Gas released from fresh ice on the illuminated hemisphere can push millimeter-scale grains out at a few m/s, and since these particles weigh thousands of times

Gas released from fresh ice on the illuminated hemisphere can push millimeter-scale grains out at a few m/s, and since these particles weigh thousands of times more than typical cometary dust, solar radiation pressure at 3 au is too weak to bend their trajectories, letting them overtake the nucleus and form a sunward anti-tail. Finson–Probstein dust dynamics predicts this plume should flip to the normal anti-solar direction or fade once 3I/ATLAS moves inside 1 au later this year. Watch the position angle around September to see the theory tested.