It’s not aliens, but it could be a slimmed-down piece of an alien Pluto.
That’s the claim laid out in a pair of studies about the mysterious interstellar object known as ’Oumuamua, which passed through our solar system in 2017.
The studies, published in the AGU Journal of Geophysical Research: Planets, suggest that the flattened chunk of cosmic material consists primarily of solid nitrogen ice, much like the stuff on Pluto’s surface.
The debate over ’Oumuamua — whose name is derived from the Hawaiian phrase for “messenger from afar” — is still raging years after it zipped around the sun and headed back into the celestial darkness. Based on its trajectory, astronomers were certain it came from far beyond the solar system. But was it an asteroid? A comet? Could it even have been an alien spaceship?
Harvard astronomer Avi Loeb favored the alien hypothesis, due to ’Oumuamua’s weird shape and unusually fast getaway. He doubled down on the idea in “Extraterrestrial,” a book published in January. But the authors of the newly published studies, Arizona State University’s Steven Desch and Alan Jackson, say there’s no need to invoke aliens.
“Everybody is interested in aliens, and it was inevitable that this first object outside the solar system would make people think of aliens,” Desch said in a news release. “But it’s important in science not to jump to conclusions. It took two or three years to figure out a natural explanation — a chunk of nitrogen ice — that matches everything we know about ’Oumuamua. That’s not that long in science, and far too soon to say we had exhausted all natural explanations.”
In their research papers, Desch and Jackson propose that a cosmic impact in a faraway planetary system knocked off a piece of a Pluto-type world about half a billion years ago and sent it hurtling out into interstellar space. If the fragment consisted of frozen nitrogen, that would explain how it took on its unusual shape.
“As the outer layers of nitrogen ice evaporated, the shape of the body would have become progressively more flattened, just like a bar of soap does as the outer layers get rubbed off through use,” Jackson said.
That kind of composition could also explain why ’Oumuamua picked up more speed than expected as it left the solar system. Sunlight would have warmed up the object, causing ice to turn to gas. The pressure of the gas could have acted like a rocket thruster, pushing ’Oumuamua outward. Desch and Jackson determined that nitrogen ice could provide the right amount of push to match the observed trajectory.
“That was an exciting moment for us,” Desch said. “We realized that a chunk of ice would be much more reflective than people were assuming, which meant it could be smaller. The same rocket effect would then give ’Oumuamua a bigger push, bigger than comets usually experience.”
It’s not possible to confirm their hypothesis with ’Oumuamua, which is already too far out for detailed study. But Desch and Jackson say future telescopes, such as the one being built at the Vera Rubin Observatory in Chile, could survey the skies for more interstellar objects coming through. Other researchers recently estimated that, on average, seven such objects pass through the inner solar system annually.
“It’s hoped that in a decade or so we can acquire statistics on what sorts of objects pass through the solar system, and if nitrogen ice chunks are rare or as common as we’ve calculated,” Jackson said. “Either way, we should be able to learn a lot about other solar systems, and whether they underwent the same sorts of collisional histories that ours did.”
Yet another line of research, laid out today at the Lunar and Planetary Science Conference, suggests that alien Plutos — and other icy worlds that might harbor hidden oceans — could be prime territory for extraterrestrial life forms.
Alan Stern, a planetary scientist at the Southwest Research Institute who’s also principal investigator for NASA’s New Horizons mission to Pluto and the Kuiper Belt, argued that alien organisms living in ice-covered oceans might enjoy advantages over creatures living on the surfaces of planets. That’s because such organisms would be sheltered from asteroid and cosmic impacts, stellar flares and supernova blasts.
“Interior water ocean worlds are better suited to provide many kinds of environmental stability, and are less likely to suffer threats to life from their own atmosphere, their star, their solar system, and the galaxy, than are worlds like Earth, which have their oceans on the outside,” Stern said in a news release.
If such organisms are locked beneath a layer of ice, that could also answer the question posed by Fermi’s Paradox: Assuming that life is common in the universe, why haven’t we already run across it? “The same protective layer of ice and rock that creates stable environments for life also sequesters that life from easy detection,” Stern said.
Stern’s hypothesis about interior water ocean worlds, or IWOWs, could be put to the test in the decades ahead. Hidden oceans are thought to exist on several moons of Jupiter and Saturn — and NASA is already planning to send robotic probes to two of them, Europa and Titan.