Today, give attention to energies in your material: speed, friction, attraction, repulsion, heat, spin . . .
Options, depending on what kind of momentum you have:
— Always the option to simply expand. (Remember you can graft a new branch, fill out a thin place, add on to the end or write a prologue. Think spherically when it’s compelling to think that way (spherically as in a planet slowly growing from its center in all directions). When that feels forced or irritating, just write forward.)
— If acquiescing to a structure is working for you, try this: grow a second planetesimal. Following the planetary accretion metaphor, collision will be a feature of the late stages of development. So you build chunk #2 (or #3 if you’ve sprouted other centers already) in preparation for the eventual collision with #1. What is a “second planetesimal”? It could be a new strand of story, a counter narrative, or something that feels totally outside what you’ve written so far. Or maybe you find yourself with lots of weird little lumps of rock with no clear center. That works for the collision course too. If you’ve got lots of little bits and pieces, perhaps choose two to increase in size and write into both over the next few days.