The Accretion Disc Dynamo in the Solar Nebula

The nearest accretion disc to us in space if not time was the protosolar nebula. Remnants of this nebula thus potentially offer unique insight into how discs work. In particular the existence of chondrules, which must have formed in the disc as small molten droplets, requires strong and intermittent heating of disc material. We argue that this places important constraints on the way gravitational energy is released in accretion discs, which are not met by current shearing–box simulations of MRI–driven dynamos. A deeper understanding of accretion energy release in discs may require a better model for these dynamos.