Is there a young ‘Earth’ forming in between colliding ‘Plutos’?

Is there a young ‘Earth’ forming in between colliding ‘Plutos’?

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Did you ever wonder where the Earth came from? A few billion years ago, it slowly grew from dust in the newborn solar system. Dust particles stuck together to form larger grains. The grains grew into boulders, and then into small objects known as planetesimals. Eventually, the rocky planetesimals collided to form the inner planets, including Earth.

Astronomers always thought that small planets like Earth could only form close to their parent stars, where enough dust is available. But ALMA has now found possible signs of a newborn Earth-like planet at an incredibly large distance from its star: more than ten billion kilometres.

ALMA was able to map millimetre-sized grains in the disk of dust surrounding HD 107146 – a ‘baby star’ only some 100 million years old. Surprisingly, most of the grains turn out to be in the outer parts of the disk. In the inner parts, the grains may already have coalesced into full-fledged planets.


But why are there so many dust grains in the outer parts of the disk? Astronomers think it’s because there are so many small objects like Pluto out there. They are between a few hundred and two thousand kilometres across. These ‘Plutos’ are pulverized when they collide with each other. That’s where the dust grains come from.

The discovery of a thick belt of dust grains so far away from a star is interesting enough. But the ALMA observations revealed something else, too. There seems to be a broad, ring-like gap in the disk: at a certain distance from the central star, the number of dust grains is much lower than average.

This may be due to the presence of a planet as large as Earth. The planet’s gravity would sweep up most of the grains in its orbit. It would be the first time that an Earth-like planet is discovered so far away from its parent star.

Future observations, whit the ALMA antennas spread out over a larger area, will yield sharper images of HD 107146’s dusty disk. Hopefully, astronomers will then be able to learn more about the origin of the gap.

HD 107146 is a very young star. It formed only some 100 million years ago. For comparion: our own Sun is 46 times older than that. But apart from its young age, HD 107146 is more or less comparable to the Sun. It is located in the constellation Coma Berenices (Berenice’s Hair), at a distance of some 90 light years.

The ALMA observations of HD 107146 were carried out by a group of American astronomers, led by Luca Ricci, who was then at the California Institute of Technology in Pasadena. Luca has since moved to the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. The team published their findings in The Astrophysical Journal.