Neptune's 'Smooth And Calm' Migration Swept Blue Binary Planetoids To Solar System's Edges

The Kuiper Belt is a cold, dark region of space that lies beyond the orbit of Neptune. This region is populated with trillions of icy objects that are remnants of the formative years of the solar system.

In a new study, a team of astronomers has described how the gas giant Neptune played a key role in shaping a part of this region. The study, published Tuesday in the journal Nature Astronomy, focussed on a class of “oddball” blue binary planetoids known as Cold Classical Kuiper Belt Objects (CCKBO)

“The red CCKBOs are thought to have formed at the location in the outer solar system where they currently reside. The blue binaries, on the other hand, are interlopers from closer in hiding out in the Kuiper belt today,” study co-author Megan Schwamb, an astronomer at the Gemini Observatory, said in a statement released Tuesday.

Although objects in the Kuiper Belt exhibit a range of colors, from red to blue to white, the so-called cold classical objects are overwhelmingly red — a possible sign of the presence of organic materials. The blue-colored binary CCKBOs, on the other hand, are an exception, as they don’t share the color that distinguishes most other CCKBO’s surfaces.

The study, based on observations carried out using the Gemini-North and Canada-France-Hawaii telescopes, suggests that blue binaries actually formed in a region much closer to the Sun and were then shepherded by Neptune’s gravitational nudges to their current orbits in the distant Kuiper Belt billions of years ago. If this is true, it would mean that Neptune’s journey to the edges of the solar system was “gentler and kinder” than previously thought.

“There has been some evidence around how Neptune moved outwards to 30 AU [astronomical unit]. Our hypothesis about how these blue binaries came to be where they are requires that Neptune’s migration was largely a smooth and calm movement,” study co-author Wesley Fraser, from Queen's University Belfast, said in a separate statement.

The observations not only significantly advance our understanding of the formative years of the solar system and planetary growth, but also shed light on where the mysterious blue binary planetoids originated.