The ‘Sandwich’ discovery offers a new explanation for planet formation

July 05, 2023

(Nanowerk News) Scientists have made a new discovery about how small planets can form. Researchers at the University of Warwick investigated a planet’s ‘birth environment’ – the area of ​​gas and dust that revolves around a central star – known as the protoplanetary disk.

They discovered a new method of planet formation in this region, which had not been described in previous studies. The work has been submitted to the journal Monthly Notices of the Royal Astronomical Society and is on display at the National Astronomy Meeting, which begins today, Monday 3 July. The team showed how two large planets in a protoplanetary disk could potentially give rise to a smaller planet between them – what they called “squipped planet formation”.

The reason is because the two large original planets restrict the inward flow of dust. This means that the amount of dust that collects between them is less than if there were no outer planets. If the dust does eventually coalesce to form a planet, then the central planet will likely be smaller than the outer two – like the filling in a sandwich. Artistic rendering of how a minor planet could form ‘squeezed’ between two larger planets. (Image: Mark A. Garlick, University of Warwick)

While more research is needed in the field, this theory could provide a possible explanation for the formation of minor planets; like Mars and Uranus, each of which is surrounded by a larger planet.

Associate Professor and Dorothy Hodgkin Fellow, Farzana Meru, from the Department of Physics at the University of Warwick, said: “In the last decade, observations have revealed that there are rings and fissures in the protoplanetary disk. The gap is where we would expect a planet to be, and we know from working theory that the planet caused a ring of dust to form just outside it. What exactly is happening in the rings raises important questions for astronomers around the world.

“In our research, we propose rings as sites of planet formation; in particular, that there are squashed planets currently forming in the rings. This is in sharp contrast to the conventional view of planet formation, in which we would normally expect planets to form sequentially from the inner to outer disks and become progressively more massive the farther out. What’s also really interesting is that there are examples we’ve found from exoplanet observations that really demonstrate this wedged planetary architecture — where the central planet is less massive than its neighbors; it’s a reasonable proportion of the system too.

“The planet formation field has undergone a revolution recently. High-resolution images of the planet-forming disks have emerged in the last ten years since new advanced telescopes (Atacama Large Millimeter/submillimeter Array) began observing the night sky. These images give us clues about how planets form and evolve; It’s been a pleasure to be at the forefront of this research.”

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