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Big planets get a head start in pancake-thin




ALMA: Tablet Oph163131

image: Oph163131 disk images as seen by ALMA (left) and HST (right). The millimeter-sized particle boundaries in the disk observed by ALMA are shown in white. They are concentrated in a much narrower layer of fine dust (micron size) observed by the Hubble Space Telescope.
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Credit: ALMA (ESO / NAOJ / NRAO) / Hubble / NASA / ESA / M. Villenave

A study announced this week at the Europlanet Science Conference (EPSC) 2022 in Granada, Spain, shows that very thin planet nurseries have an enhanced chance of forming large planets. An international team, led by Dr. Marion Villenave of NASA’s Jet Propulsion Laboratory (JPL), has observed a remarkably thin disk of dust and gas around a young star, and found that its structure speeds up the process of grains clumping together to form planets.

“Planets have only a limited chance of forming before the disk of gas and dust dissipates, scattered, by radiation from their parent star. The micron-sized elementary particles that make up the disk must rapidly grow into millimeter-sized grains that are the building blocks of planets. In this thin disk, We can see that the large particles have settled in a dense medium level, due to the combined effect of stellar gravity and interaction with gas, which created very favorable conditions for planetary growth, explained Dr. Villenave.

Using the Atacama Large Millimeter Array (ALMA) in Chile, the team obtained very high-resolution images of the protoplanetary disk Oph163131, located in a nearby star-forming region called Ophiuchus. Their observations showed that while the disk is twice the diameter of our Solar System, the bulk of the dust at its outer edge is vertically concentrated in a layer only half the distance from the Earth to the Sun. This makes it one of the thinnest planetary nurseries ever observed.


“Looking at the protoplanetary disks on the edge gives a clear view of the vertical and radial dimensions, so we can separate the dust evolution processes at work,” Villenev said. “Alma gave us our first look at the distribution of millimeter-sized grains in this disk. Their concentration in such a thin layer was a surprise, as previous Hubble Space Telescope (HST) observations of micron-sized particles showed a region spanning nearly 20 times.”

The team’s simulations based on observations show that the seeds of gas giant planets, which must be at least 10 Earth-masses, could form in the outer part of the disk in less than 10 million years. This is within the typical incubation age of planets before they dissipate.

“Thin planetary nurseries appear to be favorable for the formation of large planets, and may even facilitate the formation of planets at a great distance from the central star,” Villenev said. “Finding more examples of these thin disks may help provide more insights into the predominant mechanisms of how wide-orbiting planets form, an area of ​​research in which many open questions remain.”

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