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Meet our solar system’s 1st-known permanent immigrant

Mysterious asteroid 2015 BZ509 – currently nestling in Jupiter’s orbit – became less mysterious once astronomers realized it’s an immigrant, captured from another solar system.

Images of 2015 BZ509 obtained at the Large Binocular Telescope Observatory (LBTO) that established its retrograde co-orbital nature. The bright stars and the asteroid (circled in yellow) appear black and the sky white in this negative image. Image via C. Veillet/Large Binocular Telescope Observatory/RAS.

A new study has discovered the first known permanent immigrant to our solar system. The asteroid, currently nestling in Jupiter’s orbit, is the first known asteroid to have been captured from another star system. The new work is published in the peer-reviewed Monthly Notices of the Royal Astronomical Society: Letters.

The object known as ‘Oumuamua was the last interstellar interloper to hit the headlines in 2017. However, it was just a tourist passing through, whereas this former exo-asteroid – given the catchy name (514107) 2015 BZ509 – is a long-term resident.

All of the planets in our solar system, and the vast majority of other objects as well, travel around the Sun in the same direction. However, 2015 BZ509 is different – it moves in the opposite direction in what is known as a “retrograde” orbit. Fathi Namouni, lead author of the study, said:

How the asteroid came to move in this way while sharing Jupiter’s orbit has until now been a mystery. If 2015 BZ509 were a native of our system, it should have had the same original direction as all of the other planets and asteroids, inherited from the cloud of gas and dust that formed them.

However, the team ran simulations to trace the location of 2015 BZ509 right back to the birth of our solar system, 4.5 billion years ago when the era of planet formation ended. These show that 2015 BZ509 has always moved in this way, and so could not have been there originally and must have been captured from another system. Helena Morais, the other member of the team, commented:

Asteroid immigration from other star systems occurs because the sun initially formed in a tightly-packed star cluster, where every star had its own system of planets and asteroids.

The close proximity of the stars, aided by the gravitational forces of the planets, help these systems attract, remove, and capture asteroids from one another.

The discovery of the first-known permanent asteroid immigrant in the solar system has important implications for the open problems of planet formation, solar system evolution, and possibly the origin of life itself, these astronomers said.

Understanding exactly when and how 2015 BZ509 settled in the solar system provides clues about the sun’s original star nursery, and about the potential enrichment of our early environment with components necessary for the appearance of life on Earth.

Image of stellar nursery NGC 604 (NASA/HST), where star systems are closely packed and asteroid exchange is thought to be possible. Asteroid (514107) 2015 BZ509 emigrated from its parent star and settled around the sun in a similar environment. Image via NASA/Hubble Heritage Team/RAS.

Bottom line: Mysterious asteroid 2015 BZ509 – currently nestling in Jupiter’s orbit – became less mysterious once astronomers realized it’s an immigrant, captured from another solar system.

Source: “An Interstellar Origin for Jupiter’s Retrograde Co-Orbital Asteroid,” F. Namouni & H. Morais, 2018, to be published in Monthly Notices of the Royal Astronomical Society: Letters
[https://doi.org/10.1093/mnrasl/sly057 (after the embargo expires)].

Via RAS

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