The cause of the outburst is not definitely known. The huge cloud of gas and dust may have resulted from a collision with a meteoroid, or, more probably, from a build-up of gas inside the comet's nucleus that eventually broke through the surface. However, researchers at the Max Planck Institute suggest in a paper published in "Astronomy and Astrophysics" that the brightening can be explained by a thick, air-tight dust cover and the effects of H2O sublimation, with the comet's porous structure providing more surface area for sublimation, up to one order of magnitude greater. Energy from the Sun – insolation – was stored in the dust cover and the nucleus within the months before the outburst.