Comment on What is this odd object in Saturn’s rings? by Snowball Solar System

Core accretion doesn’t work, otherwise chondrules from the early solar system would be variable in size, rather than being small with a distinctive upper size ranges as they indeed are. So “Peggy” can not be an object formed by core accretion any more than planets or exoplanets.

But perhaps a tweaked accretion model may be possible which doesn’t violate the chondrule evidence.

‘Hybrid’ accretion suggested by Thayne Currie, (Hybrid Mechanisms for Gas/Ice Giant Planet Formation, 2005) may form super Earths by core accretion of circa 100 km and larger planetesimals ‘condensed’ by gravitational instability (GI) just beyond the corotation radius of young stellar objects (YSOs), rather than gas/ice giant planets as he suggests.

However, Mars may be the only super-Earth-type planet in our own solar system composed of presolar planetesimals (for reasons not given here).

Proto-planetesimals condensed by GI typically fragment (bifurcate) due to excess angular momentum as they gravitationally contract. Subsequently, external perturbation may cause binary planetesimals to spiral in and merge, initiating aqueous differentiation from the heat of merger released in ‘contact binaries’, during which minerals precipitate and grow in size through crystallization. Negative buoyancy ultimately causes mineral grains to fall out of suspension in the microgravity of salty planetesimal core oceans, forming sedimentary cores. Subsequent diagenesis, lithification and metamorphism convert sedimentary cores to gneiss-dome planetesimal cores with hydrothermal mantle rock.

On Mars, the internal core accretion of mantled-gneiss-dome planetesimal cores may be visible in areas swept clear of basaltic dust, such as, Hellas Basin:

http://hirise.lpl.arizona.edu/images/wallpaper/2048/PSP_008559_1405.jpg

https://farm4.static.flickr.com/3179/2857930291_3e12f007ac_o.jpg

and Melas Chasma:

http://www.psi.edu/sites/default/files/images/staff/mbourke/3_11_Image2.jpg

http://i.dailymail.co.uk/i/pix/2010/09/03/article-0-0B07670A000005DC-728_634x384.jpg