where is the dark mass? April Fools

The day began with a call with Ana Bonaca (Harvard), in which she showed me that she can take her models of the GD-1 stream perturbation and predict the present-day location of the substructure (or dark mass) that created the perturbation. Because the model space is broad, the “error box” is large, but the fact that we have such a prediction is fun, and interesting. All this progress flows from the fact that we now have some radial-velocity data on the stream and the spur (which is the feature we think was raised by a dark-matter interaction).

On the arXiv today were the annual set of April Fools papers. My loyal reader knows that I love papers in this category when they are silly or funny but in fact contain an interesting or important calculation or inference. There were two in this category today with Flatiron origins. One was Luger et al, inferring the mean cloud cover on Earth from systematic effects in the NASA TESS imaging! Another was Burns et al, showing that instead of “cubing the sphere” (what climate modelers do to avoid spherical coordinate singularities in discretization) you can “sphere the cube” (embed a cubical simulation volume in a natively spherical-representation simulation). This latter project was ridiculous, but it showed very dramatically that they have a representation for simulating spherical domains with no singularity anywhere (and especially not at the center of the sphere, and at no angular position on the surface).