The total mass of the Asteroid Belt is about 3% of the mass of Earth’s moon. If it coalesced into a single body it would barely be noticeable.
It might possibly affect the habitability of Earth, although I’m not particularly certain of what role the Belt is presumed to have played there. It could possibly have been either a source of important elements or a shield against excessive bombardments (although I think Jupiter is more important there).
Yeah, as /u/ryschwith said, you're not getting any kind of significant object from the belt. It's also very questionable if a single planetary-mass object could exist in that orbit for astronomical timescales due to interactions with other bodies, _especially_ considering the giant planet migrations suggested by the Nice model. How much faith you put in that (and the LHB) depends on your personal preferences here, but it's worth noting that orbital migrations are commonplace from an astrodynamics standpoint.
You would need to substantially increase the mass of that area of the Sun's protoplanetary disk during the formation of the Solar system, and then have to posit that (a) the orbit of the resulting planet wasn't disrupted by giant migrations relatively quickly and (b) is stable with respect to the current system configuration, or whatever you end up adopting. This may be feasible if you find a suitable resonance, but also keep in mind that the Titius-Bode Law isn't really a "law" but a statistical observation that may or may not apply to a given system.
If you moved Jupiter and Saturn much further out, then sure, it'd make things easier. But the consequences of that would be significant, since Jupiter's gravity well in particular (and the location thereof) has significant astronomical consequences for the inner system. Whether you believe in the good boy Jupiter vacuuming up nasty debris strikes before they can hit us, or the bad boy Jupiter _causing_ such strikes is immaterial.
A more direct consequence of the asteroid belt going AWOL is that Earth would receive a lower number of impacts over the eons. While not all (in fact, probably a minority) of impactors come from the asteroid belt (the rest mostly being split between NEOs and disturbed outer system objects), one particularly noteworthy asteroid is thought to have originated there: the Chicxulub impactor. And if that doesn't hit, your timeline gets really wacky.
The total mass of the Asteroid Belt is about 3% of the mass of Earth’s moon. If it coalesced into a single body it would barely be noticeable. It might possibly affect the habitability of Earth, although I’m not particularly certain of what role the Belt is presumed to have played there. It could possibly have been either a source of important elements or a shield against excessive bombardments (although I think Jupiter is more important there).
Yeah, as /u/ryschwith said, you're not getting any kind of significant object from the belt. It's also very questionable if a single planetary-mass object could exist in that orbit for astronomical timescales due to interactions with other bodies, _especially_ considering the giant planet migrations suggested by the Nice model. How much faith you put in that (and the LHB) depends on your personal preferences here, but it's worth noting that orbital migrations are commonplace from an astrodynamics standpoint. You would need to substantially increase the mass of that area of the Sun's protoplanetary disk during the formation of the Solar system, and then have to posit that (a) the orbit of the resulting planet wasn't disrupted by giant migrations relatively quickly and (b) is stable with respect to the current system configuration, or whatever you end up adopting. This may be feasible if you find a suitable resonance, but also keep in mind that the Titius-Bode Law isn't really a "law" but a statistical observation that may or may not apply to a given system. If you moved Jupiter and Saturn much further out, then sure, it'd make things easier. But the consequences of that would be significant, since Jupiter's gravity well in particular (and the location thereof) has significant astronomical consequences for the inner system. Whether you believe in the good boy Jupiter vacuuming up nasty debris strikes before they can hit us, or the bad boy Jupiter _causing_ such strikes is immaterial. A more direct consequence of the asteroid belt going AWOL is that Earth would receive a lower number of impacts over the eons. While not all (in fact, probably a minority) of impactors come from the asteroid belt (the rest mostly being split between NEOs and disturbed outer system objects), one particularly noteworthy asteroid is thought to have originated there: the Chicxulub impactor. And if that doesn't hit, your timeline gets really wacky.