Is (1R,3aR,4S,6aS)‐1,4‐dibromo‐octahydropentalene chiral or achiral? Is this molecule on the left chiral or achiral?

I believe it is achiral because its mirror image (on the right) is essentially the same molecule. But I was told that it is chiral because it doesn't have an internal plane of symmetry. Could someone tell me which explanation is correct?
It indeed is achiral, because the red dot is the center of symmetry, hence it is superimposible with its mirror image.
Having an internal plane of symmetry is not the only criterion, the presence of a centre of symmetry also leads to the compound being achiral.