164207 Cardea
164207 Cardea is a sub-kilometer asteroid, classified as a near-Earth object and potentially hazardous asteroid of the Apollo group. It is a quasi-satellite of Earth, a situation that should persist until around 2600, when it is expected to shift to a regular horseshoe orbit for a few thousand years.
On 14 April 2004, the Sentry Risk Table showed 180 virtual impactors. It was removed from the Sentry Risk Table 2 days later on 16 April 2004. As later precovery observations by Haleakala-AMOS from 2001 have been found, Cardea now has a well determined orbit with an observation arc of 24 years.
Discovery and naming
This asteroid was discovered on 13 April 2004 by the Lincoln Near-Earth Asteroid Research project near Socorro, New Mexico and given the provisional designation. Following the naming of 524522 Zoozve, a quasi-satellite of Venus, Radiolab and the International Astronomical Union held a public naming campaign for this quasi-satellite from June to September 2024. Seven finalist names were revealed in December 2024, with the names being Bakunawa, Cardea, Ehaema, Enkidu, Ótr, Tarriaksuk, and Tecciztecatl. The winning name was Cardea, the Roman goddess of the hinge. The name was announced by the International Astronomical Union on 13 January 2025.Orbit
Cardea orbits the Sun with a semi-major axis of 1.001 astronomical units, taking 365.87 days to complete one orbit. It is classified as a near-Earth asteroid and an Apollo asteroid; Apollo asteroids are NEAs that cross Earth's orbit but have semi-major axes above 1 AU. Its orbit is inclined by 13.653° with respect to the ecliptic plane. Along its orbit, its distance from the Sun varies from 0.865 AU at perihelion to 1.137 AU at aphelion due to its moderate orbital eccentricity of 0.136.Cardea is in a 1:1 mean-motion resonance with Earth, and it currently orbits in a quasi-satellite configuration. Quasi-satellites have principal libration angles that librate around 0°, appearing to distantly orbit Earth from its perspective despite directly orbiting the Sun. All Earth quasi-satellites are temporary; Cardea has been a quasi-satellite for about 600 years, and will eventually lose its status as one in about 500 years. Perturbations from Venus play a role in destabilizing Cardea from its quasi-satellite configuration even though their orbits do not cross. Currently, the libration of Cardea's has an amplitude of 8–10°, with a libration period of 70 years. After exiting its quasi-satellite phase, it will enter a horseshoe configuration.