c) The planetoid is being attracted toward another massive object.
Explanation:
We can rule out a, the planetoid is travelling through space, friction is effectively nonexistent. B can be ruled out as well, as there is nothing in space that could naturally repel a planetoid. D is also implausible, as the question says the planetoid slows down for a certain period in its orbit, suggesting this behavior is repeated. Option c is incredibly likely, as the planetoid is far from the sun, a large mass, possibly far smaller than the sun but also far closer to the planetoid, could have the effect described in the question.
