1685 Toro

1685 Toro (prov. designation: ) is an asteroid and near-Earth object of the Apollo group on an eccentric orbit. It was discovered on 17 July 1948, by American astronomer Carl Wirtanen at Lick Observatory on Mount Hamilton, California. The stony S-type asteroid has a rotation period of 10.2 hours and measures approximately 4 km in diameter. It is named for Betulia Toro Herrick, wife of astronomer Samuel Herrick. The Sylacauga meteorite appears to have originated from this asteroid.

Classification and orbit
Toro is an Apollo asteroid, a subgroup of near-Earth asteroids that cross the orbit of Earth. It orbits the Sun at a distance of 0.8–2.0 AU once every 584 days. Its orbit has an eccentricity of 0.44 and an inclination of 9° with respect to the ecliptic.

This asteroid's orbit also shows a 5:8 resonance with Earth and a near 5:13 resonance with Venus. This near resonance results from Earth and Venus being in a near 8:13 resonance with each other. It was the third Apollo asteroid to be discovered. The current resonance with Earth will last for only a few thousand years. Calculations show that Toro will leave it in 2960 CE, and that it will enter the region of 5:13 resonance with Venus in 3470 CE. This is because the distance from Earth's orbit will become larger and that from Venus's orbit smaller. A study of long-term stability shows that the alternating resonances will possibly be broken roughly 3 million years from now because of close approaches between Toro and Mars.

Based on orbital paths, Toro is the best candidate for the source of the Sylacauga meteorite, the first meteorite authenticated to have struck a human, Mrs. Ann Hodges of Sylacauga, Alabama on 30 November 1954. Toro's Earth minimum orbit intersection distance of 0.0507 AU, is just above the 0.05 AU requirement to be listed as a potentially hazardous asteroid. With an orbital uncertainty U = 0, its orbit and future close approaches are well determined.

Naming
This minor planet was named after the maiden name of Betulia (née Toro) Herrick, wife of American astronomer Samuel Herrick. Herrick had studied the asteroid's orbit, and requested the name, along with the other asteroid, 1580 Betulia. The official was published by the Minor Planet Center on 10 March 1966 (M.P.C. 2504).

Physical characteristics
In the Tholen and SMASS taxonomic scheme, Toro is characterized as a stony S-type asteroid. It is reported to be composed of L chondrite with a high albedo in the range of 0.24–0.34. It has an extremely well-measured rotation period of 10.2 hours. Its rotation period is slowly increasing due to the YORP effect.