No, I don’t think there’s any reason to think it is, but there’s lots of chatter on Twitter that suggest astronomers think it could be:
— David W. Hogg (@davidwhogg) November 21, 2017
So what’s going on?
For the first time, astronomers think they have found an interstellar asteroid. It is clearly on an escape trajectory, and everything about its path is consistent with a free-floating asteroid that was ejected from another star system and is now happening to buzz by the Sun:
There are several things that have astronomers talking “spaceship”:
- Its discovery closely tracks the opening chapter of the book Rendezvous with Rama, by Arthur C. Clarke, about the discovery of an interstellar spaceship on a similar trajectory to ‘Oumuamua.
- We were expecting the first discovered interstellar rocks (we know they must be out there) to be comets, since our own Solar System’s Oort cloud (populated by nearly-ejected Solar System detritus) is mostly comets. The fact that it is not a comet has people scratching their heads.
- One of the recent measurements of its shape finds it to have a 10:1 axis ratio: this is not typical of asteroids, but is not uncommon for ships in science fiction (the 2001 monolith was 1:4:9)
- One of the recent measurements of its color has it very red, similar to metallic asteroids
In many ways, this discovery tracks the excitement around Tabby’s Star: a prediction of how we might discover alien life was made (Clarke for ‘Oumuamua, Luc Arnold for Tabby’s Star); and later an anomalous object was found roughly tracking that prediction but confounding natural explanation.
I’m glad that astronomers are talking about this in a SETI context (and this is SETI), but my personal prior on this is that there is not much reason to get excited about the SETI angle.
That’s because there are several important differences between ‘Oumuamua and Tabby’s Star:
- The data on Tabby’s Star from Kepler are exquisite. What’s more, only after being convinced that there was no chance of instrumental error did it really get interesting. The data on ‘Oumuamua is thin: different groups are getting different sizes, rotation periods, axial ratios, and colors for the object, meaning that it hasn’t been well measured yet. For instance:
Interestingly, it looks to me like the (g-r) color derived for ‘Oumuamua from Meech et al. (in press) are inconsistent with that of Banister et al (submitted) at the 3-sigma level. Full disclosure, I’m a co-author on the Bannister paper.
— Meg Schwamb (@megschwamb) November 20, 2017
- The various values people get for the axial ratio vary from the hard-to-understand 10:1 to the more ordinary 3:1. In other words, it’s not at all clear that this characteristic of ‘Oumuamua is actually all that anomalous—the 10:1 measurement could be in error.
- Tabby and her team put 2 years of hard work into understanding that star. Only after all of that work was the “hypothesis of last resort” something worth publishing. ‘Oumuamua was discovered a month ago.
- Tabby’s team’s ruling out of most natural explanations built on decades of stellar astrophysics and understanding of stars and their environments. ‘Oumuamua is the first interstellar asteroid we’ve seen, so we have very little to go on.
…or of things that have *not* been subject to 4.5 billion years of Solar System processes. How long would #Oumuamua have lasted in that form in the asteroid belt? I don’t know.
— Jason Wright (@Astro_Wright) November 22, 2017
So I’ll need to see a lot more data and hard, critical analysis of the anomalies in ‘Oumuamua before I get interested in the SETI angle at the level I am for Tabby’s Star.
That said, I’m glad that astronomers are, on the informal forum of Twitter anyway, having a SETI discussion about the prospect of discovering interstellar probes passing through the Solar System. It’s a neat topic, and once worth thinking about. I hope ‘Oumuamua inspires more real work on it in the peer-reviewed literature, including concrete suggestions of what to look for when future interstellar objects are discovered passing through.
[Update: please see this Twitter thread by Michele Bannister:
1. We do have local examples: the Oort cloud is the <5% capture efficiency of the ejecta, & contains both comets & asteroids ("Manx comets").
2. We have multi-Gyr outside-heliopause-processed (but bigger) objects. `Oumuamua does not share their "ultra-red" colours.
— Michele Bannister (@astrokiwi) November 22, 2017
This article (in German, but Google Translate) by Daniel Fischer:
and the comment by Darin Ragazzine below for more-informed takes on this whole issue. Where they contradict me, you should trust them, because they are actual planetary scientists that work in this field.