observe the area of sky — covering the northern constellations of Cygnus, Lyra and Draco, well outside the ecliptic plane — that this search requires. Moreover, the scientists doing SETI via Arecibo are working around other astronomical observation efforts and they’re limited to the 21 cm area of the spectrum. The new effort hopes to extend that range, says Dan Werthimer, chief scientist for SETI@Home:
“Searching for ET around the 21 centimeter line works if civilizations are broadcasting intentionally, but what if planets are leaking signals like ‘I Love Lucy’? With a new data recorder on the Green Bank telescope, we can scan a 800 megaHertz range of frequencies simultaneously, which is 300 times the range we can get at Arecibo.”
The result: A single day on the Green Bank instrument produces as much SETI data as a year’s worth of observations at Arecibo, some 60 terabytes in all. The water hole is still in play but not a limiting factor in these efforts. Werthimer’s team will take an early run through the data, but SETI@Home users will put their processing power to work crunching the numbers in greater detail, an analysis that could take as much as a year to perform. It’s a nice touch that the software will indicate to users whether they’re working with Arecibo or Green Bank data as the Kepler hunt proceeds.
We need to get used to the relatively new acronym KOI — Kepler Object of Interest. The 54 candidate systems identified by the Kepler team as possibly being in the habitable temperature range — defined here as between 0 and 100 degrees Celsius, where liquid water can exist — are among the 86 stars chosen for the search, which includes other planets with orbital periods greater than 50 days and systems with four or more possible planets. Green Bank will scan these 86 stars individually but will also scan the entire Kepler field at the end of the search. And by the time SETI@Home has gone through this round of data, we should have a whole new batch of KOIs to contend with.
This is interesting and, of course, exciting – targeted SETI is an entirely new possibility. I don’t think we should give up more general searches, though.
For a start, there’s a fair amount of evidence from our own solar system that the so-called Goldilocks zone isn’t the only place to find liquid water and enough energy to drive biological reactions.
For a second, these “Goldilocks” planets are all circling red dwarfs (Paul, correct me if I’m wrong!). The intense magnetic fields in red dwarfs create spectacularly violent flares and CMEs. And because a “Goldilocks” planet around a red dwarf orbits really close in, it will get pretty severe radiations doses on a regular basis.
Neither of these is a deal-breaker because we simply don’t know enough about what constitutes an environment that is conducive to life. I am glad the study is going ahead – but these candidate planets are not necessarily as ideal as the media would have us believe.
Or maybe I have this wrong?
Richard
This is an utterly terrible definition of the habitable zone. It is fairly easy to show that the majority of the Kepler “habitable” candidates are more strongly-irradiated than Venus is. Essentially what the Kepler team have done is used the exact same method that led to claims of habitability for Gliese 581c despite it also being more strongly-irradiated than Venus: you would have thought they would have learned from such a well-publicised example! Furthermore even if constraining the effective temperature to a value at which water can be liquid were a valid method for defining the habitable zone, it is unclear why we should choose a pressure of 1 atmosphere to define the melting and boiling points.
Richard Burke-Ward writes:
Exactly so, Richard. See this story:
https://centauri-dreams.org/?p=17908
for example, and also note andy’s comment immediately above.
With hydrogen planets expanding the hab-zone outwards the focus on so close to the stars is naive.
The idea is not bad but……
Aren’t these just candidates awaiting confirmation ?
Isn’t radio telescope time an expensive resource to be allocated wisely ?
So why not do the scan AFTER confirmation ?
And possible after a proper habitability analysis too.
What is the maximum range at which the Byrd telescope at Green Bank could detect our own civilisation through “leaking signals like I Love Lucy”, and do all the 86 stars being examined fall within this range? If not, why do the SETI people think they’ll find anything?
Stephen
Oxford, UK
If we really want to find ETI, those worlds probably aren’t it. Mainstream SETI continues to play it safe for a variety of reasons. Time to start expanding the horizons, literally. Otherwise the SETI we have now will take forever to find anything.
What would the field of view for the telescope be at stellar distances? Wouldn’t it include planets far from their sun?
For sure, the concept of habitable zone doesn’t seem to be that reliable when considering the arguments mentioned above. Also, tidal effects might seriously impact the “habitability” of these planets.
Anyway, the search for alien intelligence can now also focus on stars where we know there might be planets, and this is definitely a great improvement.
Dan repeats the false Lucy Myth, i.e. that episodes of ‘I Love Lucy’ are being received by ETI. But an individual broadcast channel, with bandwidth sufficient to transmit video and audio, is undetectable outside our solar system. Nevertheless, the Lucy Myth is often mentioned, in fact encouraged, in the media and public talks about SETI, by speakers who know better.
This is similar to the ‘Arecibo Myth’, i.e., that Arecibo (Earth’s largest radio telescope) would be able to detect its hypothetical twin across the Galaxy. Arecibo can’t realistically communicate with another Arecibo over such distances. Those who so claim do not state their assumption that the bandwidth will be extremely narrow (0.01 Hz), that both the receiver and the transmitter will stare exactly at the right very small part of the sky, tracking each other, and that the receiver will track for hours in order to integrate a very weak signal and that no information will be sent. This last point is that, because the bandwidth is so small, the bit rate is glacial, far less than the slowest modem, maybe a bit per hour in the best case. Paul Shuch pointed this out 15 years ago, but SETI advocates keep repeating it, assuming that no one will do the calculation and see through it.
Jill Tarter’s analogy about a glass of water also reduces interest, as it makes the search seem hopeless.
Propagating myths makes SETI look less like a science, so may contribute to reduced funding for it.
So, Astronist is correct in questioning the detectability of leakage. Richard Burke-Ward: Targeted SETI is an hardly a new possibility. Most SETI work has been targeted toward the nearby stars.
Shoudn’t the range of liquid water go from the melting point to the critical point of water? 100 C as the boiling point is arbitrary, dependant on air pressure.
@Tom Mazanec: the critical temperature of water is 647 K, which is the highest temperature at which water can be liquid. The Kepler team calculated their planet temperatures by assuming uniform redistribution of energy over a sphere with albedo 0.3 and emissivity 1. (This is despite the fact that the paper states an emissivity of 0.9 and a redistribution over 62% of the surface which leads to different temperature values from the ones actually published, but that’s another story…)
Using this model and solving for the distance at which the effective temperature of the planet equals critical temperature of water puts the inner boundary of the habitable zone at 0.155 AU. For comparison, the planet Mercury (famed for its lush jungles and extensive oceans) has a perihelion distance of 0.307 AU.
The outer boundary of the habitable zone in this model would thus logically be the triple point of water (273.16 K). This implies the outer boundary of the Sun’s habitable zone is at 0.870 AU, well inside the orbit of the frozen wasteland that is the planet Earth, and comfortably beyond the orbit of the verdant garden world of Venus.
Yes, oceans of pure distilled water. Think it through.
Any SETI is better than no SETI. But not much is being or has been done. If talking about SETI could somehow equate to doing SETI we’d probably be on to our 3rd ET discovery by now.
OK, don’t thin Lucy, think RADAR. How bright would that sort of “leakage” be? Splain that.
These next paragraphs are modified from a post I made on Athena Andreadis’ Starship Reckless blog today. It fits in to how I feel about this latest SETI effort.
Virtually none of the alien worlds Kepler has found, bountiful as they have been over all previous exoplanet discoveries, are actually close to anything Earthlike or even near in size to our planet. Obviously I cannot say definitively whether there is life on those places or not of any kind, but it seems questionable that the relative handful of worlds which Kepler detected would also just happen to have ETI that possess radio technology and are signalling us.
Maybe there is a spaceship or two from some other solar system ala Star Trek exploring one of those systems and they decided to do a little METI while there, but I think you see what I mean.
Mainstream SETI needs to focus on other places in addition to Sol-type systems such as big infrared sources out on the galactic fringes where it is very cold and in the comet and planetoid belts of our Sol system. They also need to expand their search range beyond radio and optical, though I know the latter has only recently just gotten into vogue after years of unwarranted rejection by the mainstream SETI community. Just ask Dr. Stuart A. Kingsley what he had to go through to get Optical SETI accepted by the radio folks, or see his Web site at http://www.coseti.org.
Between all this, the recent “hibernation of the ATA, and the fact that we are really still just fancy animals, no wonder we haven’t found other minds yet or why they aren’t saying Hello to us.
With all this talk of optimal targets for SETI I cannot help but start to think from the sending ETI’s viewpoint. To me the only sufficient reason to justify the sending of a powerful unsolicited signal is because the potential recipients would have reason to suspect that that time and sky location would be especially privileged to the receipt of such a signal. That made me wonder how often one star within our galaxy would gravitationally lens another, and whether we should target these occurrences.