When the object now known as 1I/ʻOumuamua streaked through the inner Solar System in 2017, it instantly rewrote the playbook on what small bodies in space can look like. It was the first confirmed visitor from another star system, and its odd shape and motion defied every familiar category of comet or asteroid. Today, a growing body of work argues that this interstellar traveler may be a frozen shard from the surface of a Pluto-like world, chipped off in a distant planetary system and set adrift for hundreds of millions of years before its brief encounter with the Sun.
I see that idea as more than a clever origin story. If ʻOumuamua really is a fragment of an “exo‑Pluto,” it hints that icy dwarf planets with volatile rich crusts are common in the galaxy, and that violent collisions can scatter their debris across interstellar space. It also offers a natural explanation for the object’s strange shape, brightness and subtle acceleration, without invoking exotic physics or alien engineering.
The first interstellar visitor that refused to behave
Astronomers first spotted the object that would be named Oumuamua racing through the inner Solar System on a sharply inclined, hyperbolic path, making it clear that it came from outside the Sun’s gravitational family. When 1I/Oumuamua was tracked more closely, its speed and trajectory showed that it was not bound to the Sun at all, confirming it as the first known interstellar object to pass through our neighborhood. Observers quickly realized that its elongated, tumbling shape and rapid brightness variations did not match any familiar comet or asteroid population.
Early analyses suggested that the visitor was either cigar shaped or, as later modeling favored, more like a flattened pancake, with a highly reflective surface that made it brighter than typical rocky bodies of similar size. One study described the interstellar object as a pancake shaped chunk of a Pluto-like planet, highlighting how its thin profile and sheen could be consistent with a volatile rich crust similar to Pluto. That same work emphasized that this was the first known interstellar object, with a second such visitor, 2I/Borisov, only discovered later, underscoring how unprecedented ʻOumuamua’s properties were.
From alien probe speculation to exo‑Pluto shard
Because the object showed a small but measurable non gravitational acceleration as it moved away from the Sun, without the visible gas and dust tail of a normal comet, some researchers and commentators speculated that Oumuamua might be artificial. It was even floated as a possible alien probe, an idea that captured the public imagination precisely because the data were so limited and the object was already receding into the dark. Yet as more teams revisited the observations, a different picture emerged, one that treated the acceleration as a clue to composition rather than a sign of technology.
New modeling work argued that the most straightforward explanation was that Oumuamua is a chip knocked off an icy, Pluto-like exoplanet, with its surface dominated by volatile ices that can sublimate under solar heating. In this view, the object’s non gravitational push comes from escaping material that is too transparent or diffuse to form a classic comet tail, but still strong enough to alter its path. One analysis framed ʻOumuamua as a fragment of nitrogen ice from an exo-Pluto, noting that solid nitrogen ice is seen on the surface of Pluto and could plausibly make up a cometlike object in another system. A related study described the interstellar visitor as a cookie shaped planet shard, reinforcing the idea that we were seeing a sliver of a once larger, differentiated world rather than a monolithic rock.
Nitrogen ice and the case for an “exo‑Pluto”
The nitrogen ice hypothesis tries to solve several puzzles at once: the object’s brightness, its thin, flattened shape and its gentle acceleration away from the Sun. If Oumuamua is mostly nitrogen ice, similar to the 98% N2 ice that dominates parts of Pluto’s surface, then solar heating could erode it efficiently, shaving off layers and gradually sculpting a flattened shard. Advocates of this model argue that no extraterrestrial technologies are needed, only the physics of volatile rich ices common in the outer Solar System and, by extension, in other planetary systems.
In technical work presented to the scientific community, researchers relaxed some of the initial assumptions about the object’s shape and outgassing, then showed that matching the observed trajectory required adding a non gravitational force driven by sublimation of nitrogen ice. That analysis treated Oumuamua as a fragment of N2 ice from an exo-Pluto, with its unusual motion emerging naturally once the volatile composition was included in the models, as summarized in the abstract labeled Further. A broader press briefing on this work described an illustration of a plausible history for Oumuamua that begins in its parent system around 0.4 billion years ago, with erosion by cosmic rays and stellar radiation gradually whittling it into the thin, elongated shape we inferred from its changing brightness.
Reconstructing a 0.4 billion year journey
To trace that journey, scientists start with a Pluto-like planet orbiting a distant star, its surface coated in nitrogen ice and other volatiles. A collision with another body could blast chunks of its outer layers into space, some of them escaping the system entirely. Over roughly 0.4 billion years, according to one Illustration of this scenario, those fragments would be bombarded by cosmic rays and starlight, steadily eroding their surfaces and altering their shapes. By the time one such shard wandered into our Solar System, it would be a thin, reflective sliver, already pre sculpted by eons of exposure.
As it approached the Sun, the remaining nitrogen ice would begin to sublimate, providing a gentle rocket effect that nudged its trajectory without producing a bright, dusty tail. Using its shininess, size and shape, and the fact that it was propelled by escaping substances that did not produce a visible tail, planetary scientist Steven R. Desch and colleagues, including Alan P. Using Jackso, argued that the object fits neatly into this exo-Pluto fragment category. In their view, Oumuamua is not a one off oddity but the first detected member of a broader class of interstellar debris, with many more such shards likely drifting between the stars.
Debate, new data and what comes next
Not everyone is convinced that nitrogen ice is the full story. A later critique argued that Oumuamua was not a nitrogen iceberg, pointing out that the amount of nitrogen ice required to populate interstellar space with enough such fragments might be difficult to reconcile with what we know about exo-Plutos. That work noted that as the flat, wonky shaped object passed the Sun, tumbling end over end, it accelerated at a pace that could not easily be explained if it were simply a chunk of nitrogen that had split away from exo-Plutos, and suggested that alternative compositions or mechanisms might be needed, as summarized in the analysis introduced with the phrase As the. Other teams have explored hydrogen ice and mixed volatile models, with one overview noting that a significant amount of Hydrogen ice inside Oumuamua would point to an origin in extremely cold regions of space, though that idea faces its own survival and production challenges.
Despite the disagreements, the Pluto-like shard hypothesis has continued to gain traction, especially as more researchers frame Oumuamua as an “exo-Pluto,” a completely new class of object. At a recent gathering, scientists emphasized that when 1I/Oumuamua was first detected, it surprised everyone by coming from outside the Solar System and by behaving unlike any known comet. Coverage of that work described Oumuamua as an exo-Pluto, tying it directly to the nitrogen ice fragment scenario and reinforcing the idea that dwarf planets with Pluto-like surfaces may be common in other systems. A separate report noted that Four years after astronomers first detected Four Oumuamua, new research strengthened the case that it is the shattered remnant of a Pluto-like object, while a recent video briefing highlighted how Scientists studying Scientists Oumuamua now describe it as a chunk of a Pluto-like planet.
More from Morning Overview