Identify the nature of 'Oumuamua – it's probably a comet, but …


Image of an alien spacecraft taken from the movie Encounters of the Third Kind.
Enlarge / I mean, maybe, no? May be? Probably not, though. Almost certainly not.

Shortly before Halloween, the chairman of the Harvard Astronomy Department openly declared that an interstellar object passing through our solar system might well be part of an extraterrestrial craft. And then … the crickets.

The astrophysics blog Centauri Dreams told the story to cognoscenti three days later. He presented an informed study of the academic paper that evoked this bold opportunity, reinforced by quotes and comments from the co-author of the paper (and chair of the department), Avi Loeb. It was fine in November before sales outlets like CNN, Time, and The Washington Post took up history, full of inevitable sarcastic quotes and sneaky headlines. The named object & # 39; Oumuamua, had a number of strange and seemingly contradictory properties; it may be that these properties appear so because our observations were not very good. There are also other possibilities.

I read Loeb's paper, which had been quickly accepted for publication by the respected Astrophysical Journal. A few days later, Loeb and I sat down for the longest and, after what Loeb says, the most serious and thorough interview he had at that time topic. The built-in audio player following the two dots at the end of this very sentence features an hourly edition of it, including all the highlights:

If you're not talking audio, we have a transcript available in plain text and PDF (which is probably a little easier to read).

"I'm not saying they are aliens, but …"

Avi Loeb is clearly poking around in one of the most extraordinary claims of astronomy. This, of course, requires extraordinary evidence – a requirement to which Loeb's fancy job title yields no exception. But we should also avoid the reflex reaction of the inverted-knee elbow, which looks like "Just because the chair of Harvard astronomy is saying it. could to be an extraterrestrial craftsman does not mean is a; and in fact, that means is not one, because the irony! Oh, and smugness, too. "

My interview with Loeb should not settle this extraterrestrial debate for you, for me or for anyone (Loeb himself needs more evidence to be able to consider the case as solved). But the story of Oumuamua is intrinsically fascinating. By digging in, non-astronomers can not help but learn about the workings of the Universe. If you follow this path, keep in mind that extraterrestrial technology has been taken into account and finally abandoned as an explanation for many astronomical phenomena. Oumuamua will probably join this list definitely someday. But we learn a lot by tracking down the tracks – both by the field of astronomy and by curious strangers who follow the process.

If you listen to our interview (or read our transcript probably-OK-ish), you'll understand this debate on a more subtle level than most people who talk about it. And the really cool thing? For the reasons we discuss near the end of our conversation, the big questions here could be solved dramatically as early as 2022, when a major new telescope will be put online.

For those in a hurry, I will now provide a summary of our interview, punctuated with timestamps to help you choose the parts that interest you the most.

There is something about 'Oumuamua

Our story begins on October 19th of last year (at the indicated time 7:55 from the interview audio above, if you wish to listen for more details than those contained in this brief description). It was at this point that the object that was going to be called "Oumuamua" was spotted for the first time by the Pan-STARRS system of Hawaii, which follows and detects objects near the Earth.

Astronomers quickly established that "Oumuamua was traveling too fast to be bound by our Sun, which means that it originated in a distant star system. This makes it the first interstellar object definitively identified in our solar system. Rightly intrigued, the astronomical community has pointed a lot of material towards the blip in decline. Masses of observational data were obtained before Oumuamua disappeared from sight in January.

Image of the artist representing the interstellar asteroid of strange shape - Oumuamua. "Src =" "width" = 640 "height =" 400 "srcset =" https: //cdn.arstechnica .net / wp-content / uploads / 2017/11 / 1I_eso_artistimpression-1280x800.jpg 2x
Enlarge / Artist view of the interstellar asteroid & # 39; Oumuamua & # 39; with strange shapes.

& # 39; Oumuamua was weird on many fronts from the beginning. An interesting point is that it moves to the "local standard of rest" (timestamp 3:36 p.m.) among our local stars. For the reasons explained by Loeb, it is a fascinating attribute – and unlikely (although not impossible) for a natural object.

In June (timestamp 11:22 p.m.) Nature has published a rigorous analysis of the trajectory of & # 39; Oumuamua. Its authors determined – with 30 standard deviations of confidence – that the object accelerated as it retreated from the Sun. This was interpreted as evidence that it was a comet rather than an asteroid (the other likely candidate). Comets generally accelerate in this way, propelled by gases released by the heat of the sun, which create their characteristic tail.

However, several observations go against this. (timestamp 25:44). For example, no tail has ever been observed on Oumuamua. Coma either (the fuzzy head of a comet). There was no sign of water on it, and comets usually carry water. And the surface reflectivity of Oumuamua is well beyond the cometary limits.

These quirks and others can be explained or justified by themselves. But for Loeb, the last drop was a September article by Roman Rafikov from Cambridge University (timestamp 28:39). He argues that "Oumuamua's rotational speed (which was quite high – another quirk) remained constant throughout the observation period, whereas the degassing should have considerably disrupted the rotation.

Loeb concluded that degassing would not have been able to cause the acceleration of "Oumuamua. He envisioned alternative forces and opted for a force that astronomers understand quite well: the pressure of radiation emitted by the sun. But it is a much weaker force than degassing. S & # 39; he was responsible, "Oumuamua should be much smaller than the number of rock astronomers of a kilometer and over considered. Specifically, Loeb identified it as not exceeding 20 meters in diameter. And – here is the tire – less than a millimeter thick.

Close encounters of one kind or another

No known natural process can produce anything so distant in space. But it looks a lot like a solar sail. And Loeb spent long hours modeling the physics of solar sails by participating in Yuri Milner's Breakthrough Starshot project (timestamp 6:55 p.m.). Yes, the cliché that hammer owners take non-nails for nails immediately comes to mind, and Loeb recognizes it (30:07). But hammers are also known to identify nails accurately.

The most exotic possibility in Loeb's paper (33:55) is that Umuamua was participating in a targeted reconnaissance mission (not necessarily selecting the Earth, but possibly traversing the habitable areas of the star systems). This is based on legacy calculations regarding the relative abundance of interstellar objects and other factors.

Loeb and I then discuss an online archive where he and his co-author, the post-doc Shmuel Bialy, initially file their article (36:58) and the unusual speed with which Astrophysical Journal both accepted and published (40:35). I then present to Loeb the critics of some of his critics, whom he answers (44:51). This leads to a discussion of Loeb's philosophy on the roles and responsibilities of academics.

The unusual approach of the object suggests that it would come from outside our solar system. "Src =" .22-PM-640x379.png "width =" 640 "height =" 379 "srcset =" 28-at-1.51.22-PM.png 2x
Enlarge / The unusual approach of the object suggests that it was coming from outside our solar system.

We conclude from the fascinating perspective that a large telescope starting in 2022 could quickly answer questions that are beyond the current material (56:56). This brings us back to the abundance of interstellar objects like "Oumuamua." If they are as rare as previous calculations, the new, more powerful machines will only discover a small handful. But though they are common enough to make discovering Oumuamua unsurprisingly, the new telescope should quickly spot thousands.

This argument is too complicated to be fully explored here (I am a podcaster, not a journalist). I invite you to listen to this section. All of this gives Loeb's controversial explanation a sell-by date, and that date is only a few years old.

Personally, I look forward to following the events closely. Listen to this section and you will know the underlying problems as well as me. No matter how thin, there is at least a small chance that 2022 provides suggestive evidence that suggests that "Oumuamua is an artificial relic. And whatever the outcome, would not it be cool to follow that story as it unfolds?

This interview is the most recent episode of my After On podcast. If you wish, you can find a complete archive of my episodes on my website or through your favorite podcast application by searching under the words "After On". The larger series is built around in-depth interviews with world-renowned thinkers, founders and scientists, and tends to be heavy in technology and science.

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