Thursday, June 17, 2021

Why 'Oumuamua is NOT an "Alien Probe," and Why SETI Will "Fail"

The first object in our solar system confirmed to have come from interstellar space was discovered in 2017. It was named 'Oumuamua. And of late there has been a lot of talk that the object is really an alien probe, sent here by some distant intelligent species. Harvard astrophysicist Dr. Avi Loeb has outstanding scientific credentials, and of late he has been promoting that idea. In fact, he has written a book Extraterrestrial, calling 'Oumuamua "The first sign of intelligent life beyond earth."
As you might imagine, this has generated considerable interest among the public, turning Dr. Loeb into something of a celebrity (although many astronomers are still scratching their heads, as if to say, "What has gotten into this guy?")

Not a lot has been written critiquing the claim that  'Oumuamua is an extraterrestrial probe, but Dr. Ben Zuckerman, of the Department of Physics and Astronomy at UCLA (retired), was kind enough to send me some papers.

Dr. J. I. Katz of the Department of Physics and McDonnell Center for the Space Sciences, Washington University, St. Louis, Mo., has written a paper,  ‘Oumuamua is not Artificial. He writes [references removed here, see original],

Recently, the popular press has discussed the hypothesis, promoted in a popular book  that ‘Oumuamua, the interstellar object that transited the Solar System in 2017, is the product of an “alien” civilization, presumably reconnoitering the Solar System, rather than a natural fragment (a “Jurad”, an asteroid or comet nucleus) that escaped from an extra-Solar planetary system. There are several reasons why the alien civilization hypothesis is not credible
Katz notes that 

‘Oumuamua had a velocity, far from the Solar System but with respect to it, of about 26 km/s. The smallest credible distance of a sending civilization is about 10 light years (this volume contains 10–20 stars, enough that if all the possible optimistic assumptions are made it might contain an advanced civilization; the closest extra-Solar star is about 4 light years away). The transit time from that distance would be about 100,000 years. A decision to launch toward our Solar System must have been made about 100,000 years ago.
In other words, when ‘Oumuamua was traveling through interstellar space toward our solar system, its speed relative to the sun was only 26 km/sec, a bit slower than the earth's orbital velocity around the sun. We don't know where it originated, but it must have been traveling for hundreds of thousands, if not millions, of years. Clearly, if aliens constructed and launched 'Oumuamua, they were in no hurry whatsoever to see what it might discover.

Katz also notes that 

A flyby is an inefficient way to collect data and an unreliable way to attract notice. As our space programs know, if you want to collect information about a body, send an orbiter or a lander. There is no compelling argument against the presence of artificial orbiters in the Solar System, or against landers on any body other than the Earth. ‘Oumuamua was neither.

After traveling for many thousands, if not millions, of years, instead of going into orbit aroung the sun (or, better yet, the earth!), ‘Oumuamua just slid out of our solar system exactly as it slid in, behaving like a dumb rock.

Following up on this line of reasoning, Dr. Ben Zuckerman wrote a paper, ‘Oumuamua Is Not a Probe Sent to our Solar System by an Alien Civilization. Referring to a paper written by S. Bialy and Loeb on 'Oumuamua, Zuckerman notes,

other than implicitly assuming that extraterrestrials would want to send such a probe, their paper contains no discussion of the alien’s motivations. More than 50 years ago, the distinguished physicist Freeman Dyson understood that ignoring the question of motivation would be a huge mistake: “The problem of interstellar travel is a problem of motivation and not of physics”

Zuckerman suggests that, rather than sending probes like ‘Oumuamua is supposed to be, intelligent civilizations can obtain better information on nearby planetary systems, and much more quickly, by building large space telescopes:

Large space telescopes should permit detailed study of nearby planetary systems. It will be possible to obtain orbital and spectroscopic data of a quality comparable to that now obtainable from ground-based telescopic study of planets in our Solar System...

First generation planet-hunting space telescopes such as NASA’s [proposed] Terrestrial Planet Finder (“TPF”) or ESA’s DARWIN, would be able to discover “living worlds” such as Earth. This would be accomplished through identification of “biomolecules” in the planet’s atmosphere. Once such a world is found, then surely larger, more powerful, space telescopes would be constructed to resolve the planet’s surface well enough to reveal continents and oceans, the spectrum of “vegetation”, and variations in these as a function of time, both in the short-term (annual seasons) and the long-term (ice ages, or whatever). 
Zuckerman concludes,

we demonstrate that there exists no plausible reason why a technological civilization would build and launch ‘Oumuamua type probes of the sort described by Bialy & Loeb. The fleeting capabilities of any such flyby probe are vastly inferior to the power of space telescopes operational for eons of time in the interplanetary space of the alien civilization....

The Breakthrough Starship Project

Avi Loeb's proposed Breakthrough Starship project

As an appendix to his paper on 'Oumuamua, Dr. Katz includes a critical analysis of what is called The Breakthrough Project, a proposal suggesting that "it may be possible, using the radiation pressure of a laser, to accelerate a low mass spacecraft to semi-relativistic speeds for the purpose of interstellar reconnaissance." When I first saw this, I didn't understand why it belonged in this paper. Upon looking more closely, I soon saw the reason: this proposal is the brainchild of Avi Loeb. I find it ironic that Dr. Loeb, who is so cognizant of the need to achieve relativistic speeds if we wish to send out interstellar probes, is nonetheless willing to accept the interstellar tortoise 'Oumuamua as likely being of alien construction.

Katz notes several "insuperable problems" with the proposal, not the least of which is that "the sail will vaporize." His critique of the proposal is highly technical, and involves a whole slew of equations. But if Katz is correct, the proposal to accelerate an interstellar sail using lasers simply won't work. 

Extraterrestrials - Where Are They?

I first met Ben Zuckerman back in 1975 when I interviewed him to write an article about his SETI project, called Project Ozma II. My article appeared in Spaceflight magazine, a publication of the British Interplanetary Society, in the December, 1975 issue. The original Project Ozma was carried out by Dr. Frank Drake in 1960 using the 85-foot radio telescope at the National Radio Astronomy Observatory. It examined two nearby solar-type stars, Tau Ceti and Epsilon Eridani . The second Project Ozma was carried out by Zuckerman and his colleague, Dr. Patrick Palmer of the University of Chicago. They used the much larger 300 foot radio telescope at that same observatory, and intermittetently monitored 670 nearby stars from 1972-76. Despite gathering much more data using much more sensitive equipment than the first Project Ozma, no signs of intelligent signals were detected.

Michael Papagiannis, Benjamin Zuckerman, and
Michael Hart at the Where Are They? Conference, 1979.
But in certain circles, disillusion with SETI was setting in. On November 2nd and 3rd  of 1979,  Zuckerman and SETI critic Dr. Michael Hart of Trinity Univeristy, sponsored a conference at the University of Maryland (where Zuckerman was then teaching) titled Where are They?, to examine the famous "Fermi paradox": If alien life is so abundant, then where is everybody? What explains the absence of extraterrestrials on earth?

Many distinguished scientists participated in the conference, including physicist Freeman Dyson, radio astronomers Ronald N. Bracewell, Michael D. Papagiannis, and Sebastial von Hoerner, chemists Robert Shapiro and Cyril Ponnamperuna, and many others. I was invited to address claims that exterterrestrials are actually being seen in earth (i.e., UFO sightings). James Oberg spoke about the possibility of "terraforming" planets to be earrthlike, and thus supporting life. The proceedings of this conference were published as Extraterrestrials Where Are They? (Pergamon Press, 1982). 

Yours Truly with Freeman Dyson at
the Where Are They? conference.

An interesting anecdote from that conference: When we broke for lunch that first day, I was headed out with James Oberg and another participant. Oberg noticed Dyson wandering about somewhat aimlessly, and invited him to join us. So we all drove off to a nearby restaurant I knew. As we chatted during lunch, Dyson made a reference to 'my friend, a very brilliant man, Immanuel Velikovsky' (who at that time was still living, but died soon afterward). Both Dyson and Velikovsky lived in Princeton, New Jersey, and apparently they were good friends. I said to Dyson, 'Surely you don't believe Velikovsky's claims that Venus was a comet ejected from Jupiter, that passed by earth and dropped Manna from Heaven on the Israelites, and so on?' He replied, 'Of course not, that is just nonsense. But my friend Velikovsky is a brilliant man!' I didn't know what to say to that.

Why SETI Will "Fail"

In 2002, Zuckerman wrote a paper published in Mercury, the publication of the Astronomical Society of the Pacific, titled Why SETI Will Fail. The original paper is not on-line, but the text is available here. As in Zuckerman's paper above, large space telescopes, using principles of interferometry, play an important role in this argument.  Here is the Abstract in full:  "The union of space telescopes and interstellar spaceships guarantees that if extraterrestrial civilizations were common, someone would have come here long ago."

Dr. Zuckerman explains,

According to the timetable envisioned for NASA’s Terrestrial Planet Finder (TPF) mission, in the next 20 years we should witness the deployment of space telescopes capable of spotting Earth-like planets orbiting nearby stars. As currently conceived, these telescopes will be able to measure mid-infrared spectra of planetary atmospheres and detect molecules such as water vapor, carbon dioxide, methane, and free oxygen in the form of ozone. In other words, TPF will be capable of identifying life-bearing planets within about 30 light-years of Earth. When technology improves during the coming centuries, the range of such telescopes will no doubt be extended out to 100 or more light-years.

Unfortunately, NASA cancelled its Terrestrial Planet Finder mission in 2011. Although one realizes that the leaders on alien planets need not be as shortsighted as our own. Zuckerman optimistically explains, 

SETI endeavors should assume that any technological civilization within a few hundred light-years has had space telescopes capable of detecting and studying Earth for quite some time. If the typical technological civilization is 1 million years old, then such a civilization, if it lies within a few hundred light-years, has been studying us with its space telescopes for the past million years. This article will consider some implications of this basic idea....
But even if living worlds are not rare, SETI searches of stars within a tew hnndred light-years are doomed to fail because an advanced civilization on any nearby planet would have long ago employed space telescopes to identify Earth as a living planet and would have come to our solar system to investigate Earth. And once here, why leave?

So, to state Zuckerman's argument in its simplest form, if there were any advanced civilizations relatively nearby, they would have found us long ago, and probably have come here to explore. He explains,

Oxygen built up in Earth’s atmosphere about 2 billion years ago. Following that period, Earth could have been identified as a living world from afar. Any technological civilization that came within a few hundred light-years of Earth during the past 2 billion years would have had to choose between passively floating by (for a million years) and never learning about terrestrial life, or actively sending a spaceship to our solar system. Even if such an expedition took 1,000 years, this still would have been a very quick trip in comparison to a billion year wait for humans to show up with radio transmitters. During the past 2 billion years, millions of Sun-like stars have passed within a few hundred light-years of Earth, yet there is no evidence that technological extraterrestrials have ever visited our solar system.  This suggests that very few, if any, technological civilizations existed around these millions of stars.

This, he points out, is exactly the opposite conclusion reached by Carl Sagan and the other SETI optimists. (If so many advanced civilizations exist, then Where Are They?) Zuckerman argues that "Interstellar Travel Is Inexpensive":

sending a spaceship containing humans to another star will cost a lot more than sending a few astronauts to Mars. University of Illinois engineer Cliff Singer, in his excellent chapter ”Settlements in Space, and Interstellar Travel” in Extraterrestrials: Where Are They? (a book I co-edited with Michael Hart) estimates the cost of an interstellar spacecraft propelled by a stream of very high-velocity pellets. The estimated price is 1 million person-centuries (l million people each working for a century), or roughly 10 trillion dollars. Expensive? Not really, when one considers that this is about the cost of one decade of the worldwide arms race. Is human ”civilization” insane or what?
Various other forms of advanced propulsion systems are discussed in chapters by Freeman Dyson and Ian Crawford in Extraterrestrials: Where Are They?

But Zuckerman concludes,

While SETl skeptics may envision humans as possessing the most advanced brains in the Milky Way, nonetheless, it is we pessimists who are the true technological optimists...
Presumably meaning that it is our long-term destiny to spread out into the stars.



  1. Isn't there a contradiction in saying that our long-term destiny is to spread out into the stars, but that interstellar travel is virtually impossible? (as alluded to in your book?*). What technology can you envisage that would allow us to reach another star system in even 1000 years and that would let us perform more than a fly-by of a star or its planets?

    *in your book, were you alluding to routine and casual interstellar travel - of the type necessitated by proponents of the extraterrestrial hypothesis for UFOs - rather than interstellar travel per se?

    On 'Oumuamua: the Voyager space probes would take tens of thousands of years to reach even the nearest stars, yet they were launched with the romantic aspiration that ETs might some day intercept them and learn of our origin (admittedly, that wasn't their primary mission). 'Oumuamua need not be a probe designed to reconnoiter our solar system, but something that the aliens hoped would be intercepted by us. Would that not be a reasonable speculation?

    1. Well, I was explaining Zuckerman's argument, not necessarily promoting it.

      I have edited the text near the end to include an explanation of Zuckerman's argument where he says "Interstellar Travel Is Inexpensive".

    2. If Oumuamua is a Pioneer/Voyager analogue that "aliens hoped would be intercepted by us", then why disguise it as something entirely natural rather than obviously artificial like the Earth originated probes are?

  2. The Planetary Society hosted two scientists who produced a pretty convincing paper that posits that Oumuamua is a piece of a Kuiper Belt object. They discuss it on the Society's 21 April 21 podcast episode:

    I have not read Professor Loeb's book but based on another Planetary Society podcast interview, he seems to be backpedaling slightly from his starship" explanation. He now suggests the object is likely a piece of interstellar flotsam and jetsam, starship wreckage if you will. It appears to be his way of sticking to the artificial manufacture theory, while explaining the low relative velocity of the object. While he makes some excellent points about the hypocrisy of theoretical physicists celebrating ideas with zero observational evidence (String Theory, etc.), he does little to make his explanation more credible than the Kuiper Belt Object hypothesis.

  3. Regarding the Zuckerman quote at the end, might he have actually meant something like the following?: "While we SETI skeptics are extremely pessimistic about the existence of any other technological civilizations in the Milky Way, ironically we 'pessimists' are the true technological 'optimists,' i.e., it is we who are confident that any other advanced civilizations in our galaxy would by now have developed the technological means of making themselves known to us."


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