hubieran colisionado
-they/you had collided
Past perfect subjunctiveellos/ellas/ustedesconjugation ofcolisionar.

colisionar

Y entonces otro dijo: ¿qué pasaría si la estrella tuviera planetas ya formados, y dos de estos planetas hubieran colisionado, similar a la formación de la Tierra-Luna.
And then somebody else said, well, what if the star had already formed planets, and two of these planets had collided, similar to the Earth-Moon forming event.
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