From astrobites: “Can gas giant planets form through pebble accretion?”

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Astrobites

Sep 13, 2017
Michael Hammer

Title: How cores grow by pebble accretion
Authors: Mark Brouwers, Allona Vazan, Chris Ormel
First Author’s Institution: Anton Pannekoek Institute, University of Amsterdam
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Status: Submitted to A&A [open access]

Do you know how gas giant planets form in a protoplanetary disk? It all starts with a bunch of planetesimals (km-sized and above) that collide together one-by-one until they grow into an object that is the largest in the neighborhood. As the biggest object in its vicinity, this protoplanet core will naturally continue to collect and accrete more planetesimals until it consumes everything nearby. Eventually, the core will grow large enough to build up a significant atmosphere from the gas that makes up the disk. Once its atmosphere becomes more massive than the core itself, it will become unstable and devour a ton more gas — thereby growing to roughly Jupiter’s size.

If anyone tells you they know how gas giants form and provides an explanation of the process (like I did above), it might be a good idea to ask them: How long does that process take? Protoplanetary disks – a gas giant’s source of gas – only live about 3 million years on average. Yet, the original model (a classic paper by Pollack et al. from 1996) for this process (called core accretion) suggested it should take 8 million years. While recent improvements to the model have proposed ways to accelerate this process, it is still an open question as to how to speed up core accretion so that it can create Jupiter-mass planets before the disk fades away (see Figure 1).

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Figure 1. The structure of Jupiter, a gas giant planet. Before it accretes all of that hydrogen gas from the protoplanetary disk, it must first assemble a solid core, and do so before the disk dissipates.

See the full article here .

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