  We present results from our 47-night imaging campaign of Comet
41P/Tuttle-Giacobini-Kresak conducted from Lowell Observatory between 2017
February 16 and July 2. Coma morphology revealed gas jets, whose appearance and
motion as a function of time yielded the rotation period and other properties.
All narrowband CN images exhibited either one or two jets; one jet appeared as
a partial face-on spiral with clockwise rotation while the second jet evolved
from a side-on corkscrew, through face-on, and finally corkscrew again, with
only a slow evolution throughout the apparition due to progressive viewing
geometry changes. A total of 78 period determinations were made over a 7-week
interval, yielding a smooth and accelerating rotation period starting at 24 hr
(March 21&22) and passing 48 hr on April 28. While this is by far the fastest
rate of change ever measured for a comet nucleus, the torque required is
readily within what can exist given likely properties of the nucleus. If the
torque remained constant, we estimate that the nucleus could have stopped
rotating and/or began to tumble as soon as only two months following
perihelion, and will certainly reach this stage by early in the next
apparition. Working backwards in time, Tuttle-Giacobini-Kresak would have been
rotating near its rotational break-up velocity 3-4 orbits earlier, suggesting
that its extreme 7-magnitude outburst observed in 2001 might have been caused
by a partial fragmentation at that time, as might the pair of 1973 8-magnitude
outbursts if there had been an earlier spin-down and spin-up cycle.
