Many Stars Could Have Sent Us ‘Oumuamua

When astronomers detected the first known interstellar object, ‘Oumuamua, in 2017, it sparked a host of new studies trying to understand the origin and trajectory of the galactic sojourner.

‘Oumuamua’s unique properties – unlike anything orbiting our sun – had scientists pondering how such an object could have formed. Now, a pair of researchers, Xi-Ling Zheng and Ji-Lin Zhou, are using numerical simulations to test out possible solar system configurations that could result in ‘Oumuamua-like objects. Their findings show that solar systems with a single giant planet have the necessary orbital mechanics at work to create such an object – but that other explanations may still be required.

Zheng and Zhou published their findings in the Monthly Notices of the Royal Astronomical Society in February 2025.

They began their study by working backward from the known properties of ‘Oumuamua.

When it was visible to Earth’s telescopes for just a few months in 2017, it showed an intensely variable brightness, changing from bright to dim every four hours. Astronomers interpreted this variability as an elongated, cigar-shaped object tumbling through space.

Two other things made ‘Oumuamua unique. First, it appeared to have a dry, rocky surface, akin to the asteroids known in our solar system. But it also changed its orbit in a way that could not purely be explained by the laws of gravity – something else made it change direction.

Redirections like this are sometimes seen in icy comets. As they approach the Sun, off-gassing released from the heated ice acts like a thruster, changing the comet’s trajectory.

Somehow, ‘Oumuamua displayed a mix of both comet-like and asteroid-like properties.

One plausible explanation, proposed in 2020, is that ‘Oumuamua-like objects are formed by tidal fragmentation. That’s when a ‘volatile-rich’ parent body (like a large comet) passes too close to its star at high speeds, shattering it into long, thin shards. The heating process in these extreme interactions causes the formation of an elongated rocky shell, but preserves an interior of subsurface ice. This unique combination, not seen in our own solar system, would explain ‘Oumuamua’s orbital maneuvers despite its rocky composition.

It also explains why we don’t tend to see them in our solar system, because “ejected planetesimals experienced tidal fragmentation at more than twice the rate of surviving planetesimals (3.1% versus 1.4%),” the authors write. In other words, if the orbital forces are strong enough for tidal fragmentation to happen, it also means they’re strong enough to kick the object out of the system entirely.

Interstellar space may therefore be full of dagger-shaped shards of rock and ice (an exaggeration, but a fun quote for dinner parties nonetheless).

The simplest star system that could cause this type of tidal fragmentation are those home to white dwarfs. These are the extremely dense, dead cores of old exploded stars. A white dwarf, encircled by a belt of distant comet-like objects, similar to the Sun’s Oort cloud, could spawn ‘Oumuamua clones with regular frequency.

But the process is enhanced in systems that host Jupiter-sized planets.

The exception is ‘Hot Jupiters’ that orbit close to their star. These are less likely to interact with objects subject to tidal fragmentation.

But Jupiter-sized planets distant from their host star are very effective at producing ‘Oumuamua clones, especially if they have eccentric orbits. But even here, it’s not a perfect match for the origin of ‘Oumuamua, because these interactions tend to produce shards that are not as elongated, and at a rate lower than what is expected for ‘Oumuamua-type objects.

The authors conclude that the planetary systems most likely to have spawned ‘Oumuamua are those with many planets, which are more “efficient at producing interstellar objects,” the authors say, though they propose a few other possibilities too.

So while there is now a strong, plausible explanation for the process that birthed ‘Oumuamua, the type of solar system that produced it is still very much an open question.

Xi-Ling Zheng amd Ji-Lin Zhou, “Configuration of single giant planet systems generating ‘oumuamua-like interstellar asteroids.” Monthly Notices of the Royal Astronomical Society.

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