The debate continues: ‘Oumuamua could be remnant of Pluto-like planet

The mysterious pancake-shaped object dubbed ‘Oumuamua (Hawaiian for “messenger from afar arriving first”) generated considerable controversy earlier this year with the publication of Harvard astronomer Avi Loeb’s bestselling new book arguing that it could be a piece of alien technology. Now two astrophysicists at Arizona State University (ASU) are counterarguing that the secret to at least one aspect of the object’s unusual properties lies in solid nitrogen ice. They described their findings in two new papers published in the Journal of Geophysical Research: Planets.

As we reported previously, in late 2017, our Solar System received its very first known interstellar visitor: a bizarre cigar-shaped object hurtling past at 44 kilometers per second. Scientists have been puzzling over the origin and unusual characteristics of ‘Oumuamua ever since. It was first discovered by the University of Hawaii’s Pan-STARRS1 telescope, part of NASA’s Near-Earth Object Observations program to track asteroids and comets that come into Earth’s vicinity. Other telescopes around the world soon kicked into action, measuring the object’s various characteristics.

Because it had a hyperbolic, or escape, orbit around the Sun, ‘Oumuamua is unlikely to pass our way again. So astronomers only had a brief window of time to gather as much data as they could about the object before it went on its merry way. For starters, ‘Oumuamua was accelerating away from our Sun much faster than could be explained by gravity alone—i.e., via a “rocket effect” that is common in comets, caused by sunlight vaporizing the ice such bodies are made of. While its odd orbit initially had it categorized as a comet, imaging didn’t show any indication of gas and dust being released, as is typical when a comet approaches the Sun. Its elongated, cigar-like shape, combined with its relatively rapid rotation, led to an early suggestion that it could also be an asteroid.