Periodic Comet Shoemaker-Levy 9 is more akin to a handful of marbles than a baseball.
Each time a
periodic comet revisits the inner solar system, it can experience the gentle effects of dust-bearing gas jets erupting on its sun-warmed surface.
A preceding P means you're looking at a
periodic comet (any comet with an orbital period of 200 years or less).
The Perseids are pieces of
Periodic Comet Swift-Tuttle.
Matese at the University of Southwestern Louisiana in Lafayette created the new theory by merging two ideas that were proposed in the past for reasons totally unrelated to
periodic comet impacts and mass extinctions: a tenth planet, dubbed Planet X and envisioned to reside beyond the orbit of Pluto; and a disk or belt of comets throught to lie in the plane of the solar system beyond Neptune.
Rosetta launched in March 2004, and after a long cruise that included flybys of Earth, Mars, and two asteroids--plus an unnervingly long hibernation period--the spacecraft arrived at its primary target, a
periodic comet called 67P/Churyumov-Gerasimenko, in August 2014.
These
periodic comet showers appear to correlate with the dates of ancient impact craters found on Earth, which would suggest that most impactors in the past were comets, not asteroids.
Periodic comet 41P/Tuttle-Giacobini-Kresak may be reaching 6th or even 5th magnitude very high in the northern evening sky.
According to Nasa, this meteor storm would result "from the dust of
periodic comet 209P/LINEAR, a Jupiter family comet discovered by the Lincoln Laboratory Near-Earth Asteroid Research project in 2004".