Don’t Talk to Me About a Face on Mars

I couldn’t decide which paper to discuss this week, so I’m talking about both. One made me think, the other made me angry. I suspect that this was the intent of the assignment.

Solar system artifact SETI might be one of the most giggle-inducing subsets of SETI. This seemingly wasn’t always true (throwback to the Martian “canals”), but it suffers from a series of issues. One is that there is a popular misconception that the solar system is a relatively well-explored piece of “territory” and we haven’t found anything yet. So solar system artifact SETI, in that light, seems antiquated. It always surprises me to learn how little we know as I progress through my education, and I think that feeling is relevant here. In addition, solar system artifact SETI makes SETI seem so close to home that the only conceptual guideposts people have are (generally cheesy and terrible) science fiction. Where a remote detection or a long timescale exchange of radio signals would be distant, sterile, and narratively boring, the discovery of an alien probe in the solar system or a city and giant face on Mars feels like fiction, so it’s treated as such, instead of legitimate science.

Now, to the articles!

The Freitas paper very logically stepped through the process of finding an answer to the question “which surveys on which parts of parameter space would have to be performed to disprove the existence of probes in the solar system?”. I take issue to a couple of framing assumptions that Freitas makes. Firstly, I don’t think it’s reasonable to assume that any probes we would find would be made for a neutral-to-discovery purpose (because we would’ve found one already if it wanted to contact us and we’d never see it if it was trying to hide, the logic goes). I can imagine many exceptions to this idea: a probe that was meant for communication but was damaged, a probe that is trying its best to contact us but by a method that we don’t have access to yet (perhaps on purpose, so we only see it at a reasonable point in our technological development), or a probe that was only partly for communication (mostly for another purpose, with only minor energy put into a beacon). The other thing that bothered me is that all of the constraints for the observational probe were constructed under the assumption that the probe wanted to observe Earth. That looking at a habitable planet, and that having the resolution to watch civilization arise on it, were valuable to our hypothetical watchers. I think that’s a bit anthropocentric – it could very well be that our asteroid belt is absolutely fascinating and ugh look at the primitives mucking up that third planet, they’re everywhere in this sector.

All of that said: you can’t do this work without making some assumptions to reduce the scale of the problem, and these were relatively minor ones. I loved the structure of the paper: consider the construction and purpose of the probe, then consider where it could be placed, note previously completed searches and their incompleteness (chock-full of references), then look at detection probabilities with current instruments and reasonable times. This is a methodical and scientific way to go about the stated problem in the paper.

The Carlotto paper, on the other hand, was rage-inducing. It would take a very, very convincing landscape artifact for me to feel comfortable announcing a “non-natural” origin. If Europa was covered in a giant swastika a la Armada (Ernest Cline’s less successful follow-up novel to Ready Player One), that would probably be sufficient. The 3D face is reconstructed from only two relatively low-resolution images, which makes me uncomfortable. The feature has since been imaged from other angles (by, among others, the Mars Global Surveyor) and, spoiler alert, doesn’t actually look like a face.

This is an example of textbook pareidolia: humans have a tendency to see patterns in random data, especially and specifically faces. Being good at recognizing and reading faces is vital for a social creature like a human being, so better to have some false positives than to accidentally mistake one’s significant other for a coat rack. But a base and known brain-stem bias like this should NOT cause us to write horribly misleading papers about the possible existence of an extinct Martian civilization. I don’t know how couth it is to consider the political ramifications of other people’s research, but it’s frustrating to see a vibrant and important sub-field continually shooting itself in the foot with scientifically sketchy bold claims and over-speculation from a few members of the community.

/endrant

The face of a facies: when a face is just a (rock) face

In 1976, the Viking spacecraft orbiting Mars took a picture. Well, it actually took many pictures, but there was one of particular interest to some people at Goddard and then the general public. This picture shows a structure that looks kind of like a human face:

The paper originally suggesting this feature looked like a face was originally dismissed for a few reasons, but people did continue to study it. Carlotto (my guess is for his own curiosity and for the interest of the public) performed a fairly extensive analysis of the image above along with one taken 35 orbits later. He cleaned up the data as best he could and then, using the two images, attempted to make a 3-D reconfiguration of the rock to see if the features persisted. I must say, I am fairly impressed with this paper. Carlotto only presents his opinion, that the feature might be artificial, near the end of the paper and only in one sentence. During the rest of the paper, he focuses mostly on explaining his methods and analysis.

I would say that his only flaw would be trying to pull too much information out of his crappy data. I also feel he should have used the other two images (although low resolution), because two data points is simply not enough to make a proper 3-D model of anything, especially if they two data points are from roughly the same angle at roughly the same time of day (Mars day). His 3-D model results (which he displays from different simulated camera positions) look near exact to the original image:

I agree with the original non-believers though. We humans are great at finding faces in just about any kind of rock:  Old Man of the Mountain, the Romanian Sphinx, the Pedra da Gávea, the Old Man of HoyStac Levenish, and the Badlands Guardian.

For anyone interested, here’s what the face looks like when you have nice data:

I mean, it looks really neat! It is still a nicely shaped, elliptical-ish mound. There even appear to be sand-drift (or maybe water) channels running off it. It just definitely looks like a rock though. This picture is courtesy of the Mars Global Surveyor from 1996.  The Mars Reconnaissance Orbiter (2005) also imaged this area, but it looks about the same as above: no face. And this kind of makes sense! If life were to take as long to arise on Mars as it did on Earth (which hopefully would have occurred when it was still wet), then any civilization would have been recently died out, and anything they left behind would be visible yet subject to weathering. With its sad atmosphere and lack of water cycle, Mars no longer has as much weathering as it maybe did at one point, but any “face” made by a civilization would not last. (Also, who would make a mile long face?? At least our large structures on Earth are visually appealing when you’re next to them and don’t require spacecraft to admire.)

Is It a Megastructure? (No)

The G-HAT papers have definitely been dense reading. I think Part IV (the paper I’ll be discussing in this blog post) has been the most accessible one to me so far.

My favourite table/figure in this work is simply Table 1, so I’m going to talk about it a lot.

The aforementioned Table I

Firstly, I think it encapsulates the fundamental challenges in artifact SETI: 1) the artifact has to exist and 2) we have to be able to tell that there’s an artifact. This sounds simple, but I think is a useful comparison to the fundamental challenges in communication SETI: 1) the (intentional!) signal has to exist and 2) we have to be able to tell that it’s a signal.

Secondly, it’s good to keep perspective in SETI research: not every anomaly is ETI. In fact, all of them so far are not. The table illustrates that for every megastructure-y looking object, there are reasonable (and plausible) “natural confounders”. This makes sense; though we’re trying to wring as much information out of a single lightcurve as we can (and we’re quite good at it – we can even tell the full 3D stellar rotation and planetary orbit geometry) it’s still just a lightcurve, and there are many inputs that produce the same output. Perspective is vital, especially in a paper that is ~hunting for alien megastructures~

Thirdly, I just love lists, as you can probably tell by the way I write my blog posts. The section following the table goes through the six physical “Distinguishing Features of Megastructures” (ex. anomalous masses, aspects, or orbits).  The section after that talks about the nine physical “Confounding Natural Sources of Megastructure Signatures” (ex. starspots, ring systems, or non-transited stars in the field of view aka. “blends”). I’m italicizing the word physical to illustrate exactly what it is that I like about the structure of this section: it shows what distinguishing properties of the systems being observed would be visible to an observer within the system. But we are not within the system – we’re working from lightcurves. And that’s where Table 1 comes in: showing exactly which of the physical properties discussed in (perhaps agonizing) detail would cause which of the 10 lightcurve anomalies in the Table.

I will now briefly summarize the rest of the paper, which I found generally less interesting to me. The next section talks about a few objects in particular that show some of the transit anomalies discussed in the previous section. The section after that discusses how to distinguish a signal beacon from a constant source from an information-rich signal by doing statistical analyses in both the frequency and time domains. The authors quantify it with a “normalized information content statistic”.  I’ll admit that the methods in this section were mostly over my head, but I think (hypothetically) that the uniform application of them to future SETI studies would be a fruitful pursuit.

I’m Conflicted About Artifact SETI

I’m going to frame this blog post into “pros” and “cons” of artifact SETI, with a lot of references to three specific papers we read about searching for extremely advanced ETIs(Annis (1999)Carrigan 2009, and Wright et al. 2014b).

Pros:

  • No dealing with Schelling points!
  • No making assumptions about xenopsychology and alien motivations!
  • No need to even consider a METI approach!
  • This is actual, performable, observational astronomy.
  • Huge budgets aren’t needed. Carrigan (2009) used IRAS sources which had already been catalogued.
  • Actual constraints can be placed. Annis (1999) made a (perhaps arbitrary) statement that no galaxy out of his ~130 galaxy survey had a Type III civilization harvesting 75% or more of the available stellar energy.
  • Interesting objects can (and will) be found during the search for outliers, which is far less likely in communication SETI. Carrigan (2009) found 16 objects which were (weak) Dyson sphere “candidates”, which mostly indicated an unusual IR signature.

The Con:

  • We can only look for extremely advanced civilizations, because we need the artifacts themselves to be detectable by our technology at interstellar and even intergalactic distances. The three papers we read for this week were all focused on Kardashev Type II or Type III civilizations. The sheer enormity of lengths of time involved versus (assumed) civilizational lifetimes means that we’re way more likely to come into contact with a civilization more advanced than we are than one at about the same age. But the idea of searching for them makes me a little squeamish.

Any astronomer can tell you that the distance scales of space are not really built for/intuitive to humans. I personally find that there’s a sort of intellectual harmony in the thought that interstellar travel is just hard and not worth it (not quite in a Hart sense of “physical explanations”). Though the swan songs of “free” energy, FTL travel, and the use of dark energy are tempting, and the excuse of poorly understood current physics convenient (as discussed in Wright et al. 2014b), that doesn’t mean they’re necessarily rational fallbacks. Much of our ideas about how galactic settlement would work are based more on the ideas of settlement from Earth’s history, and though it feels tempting to just zoom out and apply the same metaphors, there are fundamental differences that to me* feel insurmountable.

All of that to say: I don’t find it very intellectually fulfilling to do artifact SETI for Type II and Type III civilizations, Type III civilizations especially. It’s too much speculation. So while Annis makes conclusions about the frequency of Type III civilizations, I don’t find his results particularly compelling or surprising.

*at this point in my education, perhaps I’ll look back on this and laugh

 

We are too young for that!

Nikolai Kardashev, in his seminal 1964 paper, classified civilizations into three broad categories:

  1. a civilization with technological level close to that presently attained on the earth.
  2. a civilization capable of harnessing the energy radiated by its own star, and
  3. a civilization in possession of energy on the scale of its own galaxy.

Even since this publication, people have hypothesized different methods of detecting alien megastructures (see Figure 1 for examples). A feat of extensive galactic engineering (e.g. through many Dyson spheres) would be readily discernible in the spectrum of an object. At least this was the hypothesis for the Fermilab astrophysicist James Annis when he undertook a search for class III Kardashev civilizations. Annis argued the “most direct way to obtain power” for type II and III civilizations would be to harness stellar power. This would imply the interruption or redirection of starlight which, when performed on a galactic scale, should produce an observable change in a galaxy.

Figure 1: The Hunt is on!The search for alien mega structures! Some have argued we should use the transit method to detect transits inconsistent with a planet. Others have argued artifact SETI should focus on the thermodynamic evidence. This often means one Dyson sphere covering a star or a galaxy full of Dyson spheres. Annis himself was looking for galaxies modified by type III civilizations, such that the redirection of optical light would result in significant dimming which would present itself as an outlier on scaling relationships. Source: New Scientist

Annis made a distinction between natural galaxies and those that have been modified by a type III civilization. Galaxies are bound by their masses such that there exist gravitational-thermal scaling relationships. To derive the fundamental scaling relationships, Annis used the virial theorem and assumed the temperature of the galaxy was defined by the random velocities of its stars (e.g. similar to an ideal gas). He derived a generate relationship between the radius of a galaxy, R, the surface density, I, and the temperature, T, such that T=CIR, where C is a constant. In practice, the relationship he derived is not that simple but does emphasize that (i) self-gravitating systems have a simple relationship for R, I, and T and (ii) a natural, unperturbed galaxy shows such relationship. The relationships he uses are the Tully-Fisher relationship for spiral galaxies (LIR2) and the fundamental plane for normal elliptical galaxies (RT0.68I-0.85) and he notes a small scatter of ~10%.

Given that the relationship between these parameters was relatively consistent, this allowed Annis to look for outlier galaxies in each trend. His argument was that a type III Kardashev civilization would be “an outlier on R-I-T relations in the sense of anomalously low I, probably with a thermal IR excess, and possibly with a low surface brightness in absolute terms”. The results of his search through 31 spiral galaxies and 106 elliptical galaxies is shown in Figure 2. In this available sample, Annis found no candidate type III civilizations where at least 75% of the light would be dimmed. Annis attributed the null detection to various factors: his limit for outlier classification, instrumental effects, and potential bias against modified galaxies within current catalogs.

Figure 2: The data presented by Annis. The left figure shows the relationship for spiral galaxies while the right figure is for elliptical galaxies. The solid line is the best-fit relationship for the sample. The dashed line represents the limit of 75% dimness. Anything below (in the case of spiral galaxies) or above (in the case of elliptical galaxies) would be a likely candidate for modification by a type III civilization.

To this blogger, the most important thing is the limits Annis was able to place on the formation of type III civilizations. He presents one of the first attempts to statistically evaluate our isolation in the Universe. As a thought experiment, we can assume the appearance of a type III civilization follows a Poisson distribution (p=e-rT) and could occur at any point in time. Given that, on order, the galaxy’s age is 10 billion years, a 99% probability of a null detection would suggest an occurrence rate of r=4.61×10-10 per year or, equivalently, that it takes at least 2.1 billion years for a type III civilization to occur by chance. If each galaxy represents an independent realization of the thought experiment, then the upper limit on the occurrence rate suggests ~300 billion years must pass for a type III civilization to exist. Ergo, the Universe is too young for these civilizations.

The work by Annis suggests future searches for type III civilizations would be illogical. Future attempts have tried to address this. Most recently, Wright et. al. argue against the temporal argument raised by Annis. Wright et. al. agree with Annis in that his sample, derived from optical catalogs, may be biased against galaxies which theoretically have little to no optical emission. They also criticized the use of a random Poisson process and independent of time as this would presumably contradict the time-dependent evolution of life (e.g. from no life, to type I, type II, and finally type III civilization). Wright et. al. argue that a much larger sample, preferably in the IR, would serve as a better search, although any outlier found would still require significant vetting. Annis himself has pondered:

“Life, once it becomes spacefaring, looks like it could cross a galaxy in as little as 50 million years, and 50 million years is a very short time compared to the billion-year timescales of planets and galaxies. … Maybe spacefaring civilizations are rare and isolated, but it only takes just one to want and be able to modify its galaxy for you to be able to see it. If you look at enough galaxies, you should eventually see something obviously artificial. That’s why it’s so uncomfortable that the more we look, the more natural everything appears.”

As of now, there is no unambiguous detection of a type III civilization. This blogger is not particularly surprised by the null detection. Perhaps future searches will bear fruit, but for now the only thing for certain is that the Universe holds one type I civilization.

19 Years Ago We Didn’t Find Aliens

Surprise! Bet you didn’t know that.

In 1999, Annis performed a simple “search”  for alien life. He hypothesized (probably correctly) that a type III Kardashev civilization, one that controls power comparable to an entire galaxy, would be an outlier on R-I-T relations, where R is the size of the galaxy, I is the intensity, and T is the temperature. Both spiral and elliptical galaxies have such relations, Tully-Fisher for spiral and the fundamental plane for elliptical galaxies. He also theorized that such galaxies would have an excess of IR radiation and would have low surface brightness. Using data on 106 elliptical galaxies and 57 spiral galaxies taken more than a decade before he published his paper, Annis looked for any outliers in the above relations. He defined his outliers to be objects more than 1.5 magnitudes dimmer than the emission predicted by the respective relation. This seems fairly safe, and like a sound argument for detecting life. Personally, I don’t see any civilization becoming a type III civilization, so I consider this and related searches to be a decent waste of time (for SETI; some of the searches lead to important science).

Not surprisingly, Annis found no objects that met his outlier criteria. I say this isn’t surprising for two reasons. First, I feel that a galaxy with anomalously low emission would have been flagged prior to this search given how long the data were available. Second, this search was of so few galaxies. (A weak third argument would simply be that a civilization capable of eating up energy on the order of their galaxy would have ways of compensating for this fact, like Kipping 2015 suggested covering transits with lasers.)

This search to me just seems a bit useless and like he had a free afternoon and wanted to just quickly write up and publish *something*. Even if he were to find a galaxy with too low emission, it would require additional data in some other field to confirm it had anything to do with ETs. That being said, I would be interested in seeing someone do this with all the data we have nowadays.

Do Kardashev Type III civilizations really exist? (Annis 1999)

In this blogpost I shall review and briefly summarize the article by James Annis (1999) which is the first published work on the search for Kardashev Type III civilizations.

The 1964 work by Nikolai Kardashev established a scale for the technological development of intelligent civilizations based on their energy consumption. A Type III entity was posited to have the technological prowess to harness the energy of its entire galaxy. This would mean that it could capture energy from most of the stars in the galaxy and / or the supermassive black hole at the center of the galaxy. Potentially even Dark Matter and Dark Energy?

Annis theorizes that the if a entity could capture energy from most of the stars in its galaxy, it would give off signatures that should be observable by us. From the fundamental concepts of gravitation and thermodynamics he establishes relations between the observed intensity and the temperature of the galaxy.  These relations should hold true for naturally occurring signals from galaxies. Therefore a potential way to find these ET civilizations is to look for outliers.

The cultivation of energy from stellar sources would lead to a dip in the stellar flux at the peak of its black body and increased emission at about 300 K since the absorbing objects would emit in the thermal region. Using the Tully Fisher relationship they plot the Luminosity vs Rotation Velocity (proxy for temperature) of the galaxies and try to find outliers or deviations from the trend. Doing this for a sample of about 130 Spiral and Elliptical galaxies they do not find any signals which can potentially be attributed to a Type III civilization.

Citing the results of his work, and the fact that we see that our (and our closest) galaxy/ies do not show such an anomaly, he tries to put constraints on the incidence rates for such a civilization. The upper limit on this rate is calculated to be about 300 Gyrs, which effectively means that such civilizations do not currently exist. However, an interesting point raised is the possibility of observer’s bias in the sample collected, and the fact that the outliers in the trend might have been excluded earlier on.

Further, if their technologies have evolved beyond stellar energy to more advanced forms such as exploiting the black hole at the center of the galaxy or generating energy from dark energy or dark matter then this technique would fail.  This is further discussed in Wright et al. 2014b.

 

“Interesting” Statistical Techniques for Archival SETI

In Annis (1999), an archival data based search is conducted to see if any nearby galaxies display the characteristics of hosting an extremely advanced ETI. In particular, the paper looks for Kardashev type III civilization (one that can control energy on the scale of its entire host galaxy) that is converting most of the starlight in its galaxy into usable energy. Deflecting large amounts of starlight should noticeably dim the surface brightness of the galaxy and would show up clearly as an outlier in the well-documented galaxy relations. The author searches for these outliers in the brightness and temperature data from spiral galaxies in clusters and nearby elliptical galaxies. None are found.

One question I had while reading this paper was how would we know a dim galaxy were there? I mean, if almost all of the starlight is being blocked, then how would we even know to look at that place in the sky? Presumably, we would see a dim galaxy’s gravitational effects on its neighbors, which may have been why the study focusses somewhat on galaxies in nearby spiral galaxy clusters (Virgo and Ursa Major).

The author chooses a pretty arbitrary floor for what he thinks is an outlier. He decides that any galaxy that is 75% dimmer than its respective (spiral or elliptical galaxy) relation is an outlier. His methodology seems pretty circular though. He visually finds what he thinks is where, if one assumes there is Gaussian scatter about the relations, a cutoff is that is “at some high sigma enough to avoid statistical outliers”. There are certainly more robust ways to calculate outliers (including finding the Mahalanobis distances from each data point to the sample means).

An interesting calculation that is performed at the end of the article constrains the emergence time of a star-fed Kardashev type III civilization. Assuming that there is a constant chance of a KIII civ occurring throughout time, you can use Poissonian statistics and the fact that since it appears that all of the surveyed galaxies (including our own) have no KIII civilizations to put a lower limit on the occurrence time for these civilizations. Each new galaxy that they aren’t detected in adds ~10 Gyr of non-detection time. The paper arrives at a lower limit of ~6.5 billion years at 99% confidence. Neat.

 

Such Strong. Much SNR. Wow!

Kraus (1979) is about telling the story of the discovery of the Wow! Signal, arguably the strongest candidate for an ETI transmission detected.

The Ohio State University Radio Observatory holds the record for the longest ET search ever performed. Non-SETI whole sky radio surveys in started in 1965, but funding was cut abruptly in 1972 leaving a world-class telescope unable to perform large-scale operations. At this point, it was decided to use a previously-built detector to try to look for ETI signals in the “waterhole”. A couple upgrades and a lot of unpaid student and volunteer work later, the radio telescope was running ~full-time on a routine SETI program.

In August of 1977, the search paid off with the detection of a transient, celestial signal that caused discoverer Jerry Ehman to exclaim “Wow!” in the margins of the data print-out. Even though the same region of the sky was searched for weeks afterward, no new signals were found.

The article reads weirdly like an underdog sports story. I’m sure the back of the book would read something like “No funding, no precedent, and no excuses. Can these scrappy buckeyes go against all odds and find the interstellar connection that many believe impossible?”. This does make sense though as this is a magazine article, not a research paper.

Some obvious next steps (for the follow-up article, of course) would be to see if this region of the sky had been observed since then and report back either on the tragic lack of signal or the tragic lack of observation.

Searching for Ozma!

Princess Ozma?
No.   Project Ozma

 

 

 

 

 

 

 

The PSU SETI class with the Project Ozma 85ft telescope.

 

In his 1960 article for Physics Today, Frank Donald Drake (1930 – Now) discusses the rationale for searching for extra-terrestrial (ET) intelligent civilizations using radio surveys, and after doing so describes Project Ozma. Further, he lays the groundwork to quantify the probability of finding intelligent life, which was later formalized as the ‘Drake Equation’.

Project Ozma conducted at Green Bank using the 26 m (85 ft) diameter radio telescope, was one of the first SETI (Search for Extra-Terrestrial Intelligence) experiments to search for intelligent transmissions of ET origin. It included observations of Tau Ceti and Epsilon Eridani, two stars spectrally similar to the Sun. With the exception of a false alarm due to a secret military project, the project did not yield any significant signal from these two stars.

Drake starts off by discussing how later generation stars contain not only Hydrogen and Helium but also metals. These metals (heavier elements) are required to form solid bodies like planets. Further, the formation of planets assuages the angular momentum problem in a cloud of condensing gas. Sun and other stars like the Sun have relatively slow rotational periods. This rotational period does not conserve the initial angular momentum and hence leads to a discrepancy. This can be solved by the introduction of secondary bodies like planets or binary stars, to which the gas cloud transfers angular momentum as it slows down. Drake suggests that as high as 60 percent of stars should harbour planetary systems.

Establishing heuristic arguments for their existence, Drake goes on to hypothesize whether life can arise on these extra solar planetary systems. He then cites the Urey – Miller experiment, which managed to successfully create amino acids in the laboratory using gases like ammonia, methane, hydrogen and water vapour and an electric discharge (simulating the early atmosphere and a lightning discharge). Amino acids are the building blocks of proteins which are the key ingredients for life. Therefore, the oceans were the harbinger of early life, which after about 5 billion years of evolution led to intelligent civilization. Drawing parallels to the origin and evolution of  life on Earth, he postulates the fact that since life would take so long (5 Gyrs) to develop and achieve intelligent civilization one can discount non main – sequence stars and those which have relatively short life spans (stars much larger than the Sun).

Another consequence of the comparison to life on Earth is the hypothesis that life needs liquid water to develop, due to which the planet (if it has water on it), cannot be too cold or too hot. This leads to existence of a narrow band around the star a planet can orbit – The Habitable zone. Being much closer, or much farther would lead to the vapourisation or freezing of water, respectively.

To search for such life on Earth – like planets around Sun – like stars, the use of narrow – band transmission in the radio is suggested. Discovery, and subsequent contact with such a civilization would likely be in the vicinity of the 1420 MHz region of the radio spectrum. This would be because it corresponds to the 21 cm Hydrogen line spin transition in neutral Hydrogen, a spectral feature that should be known to an intelligent life form. Also, in this region the cosmic noise signal is negligible making it easier to transfer signal at cosmic distances. On the other hand, even if we want to actively seek out ET intelligence this would be the appropriate EM region to seek communication in, since there is a greater possibility of such civilization having radio telescopes tuned and actively searching in this region of the spectrum.

Thus Drake lays the justification for Project Ozma where he searches in this radio band around two Sun -like stars (for princess Ozma?) . He concludes by stating the goal (of finding ET  intelligence) justifies the amount of effort required to carry out this work, and with the hope that in the near future, the search will be successful.