public static String findCollisions(ArrayList<Planet> planets) {
        String collisions = "";

        for (int i = 0; i < planets.size(); i++) {
            for (int j = 0; j < planets.size(); j++) {
                if (i != j) {
                    if (Planet.areColliding(planets.get(i), planets.get(j))) {
                        collisions += "Die Planeten " + planets.get(i).getLabel() + " und " + planets.get(j).getLabel() + " kollidieren.\n";
                        planets.remove(i);
                        i = (i > 0) ? i -= 1 : i;
                        j = (j > 0) ? j -= 1 : j;
                    }
                }
            }
        }

        return collisions;
    }