Also Neptune has wandered

The ice planet changed its orbit and brought "strangers" in the Kuiperg rtel

The ice planet Neptune was not always circling in its current orbit - and pushed other objects away. © NASA
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Exchange of places in the early solar system: The planet Neptune did not always circle in its current orbit. Instead, he emerged much further inside and only later went outside. He not only exchanged his place with Uranus, he also pushed many icy chunks into the Kuiper Belt, as observations now suggest. This explains why these chunks differ from the normal Kuiper belt objects, as the researchers report in the journal Nature Astronomy.

Today, the order of the planets in the outer solar system is clear: first comes Jupiter, then Saturn, Uranus and Neptune. But in the early days of our system, it probably looked quite different. Planet researchers assume that the gas giant Jupiter even twice traveled across the solar system - first to the inside, then back to the outside.

View into the Kuiper belt

But Jupiter is obviously not the only "wanderer" in the solar system, as Wesley Fraser of Queen's University Belfast and his colleagues have now discovered. For their study, researchers used two telescopes on Maunakea in Hawaii to study a population of unusual Kuiper belt objects.

Typically, the wide ring of icy objects beyond Neptune is populated by debris from the early days of planet formation. Most of these distant chunks appear slightly reddish upon observation in visible light and fly around one at a time. According to popular doctrine, they were created in the Kuiper Belt and are relics of the original cloud there.

Enigmatic double chunks

But Fraser and his colleagues discovered a whole population of unusual outliers: chunks that reflect the sunlight rather bluish and also mostly in pairs revolve around the sun. These two partners in these double objects orbit each other like the moon and the earth and are coupled together by their gravitational force, as the researchers explain. display

The migration of Neptune once also brought a pair of asteroid pairs like this one into the Kuiperg rtel. Gemini Observatory / AURA, Joy Pollard

The characteristics of these unusual double chunks speak against the fact that they are their individual conspecifics in the Kuiperg rtel. Instead, they must have their origin much further inward in the solar system, as planetary simulations suggest. According to these, these pairs originate from the region by 38 astronomical units and thus from an area just outside the Neptune orbit.

Exchange of places in the young solar system

But how did the double lumps ever go? And that, without the only slightly by gravity bound together pairs were separated by turbulence? In the opinion of Fraser and his colleagues, the answer could be the planet Neptune. For quite some time, astronomers suspect that the ice planet did not originate in its orbit today, but, like Jupiter, first migrated there.

According to this scenario, Neptune formed at a distance of about 20 astronomical units (AU) from the Sun approximately where Uranus circles today. Uranus, on the other hand, was still circling. Only about 650 million years after their formation, both planets began to migrate and exchange their places. The Neptune moved to its current orbit around 30 AU away from the sun.

Slow drift

And here come the mysterious double chunks in the Kuiperg rtel in the game: Fraser and his colleagues suspect that Neptune has pulled these icy chunks in his Au enwanderung. "We show that the double objects could have overcome such an outward shift by the early migration of Neptune, " the researchers said.

The prerequisite for this, however, was that the Neptune walk was very slow and quiet. Only then would the fragile gravity band between the respective partner chunks survive this shift. The new observations coupled with models of planetary motion not only explain where the mysteriously blue double chunks in the Kuiper Gorge originated, they also support the theory of an early migration of the planet Neptune.

"Our results have given us deeper insights into the early stages of planetary evolution, " says Fraser. "We now have good clues as to how and where the blue double objects were created." (Nature Astronomy, 2017; doi: 10.1038 / s41550-017-0088)

(Queen's University Belfast, 06.04.2017 - NPO)