  Long period comet C/2021 A1 (Leonard) will approach Venus to within 0.029 au
on 2021 December 18 and may subsequently graze the planet with its dust trail
less than two days later. We observed C/2021 A1 with the Lowell Discovery
Telescope on 2021 January 13 and March 3, as well as with the Palomar Hale
Telescope on 2021 March 20, while the comet was inbound at heliocentric
distances of r=4.97 au, 4.46 au, and 4.28 au, respectively. Tail morphology
suggests that the dust is optically dominated by ~0.1-1 mm radius grains
produced in the prior year. Neither narrowband imaging photometry nor
spectrophotometry reveal any definitive gas emission, placing 3-sigma upper
bounds on CN production of <1e23 molec/s at both of the latter two epochs.
Trajectory analysis indicates that large (>1 mm) grains ejected at extremely
large heliocentric distances (r>30 au) are most strongly favored to reach
Venus. The flux of such meteors on Venus, and thus their potential direct or
indirect observability, is highly uncertain as the comet's dust production
history is poorly constrained at these distances, but will likely fall well
below the meteor flux from comet C/2013 A1 (Siding Spring)'s closer encounter
to Mars in 2014, and thus poses negligible risk to any spacecraft in orbit
around Venus. Dust produced in previous apparitions will not likely contribute
substantially to the meteor flux, nor will dust from any future activity apart
from an unlikely high speed (>0.5 km/s) dust outburst prior to the comet
reaching r~2 au in 2021 September.
