1009 Sirene is a Mars-crosser asteroid. It was discovered by Karl Wilhelm Reinmuth on October 31, 1923, and named after the mythological Sirens. Its provisional designation was 1923 PE. It was a lost asteroid until it was recovered in 1982 from exposures on the 48-inch (120 cm) Schmidt at Palomar Observatory.
Sirene's semi-major axis is 2.63 AU, well beyond that of Mars, but its highly eccentric orbit crosses Mars', allowing close approaches of the planet. It passed inside of 30 Gm 11 times from 1500 to 2500, coming nearest in 1940 at 7.3 Gm.