Camera could be gimbal mounted, behind a fixed glass dome - if the speck is on the dome and the camera gimbal moves, it would appear like "the UFO" rotating.
Also what is an ASA.
(I think the speck would have to be on the lens itself though; a speck on the dome would stay fixed during gimbal rotation. Speck on the lens rotates by virtue of the DSP compensating for the camera rotation to keep the world level.)
I suppose also the "shape" of the object could be lens flare (or another imaging artifact) due to the object being very bright. At least some portion of such an artifact would track with the lens as well.
Also, the "halo" effect is an artifact of the imaging system I'm told.
So just because the object is hotter than the sky & clouds doesn't mean much. It could be "room temperature" (say, an insect or fresh bird poo). Or it could be reflective, and simply be reflecting the heat of the plane or camera itself.
What would be helpful is to know the range of temperatures represented by that image. The object is overexposed, so at least we could get a lower bound on its temperature.