Comet Shoemaker–Levy 9 then fell to below pre-impact temperatures 2–3 weeks afterwards, before rising slowly to normal temperatures. SL9 is not unique in having orbited Jupiter for a time; five comets, (including 82P/Gehrels, 147P/Kushida–Muramatsu, and 111P/Helin–Roman–Crockett) are known to have been temporarily captured by the planet. Cometary orbits around Jupiter are unstable, as they will be highly elliptical and likely to be strongly perturbed by the Sun's gravity at apojove (the furthest point on the orbit from the planet). By far the most massive planet in the Solar System, Jupiter can capture objects relatively frequently, but the size of SL9 makes it a
David H. Levy biography of Pluto-discoverer Clyde Tombaugh in 2006, and his tribute to Gene Shoemaker in "Shoemaker by Levy". He has provided periodic articles for "Sky and Telescope" magazine, as well as "Parade Magazine", "Sky News" and, most recently, "Astronomy Magazine". Periodic comets that Levy co-discovered include 118P/Shoemaker–Levy, 129P/Shoemaker–Levy, 135P/Shoemaker–Levy, 137P/Shoemaker–Levy, 138P/Shoemaker–Levy, 145P/Shoemaker–Levy, and 181P/Shoemaker–Levy. In addition, Levy is the sole discoverer of two periodic comets: 255P/Levy and P/1991 L3. On February 28, 2010, Levy was awarded a Ph. D. from the Hebrew University of Jerusalem for his successful completion of his thesis "The Sky in Early Modern English Literature: A Study