Oh boy … I suppose the 'spin' I gave this thread was somewhat sceptical, but I do have my limits !
Alex .. DM is hypothetical .. no one argues that point.
The reason it exists in scientific circle discussions, is because it is predicted by theories based on empirical evidence. It is not therefore, pure 'speculation'.
No one has said that the Pioneer anomaly has no physical explanations. This is still under analysis, based on empirical data.
I have never seen any scientist say that 'attraction is the force behind gravity'.
And isn't it great that scientists can still maintain the 'mystery' of DM by publishing these kinds of papers ! It shows they have maintained an 'even keel' and are well balanced individuals !
Cheers