1009 Sirene is a Mars-crosser asteroid

Mars-crosser asteroid

A Mars-crosser is an asteroid whose orbit crosses that of Mars. The known numbered Mars-crossers are listed here. They include the two numbered Mars trojans 5261 Eureka and ....

. It was discovered by Karl Wilhelm Reinmuth

Karl Wilhelm Reinmuth

Karl Wilhelm Reinmuth was a German astronomer.He was a prolific discoverer of asteroids , beginning with 796 Sarita in 1914, working at the Landessternwarte Heidelberg-Königstuhl astronomical observatory on the Königstuhl hill above Heidelberg, Germany from 1912 to 1957.His most notable...

 on October 31, 1923, and named after the mythological Siren

Siren

In Greek mythology, the Sirens were three dangerous mermaid like creatures, portrayed as seductresses who lured nearby sailors with their enchanting music and voices to shipwreck on the rocky coast of their island. Roman poets placed them on an island called Sirenum scopuli...

s. 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

Palomar Observatory

Palomar Observatory is a privately owned observatory located in San Diego County, California, southeast of Pasadena's Mount Wilson Observatory, in the Palomar Mountain Range. At approximately elevation, it is owned and operated by the California Institute of Technology...

.

Sirene's semi-major axis

Semi-major axis

The major axis of an ellipse is its longest diameter, a line that runs through the centre and both foci, its ends being at the widest points of the shape...

 is 2.63 AU

Astronomical unit

An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....

, 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.