What smacked Uranus on its side? Something icy and as massive as Earth, scientists say.

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FYI, there is more comprehensive studies published on protoplanetary disks and planet evolution in them I read at the NASA ADS site. Planet formation: key mechanisms and global models "Models of planet formation are built on underlying physical processes. In order to make sense of the origin of the planets we must first understand the origin of their building blocks. This review comes in two parts. The first part presents a detailed description of six key mechanisms of planet formation: 1) The structure and evolution of protoplanetary disks 2) The formation of planetesimals 3) Accretion of protoplanets 4) Orbital migration of growing planets 5) Gas accretion and giant planet migration 6) Resonance trapping during planet migration. While this is not a comprehensive list, it includes processes for which our understanding has changed in recent years or for which key uncertainties remain..."

A new model using magnetic fields that Torbjorn mentioned is published, attempting to explain the angular momentum problem of planets like in our solar system. https://phys.org/news/2020-04-simultaneous-simulation-gravitation-magnetism-protoplanetary.html, The cited abstract, https://iopscience.iop.org/article/10.3847/1538-4357/ab77b2, shows some words of caution. "Abstract In the early stages of a protoplanetary disk, turbulence generated by gravitational instability (GI) should feature significantly in the disk's evolution. At the same time, the disk may be sufficiently ionized for magnetic fields to play some role in the dynamics. In this paper, we report on global three-dimensional magnetohydrodynamical simulations of a self-gravitating protoplanetary disk using the meshless finite mass Lagrangian technique...Our simulations use ideal MHD, an admittedly poor approximation in protoplanetary disks, and thus, future studies should explore the full gamut of nonideal MHD. In preparation for that, we exhibit a small number of ohmic runs that reveal that the dynamo, if anything, is stronger in a nonideal environment. This work confirms that magnetic fields are a potentially critical ingredient in gravito-turbulent young disks, possibly controlling their evolution, especially via their enhancement of (potentially episodic) accretion."

Presently there is 4247 confirmed exoplanets now, The Extrasolar Planets Encyclopaedia The general consensus model to explain planet formation seems to offer much but also comes with problems too, just compare the exoplanet inventory known today with our solar system configuration. If I were to compare H-R generated computer diagrams of star clusters with main sequence turn-off points and red giant branch stars to protoplanetary disk modeling from tiny dust grains to fully grown planets and solar systems, the H-R diagram models are on better observational grounds I feel, fewer holes in the modeling and physics. Perhaps a cleaner bill here :)
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Nice post rod.

I recall a "video" from "the astronomy picture of the day" that actually resolved three planets making an "orbital arc" around what must be a fairly close star. Of all these 4247 exoplanets, how many have been "resolved"?

Went back and looked at brown dwarfs after our exchange on comet origins and Wiki tells me the first confirmed exoplanet is actually orbiting a brown dwarf. Is this correct? Seems a likely result as brown dwarfs probably form from the same mechanism as stellar systems.

And surely there must be brown dwarf-stellar binaries, also with planets and discs. We almost got one with Jupiter. (Some would say we do!) Heck, it has the largest moon. And its mag field is enormous. It is almost a minor solar system onto itself.
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dfjchem721 you asked *Of all these 4247 exoplanets, how many have been "resolved"?* 136 are imaged exoplanets meaning they are photographed near their host star. A few examples of imaged exoplanets is DH Tau b, considered about 11 Jupiter masses, Fomalhaut b, about 3 Jupiter masses, and FU Tau b, about 15 Jupiter masses. The three I list here show semi-major axis ranging from 115 AU to 800 AU from their host stars. Another imaged exoplanet is AB Dor C b, about 13 Jupiter masses and semi-major axis 0.58 AU from host star or inside Venus orbit in our solar system.

3031 are primary transit method, and 882 radial velocity, and other methods of detection. I keep this database updated in my home MS ACCESS DB. I run queries and reports using the data so can quickly see various details including using MS SQL descriptive stat queries and charts. The site does have charts too for various parameters you can change. Brown dwarfs are an interesting topic. Exoplanets orbiting a brown dwarf I do have some references in my trusty, home DB :) CFBDS 1458 b reported by Sky & Telescope 121(6):12, 2011, June 2011 News Notes reported. OGLE-2017-BLG-1522 b, reference Astronomers discover a giant planet orbiting a brown dwarf, MOA-2015-BLG-337L, reference Planet orbiting a brown dwarf or a brown dwarf binary? Astronomers use cosmic lens

Keep digging you biochemist :)--Rod
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