164207 Cardea

164207 Cardea

Cardea photographed by the Canada–France–Hawaii Telescope in February 2007
Discovery [1]
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 [2]
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 [3] : 2988
Geometric albedo	0.219 [3] : 2988
Absolute magnitude (H)	21.1 [2]

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 ${\displaystyle \sigma =\lambda -\lambda _{p}}$ ^[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 ${\displaystyle \sigma }$ 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

See also

• (277810) 2006 FV35 , another quasi-satellite of Earth

Notes

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

References

1. "(164207) = 2004 GU9". Minor Planet Center. Retrieved 3 June 2024.
2. "164207 Cardea (2004 GU9)". JPL Small-Body Database . Jet Propulsion Laboratory. SPK-ID:  2164207 . Retrieved 1 November 2025.
3. 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 .
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.
5. "Major News about Minor Objects: Risk monitoring". hohmanntransfer. 14 April 2004. Archived from the original on 6 November 2020. Retrieved 2 March 2015.
6. "Date/Time Removed". NASA/JPL Near-Earth Object Program Office. Archived from the original on 2 June 2002. Retrieved 1 March 2015.
7. "Competition Announced to Name a Quasi-Moon". IAU. 31 May 2024. Retrieved 3 June 2024.
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).
9. Wall, Mike (2 December 2024). "Strange "quasi-moon" of Earth will get one of these 7 names". Space.com. Retrieved 13 January 2025.
10. "WGSBN Bulletin Volume 5, #1" (PDF). WGSBN Bulletin. 5 (1). International Astronomical Union: 28. 13 January 2025. Retrieved 13 January 2025.
11. "NEO Groups". NASA/JPL Near-Earth Object Program Office. Archived from the original on 2 February 2002. Retrieved 4 June 2012.
12. 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