Deep in the outer reaches of the solar system, an unusual object is moving against the flow of cosmic traffic, cutting across the Sun’s orbital plane at a remarkably steep angle. Scientists aren’t sure exactly how it got there; either it was tossed into its unique trajectory by Neptune or it’s an interstellar visitor from another star system.

The Rubin Observatory in Chile first spotted the object beyond the orbit of Neptune at a distance of approximately 3 billion miles (4.8 billion kilometers). While most planets, asteroids, and comets orbit the Sun in a relatively flat plane, this newly discovered object follows a retrograde path defined by a highly inclined orbit.

It’s not yet clear whether this object, temporarily designated R631, is a rocky body or a volatile-rich comet, or how it ended up in this backward trajectory around the Sun.

To understand why most planets and other objects orbit the Sun along roughly the same flat plane, we need to rewind to the birth of the solar system some 4.6 billion years ago.

It all began with a giant cloud of gas and dust that collapsed under its own gravity, eventually flattening into a thin, rotating disk around the young Sun. As dust grains within this disk collided and clumped together, they gradually grew into larger bodies, eventually giving rise to the planets and other solar system objects. Having emerged from the same rotating disk, most of these bodies inherited its relatively flat orbital arrangement.

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