I’m not going to lie to you: I was pinning a lot of my alien-related hopes on ‘Oumuamua. I had put basically all of my UFO-shaped eggs into that one perplexing interstellar object, and now one wet blanket–esque team of scientists has published a paper with the sole intention (note: possibly not true) of shitting on my dreams.

If, unlike me, you haven’t been keeping your nose firmly pressed against the glass of your laptop screen, impatiently hammering the refresh button on a Google News search for “‘Oumuamua“, here is a quick breakdown: Back in 2017, for the first time ever, we spotted and catalogued an interstellar object — something that had entered into our solar system from outside of it. Further observation suggested that the object was weirdly elongated, spinning in an odd fashion, and (here’s the spicy bit) accelerating in a way that we couldn’t explain.

The data suggested that ‘Oumuamua was speeding up faster than it should be on gravity alone. This is not unusual by itself, but there was crucially also the absence of any evidence of outgassing. Outgassing is when comets eject mass as they get warmed by the sun, which can cause the comet to increase in speed. Adding to that weirdness, modelling indicated that outgassing would have caused ‘Oumuamua’s spin to rapidly change, which would have caused it to break into pieces. So, if that wasn’t what was making ‘Oumuamua speed up by itself, what was?

If you asked Abraham Loeb, the chair of the astronomy department at Harvard, he would have told you is that the answer is quite possibly ‘aliens’:

The only hypothesis I could think of is a push from solar radiation pressure. For that to work, the object would have to be very thin, less than a millimeter thick, in other words a type of pancake. In addition, the Spitzer Space Telescope found no evidence of heat emission from the object, and that means that it is at least 10 times more reflective than a typical comet or asteroid. What we have, then, is a thin, flat, shiny object. So I arrived at the idea of a solar sail: A solar sail is a spaceship that uses the sun for propulsion. Instead of using fuel, it is propelled ahead by reflecting light. In fact, it’s a technology that our civilization is developing at this very time.

Unfortunately, due to the fact that ‘Oumuamua is now hightailing it towards the edge of the solar system at around 100,000km/h, we will not have an opportunity to closely study it or, say, catch up to it and tap on one of its alien portholes. This leaves the questions of its nature and origin either frustratingly mysterious or hidden somewhere in the data already recorded.

Much to my dismay, a multinational team of astronomers headed up by Matthew Knight from the University of Maryland and Alan Fitzsimmons from Queen’s University Belfast have published a paper on the matter where they looked at the data and concluded that there’s no reason to think aliens played any part in it.

Published today, the paper The natural history of ‘Oumuamua provides several natural explanations for the behaviour of the interstellar object and even specifically challenges some of Loeb’s claims as to how it could be a solar sail.

While the researchers confirmed there was no visible evidence of outgassing, they did suggest that the loss of mass could have been from water beneath the object’s surface escaping later in the process than regular outgassing:

Thermal models show that ices may exist within just ~30 cm of the surface without being released during ‘Oumuamua’s perihelion passage. A natural consequence would be a thermal lag in which outgassing begins much later. Such a scenario would decrease the total amount of volatile material needed to explain the observed non-gravitational acceleration and shorten the timescale over which torques were at work. One thermal model was shown to be consistent with the observed non-gravitational acceleration by assuming outgassing from water in combination with another volatile species.

This late outgassing means that the object would be doing so under less gravitational pull from the sun, thus less mass would need to be ejected to accelerate at the observed rate.

They also rejected the suggestion that the supposed rarity of interstellar objects meant that it passing right through our solar system was a bit suspicious:

While provocative, this argument is baseless. First, ‘Oumuamua’s trajectory is consistent with predictions for detectable inactive interstellar objects. Second, the measured number density cannot be claimed to be at odds with expectations because of our ignorance of the size distribution of interstellar objects. Thus, we find no compelling evidence to favour an alien explanation for ‘Oumuamua.

This honestly feels like a personal affront.

The researchers quite rudely put a pin in the suggestion that Spitzer Space Telescope observations could support a solar sail:

The claim73 that ‘Oumuamua must be at least ten times ‘shinier’ than all Solar System asteroids to make the Spitzer Space Telescope data consistent with the ground-based observations is incorrect. The Spitzer observations are consistent with geometric albedos 0.01 ≤ pv ≤ 0.5 (ref. 3), with a most likely albedo of pv ~ 0.1. Comets have geometric albedos of pv = 0.02–0.07, carbonaceous and silicate asteroids have pv = 0.05–0.21, and the most reflective asteroids have pv ~ 0.5 (refs. 75,76). Thus ‘Oumuamua’s measured reflectivity of about 0.1 is entirely consistent with normal Solar System small bodies.

I’m no scientist but I believe this is basically the astronomy paper equivalent of doing a suplex on Loeb and his theory.

While this may put a dampener on the alien theory, there are still unanswered questions about ‘Oumuamua, namely: how it came to be shaped so weird, why it’s spinning the way it is, and where it came from.

I want to believe.

Image: ESO/M. Kornmesser