Anomalous objects are a problem — we need more than one to figure them out. One ‘hot Jupiter’ could have been an extreme anomaly, but we went on to find enough of them to realize this was a kind of planet that had a place in our catalog. Or think of those two Kuiper Belt objects that New Horizons imaged, as discussed in yesterday’s post. Soon we’ll have much closer imagery of MU69, but it will take more encounters — and more spacecraft — to begin to fathom the full range of objects that make up the Kuiper Belt. Ultimately, we’d like to see enough KBOs up close to start drawing statistically valid conclusions about the entire population.
So where does the intriguing ‘Oumuamua fit into all this? It was the first interstellar asteroid we’ve been able to look at, even if the encounter was fleeting. A friend asked me, having learned of the Breakthrough Listen SETI monitoring of the object, whether it wasn’t absurd to imagine it could be a craft from another civilization. I could only say that the idea was highly unlikely, but given how little time we had and how rare the object was, how could we not have listened? I favor throwing whatever resources we have at an opportunity this unusual.
And time was short, as Joshua Sokol recently noted in Scientific American. We found ‘Oumuamua in late October of last year, but getting a probe to it on the best possible trajectory would have demanded a launch the previous July. I see that Greg Laughlin (UC-Santa Cruz), working with Yale doctoral student Darryl Seligman, has been exploring how we might drive an impactor into a future interstellar visitor, allowing the kind of analysis we did with the Deep Impact mission. I’ll have more on the idea as the paper wends its way through peer review.
Image: This animation shows the path of ‘Oumuamua, which passed through our inner solar system in September and October 2017. From analysis of its motion, scientists calculate that it probably originated from outside of our Solar System. Credit: NASA/JPL-Caltech.
We appear to be getting into the era of comparative interstellar object studies. One, two, many ‘Oumuamuas, not to mention their cousins, who may not just pass through but stick around. Harvard’s Avi Loeb, working with Manasvi Lingam (Harvard-Smithsonian Center for Astrophysics), offers a paper on ‘Oumuamua that’s now available on the arXiv server. Here we get a sense of the broader population of interstellar objects, not all of which may have departed.
The authors have approached the question by asking how likely it is for interstellar objects to be captured in our Solar System, performing the same kind of analysis for the Alpha Centauri system. The scientists believe several thousand captured interstellar objects may be within the Solar System at any given time, with the largest of these reaching tens of kilometers in size.
‘Oumuamua came and went quickly, but a long-lingering population offers us ample grounds for investigation. Likening the effects of the Sun and Jupiter to a fishing net, the authors peg the number of interstellar objects currently within the system at ~ 6 x 103, pointing out that they offer us the potential to study exoplanetary debris without leaving our own system.
But how to determine whether an object now bound to our Solar System really is interstellar in origin? The answer may lie in the chemical constitution of water vapor found associated with the object. The oxygen isotope ratios may hold the key, as the paper explains:
…if the oxygen isotope ratios are markedly different from the values commonly observed in the Solar system, it may suggest that the object is interstellar in nature; more specifically, the ratio of 17O/18O is distinctly lower for the Solar system compared to the Galactic value (Nittler & Gaidos 2012), and hence a higher value of this ratio may be suggestive of interstellar origin.
To make this work, we could analyze these isotopes through high-resolution spectroscopy, working in the optical, infrared and submillimeter ranges of water vapor in cometary tails, just as the Herschel observatory was able to measure the isotope ratio of comet C/2009 P1 in the Oort cloud. A flyby and perhaps even a sample return mission could not be ruled out either, with the interesting implication that a technology like Breakthrough Starshot’s could be used to explore much closer targets than Proxima Centauri with short mission times.
But if thousands of interstellar objects are within our Solar System now, what implications does this offer for the emergence of life? The paper notes that some 400 interstellar objects with a radius in the 0.1 kilometer range could have struck the Earth prior to abiogenesis, and about 10 could have been kilometer-sized. The possibility of interstellar panspermia is evident. The paper continues:
If a km-sized interstellar object were to strike the Earth, we suggested that it would result in pronounced local changes, although the global effects may be transient. Habitable planets could have been seeded by means of panspermia through two different channels: (i) direct impact of interstellar objects, and (ii) temporary capture of the interstellar object followed by interplanetary panspermia. There are multiple uncertainties involved in all panspermia models, as the probability of alien microbes surviving ejection, transit and reentry remains poorly constrained despite recent advancements.
It’s interesting to note on this score that while the Solar System might have snared objects up to tens of kilometers in size, the Alpha Centauri system could capture objects up to Earth size, making for the possibility of a life-bearing world being acquired in its entirety.
‘Oumuamua work continues in a letter from Carlos de la Fuente Marcos (Complutense University of Madrid) that analyzes the orbits of 339 known hyperbolic objects and models their histories, finding eight possible interstellar objects within past astronomical observations. Unlike Loeb and Lingam’s population of captured objects, these visitors followed the ‘Oumuamua model, making a single brief appearance, but they offer the possibility that our archives contain further examples of such wanderers. The onset of observations with the Large Synoptic Survey Telescope in the early 2020s may help us further constrain the population of unbound objects.
The paper is Lingam & Loeb, “Implications of Captured Interstellar Objects for Panspermia and Extraterrestrial Life” (preprint). The de la Fuente Marcos paper is “Where the Solar system meets the solar neighbourhood: patterns in the distribution of radiants of observed hyperbolic minor bodies,” Monthly Notices of the Royal Astronomical Society 20 February 2018 (abstract).