Mars and Ceres together

As long as we are what-iffing about Mark, Stephen Kane proposes a what-if about Mars - or rather SuperCeres. I'd started this essay yesterday but waited for more outside commentary before continuing; Paul Gilster thankfully got in on it this morning.

We seem to inhabit an anthropic-principle system wherein, if something more muscular than Ceres and her girlfriends had run into 2 or 3.7 AU for any extent of time... Earth be doomed. SuperVesta and SuperCybele each nudge Jupiter too much. Oddly the 3.7 AU superultraCybele spares Mars. Otherwise both these orbits pull Venus and Earth for eccentricity, so ejecting Mercury before finally dooming Earth.

Let's simplify things: protoplanetary disc doesn't form actual Mars, for a bit. Meanwhile Ceres and Hygiea and so-on find their way into this Belt, earlier. A core then forms at 2.8 AU where it can keep its ice, and wax larger.

I'd counter-argue Kane that even if we tack on extra mass to this chimera, our system might not own sufficient material between 1-5 AU to form a superEarth or, even, an Earth-mass planet. A worldbuilder can tweak Jupiter (and Saturn) to orbit a little further away. And, maybe, let Jupiter be bigger; Saturn smaller. But must he?

This Mars-Ceres hybrid should have eccentricity oh, 0.085 by now, let's say. Total mass maybe 50% Earth's (this is generous: Mars' is only like 10%). Density 3000 kg/m³; differentiated so - fairly high albedo (and we do not name this after our blood god). Core is Marslike maybe a little bigger having sucked in Vesta etc. I don't think it keeps its magnetic field but it might not have to, at this irradiance and greater mass.

Moons: insignificant. Ring-system: possible, mostly ice.

Thick nitrogen atmosphere. Thin CO₂ / H₂O vapour clouds. The greenhouse and the pressure are together insufficient to allow liquid anything on the surface. No subsurface ocean.

I've got this world pulling ice and silicates from where Theia should have formed so, Earth doesn't get as big a Moon.

RELATIVITY 3/9 Another point: relativistic effects on Mercury, as its orbit gets elongated so perihelion shorter. The first planet doesn't trade energy as fast as has been thought. As our system is stable up to the heat-death of its Sun; so would this alt-system be.

SUPERTITAN 5/27 Oh yeah, it'll be carbon-dominant.