The enigmatic ‘Oumuamua continues to stir controversy. Last week we looked at a new paper from Jennifer Bergner (UC-Berkeley) and Darryl Seligman (Cornell University), discussing a mechanism for the interstellar object’s unusual non-gravitational acceleration. The researchers explored the possibility that ice impacted by high-energy particles like cosmic rays would dissociate water in a comet to create molecular hydrogen within the ice. Was the warming of this hydrogen, all but undetectable according to the authors, the cause of outgassing and the anomalous acceleration?
Image: This very deep combined image shows the interstellar object ‘Oumuamua at the center of the image. It is surrounded by the trails of faint stars that are smeared as the telescopes tracked the moving comet. Credit: ESO/K. Meech et al.
Answering the question in a paper just submitted to the arXiv site is Harvard’s Avi Loeb, working with Thiem Hoang (Korea University of Science and Technology), who home in on Bergner and Seligman’s finding that the surface temperature of ‘Oumuamua can exceed 140 K at perihelion, enough to produce this evaporation. Loeb and Hoang argue that this calculation ignores the effect of evaporative cooling of the molecular hydrogen. The authors proceed to take such cooling into account and find that the surface temperature of H2 water ice is lower than that calculated by Bergner and Seligman by a factor of 9. This is turn reduces the projected outgassing.
From the paper:
…we found that the evaporative cooling is much more efficient than radiative cooling at temperatures above 20 K (see Figure 1, left panel). By taking into account the evaporative cooling by H2 evaporation, our results (see Figure 1, right panel) show that the surface temperatures of H2-water ice are lower by a factor of 9 than the temperature obtained by Bergner & Seligman (2023) (see their figure 3). Therefore, the thermal speed of outgassing H2 is decreased by a factor of 3.
Image: This is Figure 1 from the paper. Caption: Left panel: comparison of heating and cooling rates when the object is located at 1.4 times the Earth separation from the sun. Evaporative cooling by H2 is dominant over radiative cooling. The intersection of heating and total cooling determines the equilibrium surface temperature. Right panel: surface temperature at different distances, calculated for the case with (solid lines) and without (dashed-dotted line) evaporative cooling. Different ratio of H2 to water is assumed. Evaporative cooling by H2 decreases significantly the surface temperature compared to the case without evaporative cooling (dashed-dotted line).
And this is a problem for the molecular hydrogen evaporation scenario. The result of this decrease in outgassing is that ‘Oumuamua would have had to have been what the authors call an ‘oxygen iceberg’ to produce enough molecular hydrogen to drive the observed acceleration, a highly unlikely scenario for the following reason:
Given this constraint, the requirement for a surface layer that is made of pure molecular hydrogen will not survive the journey through interstellar space as a result of heating by starlight (Hoang & Loeb 2020). Moreover, the lower surface temperature also influences the thermal annealing of water ice, a key process that is appealed to by Bergner & Seligman (2023) to release H2.
The paper is Hoang & Loeb, “Implications of evaporative cooling by H2 for 1I/‘Oumuamua” (full text).
At least the paper stops at the analysis that is used to question, if not refute, the H2 outgassing hypothesis to account for the acceleration of ‘Oumuamua as it accelerated after perihelion. There is no false logic that therefore his alien ship hypothesis must therefore be the preferred explanation. Whether he strays from the science to his speculation in other forums is another issue.
I’m not qualified to really judge the paper or Dr. Avi Loeb’s reaction, and this isn’t really the platform to start a polemic, but doesn’t Dr. Loeb grift too much on the whole ‘it must be aliens’ shtick? It seems easier to fundraise on fantastical claims and although Dr. Loeb is a real scientist, I do get a bit of an ‘Ancient Aliens’ vibe about the way he operates, it’s almost more about picking a fight than real science…
Ivar, I was thinking those exact same thoughts.
Way too aggressive with his low probability speculations. His interaction on a SETI forum was embarrassing.
Oumuamua has a SOL relative speed of 26.32km/s. Present radial velocity calculates to 15.5km/s. The arms radial outward expansion is 59km/s (assuming a 10-degree orbit intercept). GEO-dating places the Orion final passage of SOL at 1 million/yrs. from now.
Ingress 26.34km/s measured at 2300 AU.
Egress 26.32km/s measured at 2300 AU.
Sounds to me like Bergner and Seligman need to address and try and refute Loeb’s analysis. Otherwise we have an interesting anomoly here, how else could it accelerate?
Not saying it’s aliens!
Debates like this are a philosophical tight rope, but in general Loeb has a good point: The scientific community could stand to be a little more self-consistent in its application of skepticism.
We know for a fact that artificial technology exists, because we make it. Ergo, it is a demonstrated phenomenon of the universe. We do *not*, however, know for a fact that the complicated mechanical structures of hydrogen being hypothesized for Oumuamua exist.
So Occam is not as simple for this question as some folks are making out.
Nevertheless, the Bayesian priors for this object being natural based on hundreds of years of astronomy are very high, and it being artificial very, very low. The default should be a natural explanation and then, when ruled out, should artificial hypotheses be examined seriously.
Right now it is dueling hypotheses – natural vs artificial.
To visit ‘Oumuamua would be very expensive. Is it worth it if the likelihood of it being entirely natural is very high?
+1 @alex
I would define it as a nice bonus if you get something unexpected as alien tech out of your research, but is the yield of the investment not higher if you keep to realistic objectives? Loeb seems to turn this principle around, which might earn him funding in the short term but isn’t this overpromising?
Also, is the focus on finding aliens or their tech really that satisfactory in the end? Communication would likely be none existent for millennia if found. And Aliens are out there, in our galaxy, it still might take us millennia to find them: the desire for a quick answer distracts from the objectives we have control over.
Finding evidence of alien intelligence, extant or extinct would be very important as it would change our views of life and intelligence in the universe. The only extraterrestrial beings we have today are mythical gods of various stripes, including at least one who made the universe. What a difference if we discovered a non-mythical intelligence, and what that means for life and technology in the universe. The ramifications would be many and likely great.
However, the way Loeb is going about it is bordering on History Channel alien “documentaries” territory. Unless he is truly successful despite the long odds, he will squander his reputation.
I recall a meeting at NASA’s Moffett Field about Mars, and they had a video link with Arthur C Clarke in Sri Lanka. He went off on structures that looked like [fossil] trees from the orbital images. While there wasn’t any audible tittering, he did his reputation no favors. It was just sad. Loeb could be similarly seen if he cannot back up his claims with solid evidence. As @Ron S says, the hypotheses are all rather weak, and it is like “duelling with limp noodles”. I agree.
The hypotheses are dueling with limp noodles. No one will be harmed but it’s also pointless. With such a notable paucity of data, no hypothesis can be elevated to a significant degree of certainty and few hypotheses can be eliminated. But I agree with you regarding the priors.
It would be interesting to have some scheme proposed in advance of the next interstellar object, where we consider the odds of any given trajectory and behavior for natural versus alien. For example, the probability of an alien ship entering the system and passing far from Earth seems lower than one passing close by. But the chance of a natural asteroid increases with distance from Earth, though perhaps not by something quite so easy as an inverse square. Of course, that flies in the face of creativity, which wants to break in and say surely this could have been an automated, almost-ballistic shipment between two alien outposts in our Oort cloud that care nothing about our scalding little sphere… how do you estimate the odds of that? It seems impossible: yet whenever you choose to launch – or don’t launch – a probe, you are indisputably estimating those odds.
Predicting the psychology of the aliens is a sticking point. What are the odds that these aliens do Manson Family style “creepy crawly” raids, deliberately finding ways to give us just enough evidence they have invaded our space that some people find a reason to wonder (like a 17 m/s acceleration comparable to a comet outgassing), while making sure never to be seen in any conclusive way? Yet that may affect our odds of launching a probe another way, because it is less likely to return conclusive data!
Maybe we should keep a powerful com laser or microwave transmitter in orbit than can send the next visitor a message as it flies past. If it is just a rock, no harm’s done. If there is anyone aboard, they’ll know we know they’re there.
This hailing beacon could have other purposes, so it would not be a waste of resources putting it here.
Unless its a derelict.
I would bet good money that objects like Oumuamua are natural. But if it is an alien space ship, then the hypothesis most consistent with its trajectory and behavior is that its a barely functioning wreck.
Arthur C. Clarke wrote one such short story in the 1950’s. We need a version for the 21st century!
Are you referring to “Passer-By” (in The Other Side of the Sky) [pub. 1957] ? A lovely set of very short stories. Also the set of stories in “Venture to the Moon” [pub. 1956]. All have that charm that is now lost to reality.
If a derelict, we would need to assume the solar sail never faced the Sun on approach. This is possible but, imo, a big ask. We could also posit that the sail was furled on approach and only opened partially, either as planned or as a consequence of being a derelict.
The solar sail hypothesis requires we make untestable assumptions about the mission architecture for the craft.
That sounds like alien behaviour consistent with Robin Hanson’s speculations on how ETI’s will behave if trying to impress us.
Hanson’s speculation requires the craft impress us. Mimicing a rock isn’t impressive. Imho, his speculation about the potential motivation behind UFOs isn’t strong. Because, supposedly, just one instance of leaving a home-world has a high probability of leading to inhabiting every system; these hypothetical ETIs send many missions off their home-world.
Questioning the assumption that space faring people inhabit every system is a more stable approach.
I apologize for making a half-baked comment, but I wanted to mention that one fact known about ‘Oumuamua is that it is red, most plausibly from tholins. The H & L article only discusses pure H2 water ice. Without speculating about how thick the layer of tholins might be, it would at least affect heating and evaporation.
Can’t be bothered with Avi Loeb’s blatherings at this point, other than perhaps taking bets on how long it will be before he shows up in the Journal of Cosmology.
A more interesting question is the reaction to they hydrogen theory from the “nitrogen iceberg” camp… Steve Desch doesn’t seem too impressed:
https://twitter.com/Deschscoveries/status/1638663242057945088
https://twitter.com/Deschscoveries/status/1638664184450936832
https://twitter.com/Deschscoveries/status/1638981451143344128
The N2 iceberg, imho, is the simplest explanation. We have evidence of a “planet” capable of producing N2 icebergs, Pluto, within the Solar System. The challenge that we have never before seen a N2 iceberg isn’t a significant challenge to the hypothesis. Science, especially astronomy, is constantly revealing new phenomenon. No one expected Pluto to look the way it does. There is something dysfunctional in using “the never before seen” challenge in the context of a phenomenon, ‘Oumuamua, that was never before seen.
The natural and artificial camps aren’t both dueling with wet noodles. One camp is; the artificial camp can shape its noodle however it pleases and can never be tested. The natural camp must prepare a five course pasta meal that everyone agrees is delicious. Loeb can invent any answer he chooses for why there is no decceleration provided by a solar sail, or why the mass is high enough to challenge the assumption of a solar sail. He can assign an untestable solution to solve any challenge. The two camps are not playing by the same rules. Despite the evidence that nature is filled mostly with just-so examples of natural phenomenon, the natural camp is criticized when relying on just-so explanations.
Peter Duesberg was well known for denying that AIDS was caused by the HIV virus. In that case it was a case of scientific denialism. He stated that he would be injected with HIV to prove his hypothesis by not getting AIDS but never carried out the experiment. With Loeb it seems to be a case of attempting to stretch very thin data by an implausible amount to provide evidence for alien visitations. It doesn’t seem worthwhile to me any more than Duesberg’s speculations did.
I may be dismissive of the alien hypothesis, but I’d say Loeb is nothing like Duesberg. He is not denying well-established science based on flimsy if any evidence, nor is he trying to convince people to lose their lives. To the contrary, here he legitimately spotted a bug in a paper, and the correction advances the state of understanding about this object – whose (no doubt natural) composition remains nonetheless highly uncertain!
Those are fair comments Mike. I still think Loeb goes too far with the available data but his criticisms of the recent manuscript seem reasonable to me. To be fair to Duesberg also, he didn’t try to convince anyone else to inject themselves with HIV. He said he would do it to himself but never did.
As I recall the history of HIV denialism was complex and dramatic. Duesberg touted the position that HIV was a harmless virus that infected people whose immune systems had already been destroyed by drugs, giving the overly hopeful an excuse to ignore public health measures. He also criticized antiretroviral drugs as toxic. Wikipedia gives him credit for contributing to the deaths of hundreds of thousands of people under Mbeki’s policies. I’m not convinced things were that clear-cut (read about South Africa 1999 in https://www.wired.com/story/opinion-the-world-loses-under-bill-gates-vaccine-colonialism/ ); to be brief I suspect he may have been pushed to unwarranted prominence as a pawn in a larger war.
The scientific back and forth on this issue is thrilling, providing as it does a glimpse into the messiness of scientific inquiry.
Is the subject a bit whimsical? Perhaps. It’s certainly fun.
Avi Loeb discusses the paper on Event Horizon, John Michael Godier’s podcast.