I am writing a paper talking about collisions during the formation of rocky planets. Some of these collisions lead to an increase in mass (i.e., the largest body to come out of a collision is more massive than either of the two bodies that were involved in the collision) and some collisions lead to a decrease in mass (i.e., the largest body to come out of a collision is less massive than either of the two bodies that were involved in the collision. I want a word to describe the second case, that the collision led to things getting smaller.

So far I have been using the word "erode" and its various forms, but "erode" means to make smaller over course of time, which doesn't match the situation I am trying to describe. Collisions are discrete (rather than continuous) events, and occur relatively quickly, such that the mass loss is nearly instantaneous. What would be a good word to describe this?

  • What word do you use for increase? – J. Taylor Feb 9 '17 at 19:37
  • @J.Taylor increase and growth, sometimes (particular for collisions that lead to complete mergers of the two bodies) coalesce or merge – NeutronStar Feb 9 '17 at 20:05
  • 3
    Consider "fragmentation", "disintegration" or "disaggregation". – Graffito Feb 9 '17 at 20:14
  • Collision-grown and collision-reduced. Or collision-gained mass and collision-lost mass. – Yosef Baskin Feb 9 '17 at 20:40

This sounds like a spallation process.


Spallation is a process in which fragments of material (spall) are ejected from a body due to impact or stress.

In the case the OP describes, both bodies undergo extensive spallation. The result is a mess of debris and one (or possibly more than one) largish body, all of which are smaller than either of the originals.


The word smash would fit very closely. From Oxford Dictionaries:

  1. [with object] Violently break (something) into pieces:
  1. 1 [no object] Be violently broken into pieces; shatter:

and also

  1. [no object, with adverbial of direction] Move so as to hit or collide with something with great force and impact

Your objects are being smashed into pieces in sense 1 as a result of smashing into one another in sense 2.

The term is a little on the informal side, but it fits your needs closely enough that I think it could easily be used and would seem natural in-context. (There is a history of informal words being used with a technical definition in scientific terminology, as for example fuzzy mathematics or particle strangeness, so maybe you could even define a new term.)


If increase is used for a particle becoming larger, then

The particle (or body) was diminished by the impact


The particle (or body) was decreased by the impact.

That keeps things simple, and that is usually good.

  • But in the case of a particularly nasty collision, there is a lot of fragmentation and not really a body after the collision that I can say is the same body as the one before the collision, just smaller. – NeutronStar Feb 9 '17 at 22:07
  • I think I understand that, Joshua. A apologize for not immediately catching the query beyond "two bodies". . – J. Taylor Feb 9 '17 at 22:17

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