164207 Cardea

164207 Cardea
	Cardea photographed by the Canada–France–Hawaii Telescope in February 2007
Discovery
Discovered by	LINEAR
Discovery site	Lincoln Lab's ETS
Discovery date	13 April 2004
Designations
MPC designation	(164207) Cardea
Pronunciation	/ˈkɑːrdiə/
Named after	Cardea
Alternative designations	2004 GU9
Minor planet category	NEO · Apollo
Orbital characteristics
	Epoch 21 November 2025 (JD 2461000.5)
	Uncertainty parameter 0
Observation arc	8688 days (23.79 yr)
Aphelion	1.1372 AU (170.12 Gm)
Perihelion	0.8650 AU (129.40 Gm)
Semi-major axis	1.0011 AU (149.76 Gm)
Eccentricity	0.1359
Orbital period (sidereal)	1.0017 yr (365.87 d)
Mean anomaly	97.3298°
Mean motion	0° 59m 1.464s / day
Inclination	13.6529°
Longitude of ascending node	38.3866°
Longitude of perihelion	280.55672±0.00007°
Time of perihelion	2456145.53817±0.00006 jd
Argument of perihelion	279.3410°
Earth MOID	0.0031 AU (460,000 km)
Physical characteristics
Mean diameter	163 m
Geometric albedo	0.219
Absolute magnitude (H)	21.1

164207 Cardea (provisional designation 2004 GU₉) is a sub-kilometer asteroid, classified as 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.^[4]

On 14 April 2004 (with less than a 1-day observation arc), the Sentry Risk Table showed 180 virtual impactors.^[5] It was removed from the Sentry Risk Table 2 days later on 16 April 2004.^[6] 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.^[1]

Discovery and naming

This asteroid was discovered on 13 April 2004 by the Lincoln Near-Earth Asteroid Research (LINEAR) project near Socorro, New Mexico and given the provisional designation 2004 GU₉.^[1] 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.^[7]^[8] Seven finalist names were revealed in December 2024, with the names being Bakunawa, Cardea, Ehaema, Enkidu, Ótr, Tarriaksuk, and Tecciztecatl.^[9] The winning name was Cardea, the Roman goddess of the hinge. The name was announced by the International Astronomical Union on 13 January 2025.^[10]

Orbit

Cardea orbits the Sun with a semi-major axis of 1.001 astronomical units (AU), taking 365.87 days to complete one orbit. It is classified as a near-Earth asteroid (NEA) and an Apollo asteroid;^[2] Apollo asteroids are NEAs that cross Earth's orbit but have semi-major axes above 1 AU.^[11] 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^[3]^: 2987 orbital eccentricity of 0.136.^[2]

Cardea is in a 1:1 mean-motion resonance with Earth, and it currently orbits in a quasi-satellite configuration.^[4]^: 489 Quasi-satellites have principal libration angles $\sigma =\lambda -\lambda _{p}$ ^[a] that librate around 0°,^[4]^: 488 appearing to distantly orbit Earth from its perspective despite directly orbiting the Sun. All Earth quasi-satellites are temporary;^[12] 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 $\sigma$ 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.^[4]^{: 490–491}

Physical characteristics

Cardea has a diameter of 163 metres (535 ft) and an albedo of 0.219.^[3]^: 2988

Animation of 164207 Cardea's orbit from 1600 to 2500

Relative to Sun and Earth

Around Earth

Around Sun

Sun · Earth · Cardea

Notes

^ Where $\lambda$ and $\lambda _{p}$ are the mean longitudes of Cardea and Earth, respectively

References

^ ^a ^b ^c "(164207) = 2004 GU9". Minor Planet Center. Retrieved 3 June 2024.
^ ^a ^b ^c ^d "164207 Cardea (2004 GU9)". JPL Small-Body Database. Jet Propulsion Laboratory. SPK-ID: 2164207. Retrieved 1 November 2025.
^ ^a ^b ^c ^d de la Fuente Marcos, C.; de la Fuente Marcos, R. (21 October 2014). "Asteroid 2014 OL₃₃₉: yet another Earth quasi-satellite". Monthly Notices of the Royal Astronomical Society. 445 (3): 2985–2994. arXiv:1409.5588. Bibcode:2014MNRAS.445.2961D. doi:10.1093/mnras/stu1978.
^ ^a ^b ^c ^d Wajer, Paweł (October 2010). "Dynamical evolution of Earth's quasi-satellites: 2004 GU₉ and 2006 FV₃₅". Icarus. 209 (2): 488–493. Bibcode:2010Icar..209..488W. doi:10.1016/j.icarus.2010.05.012.
^ "Major News about Minor Objects: Risk monitoring". hohmanntransfer. 14 April 2004. Archived from the original on 6 November 2020. Retrieved 2 March 2015.
^ "Date/Time Removed". NASA/JPL Near-Earth Object Program Office. Archived from the original on 2 June 2002. Retrieved 1 March 2015.
^ "Competition Announced to Name a Quasi-Moon". IAU. 31 May 2024. Retrieved 3 June 2024.
^ "OFFICIAL RULES: Name a Quasi Moon!". Radiolab. Retrieved 3 June 2024. Radiolab is partnering with the International Astronomical Union to launch a months-long global naming contest for one of Earth's quasi-moons (asteroid 164207).
^ Wall, Mike (2 December 2024). "Strange "quasi-moon" of Earth will get one of these 7 names". Space.com. Retrieved 13 January 2025.
^ "WGSBN Bulletin Volume 5, #1" (PDF). WGSBN Bulletin. 5 (1). International Astronomical Union: 28. 13 January 2025. Retrieved 13 January 2025.
^ "NEO Groups". NASA/JPL Near-Earth Object Program Office. Archived from the original on 2 February 2002. Retrieved 4 June 2012.
^ Stahl, Asa (21 May 2024). "Earth's quasi-moons, minimoons, and ghost moons". The Planetary Society. Archived from the original on 2 October 2025. Retrieved 3 October 2025.

External links

Dynamical evolution of Earth’s quasi-satellites: 2004 GU9 and 2006 FV35 by Wajer, P. 2010, Icarus, Volume 209, Issue 2, pp. 488–493.
164207 Cardea at NeoDyS-2, Near Earth Objects—Dynamic Site
- Ephemerides · Observation prediction · Orbital info · MOID · Proper elements · Observational info · Close approaches · Physical info · Orbit animation
164207 Cardea at ESA–space situational awareness
- Ephemerides · Observations · Orbit · Physical properties · Summary
164207 Cardea at the JPL Small-Body Database
- Close approach · Discovery · Ephemeris · Orbit viewer · Orbit parameters · Physical parameters

[12] Where $\lambda$ and $\lambda _{p}$ are the mean longitudes of Cardea and Earth, respectively

[MPC-object-1] "(164207) = 2004 GU9". Minor Planet Center. Retrieved 3 June 2024.

[JPL-2] "164207 Cardea (2004 GU9)". JPL Small-Body Database. Jet Propulsion Laboratory. SPK-ID: 2164207. Retrieved 1 November 2025.

[Marcos2014-3] ^ ^a ^b ^c ^d de la Fuente Marcos, C.; de la Fuente Marcos, R. (21 October 2014). "Asteroid 2014 OL₃₃₉: yet another Earth quasi-satellite". Monthly Notices of the Royal Astronomical Society. 445 (3): 2985–2994. arXiv:1409.5588. Bibcode:2014MNRAS.445.2961D. doi:10.1093/mnras/stu1978.

[Wajer2010-4] Wajer, Paweł (October 2010). "Dynamical evolution of Earth's quasi-satellites: 2004 GU₉ and 2006 FV₃₅". Icarus. 209 (2): 488–493. Bibcode:2010Icar..209..488W. doi:10.1016/j.icarus.2010.05.012.

[hohmanntransfer-5] "Major News about Minor Objects: Risk monitoring". hohmanntransfer. 14 April 2004. Archived from the original on 6 November 2020. Retrieved 2 March 2015.

[removed-6] "Date/Time Removed". NASA/JPL Near-Earth Object Program Office. Archived from the original on 2 June 2002. Retrieved 1 March 2015.

[IAU-20240531-7] "Competition Announced to Name a Quasi-Moon". IAU. 31 May 2024. Retrieved 3 June 2024.

[namingcontest-8] "OFFICIAL RULES: Name a Quasi Moon!". Radiolab. Retrieved 3 June 2024. Radiolab is partnering with the International Astronomical Union to launch a months-long global naming contest for one of Earth's quasi-moons (asteroid 164207).

[namefinalists-9] Wall, Mike (2 December 2024). "Strange "quasi-moon" of Earth will get one of these 7 names". Space.com. Retrieved 13 January 2025.

[WGSBN-V5-1-10] "WGSBN Bulletin Volume 5, #1" (PDF). WGSBN Bulletin. 5 (1). International Astronomical Union: 28. 13 January 2025. Retrieved 13 January 2025.

[NEO-groups-11] "NEO Groups". NASA/JPL Near-Earth Object Program Office. Archived from the original on 2 February 2002. Retrieved 4 June 2012.

[TPS20240521-13] Stahl, Asa (21 May 2024). "Earth's quasi-moons, minimoons, and ghost moons". The Planetary Society. Archived from the original on 2 October 2025. Retrieved 3 October 2025.

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