| • Science | • People | • Locations | • Timeline |
| Discovery | |
|---|---|
| Discoverer | J. Duncan Waldron |
| Discovery Date | October 10, 1986 |
| Alternate Designations | 1983 UH; 1986 TO |
| Category | Near-Earth asteroid, Venus-crosser asteroid, Mars-crosser asteroid |
| Orbital Elements Epoch July 14, 2004 ( JD 2453200.5) | |
| Eccentricity (e) | 0.515 |
| Semi-Major Axis (a) | 149.260 G m (0.998 AU) |
| Perihelion (q) | 72.415 Gm (0.484 AU) |
| Aphelion (Q) | 226.104 Gm (1.511 AU) |
| Orbital Period (P) | 364.019 d (1.00 a) |
| Mean Orbital Speed | 29.82 km/ sThis article is about the unit of time. See second (disambiguation) for other uses The second (symbol s is a unit for time, and one of seven SI base units. It is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transi |
| Inclination (i) | 19.810 ° |
| Longitude of the Ascending Node (Ω) | 126.311° |
| Argument of Perihelion (ω) | 43.719° |
| Mean Anomaly (M) | 190.171° |
| Physical Characteristics | |
| Dimensions | ~5 km |
| Mass | 1.3×1014 kgThe kilogram (symbol: kg is the SI base unit of mass. A gram is defined as one thousandth of a kilogram. Conversion of units describes equivalent units of mass in other systems. Multiples SI prefixes are used to name multiples and subdivisions of the kilo |
| Density | 2 ? g/ cCenti can also stand for Centro Internacional de Teoterapia Integral (International Center of Integral Teotheraphy). Centi (symbol c is a SI prefix in the SI system of units denoting a factor of 10-2, or 1/100. Adopted in 1795, the prefix comes from the L m³The cubic metre (symbol m is the SI derived unit of volume. It is the volume of a cube with edges one metre in length. Older, now unofficial, equivalents were the stere and the kilolitre. 1 cubic metre is equal to: 1,000 litres 1,000 cubic decimetres 1, |
| Surface Gravity | 0.0014 m/s² |
| Escape Velocity | 0.0026 km/s |
| Rotation Period | ? d |
| Spectral Class | ? |
| Absolute Magnitude | 15.1 |
| Albedo | 0.15 ? |
| Mean Surface Temperature | ~378 KThe kelvin (symbol: K is the SI unit of temperature, and is one of the seven SI base units. It is defined by two facts: zero kelvin is absolute zero (when molecular motion stops), and one kelvin is the fraction 1/273. 16 of the thermodynamic temperature o |
Cruithne was named after the first Celtic racio-tribal group to inhabit the British Isles. The Cruithne emigrated from the European continent and appeared in Britain between about 800 and 500 B.C. [1] The correct pronunciation for 'Cruithne' is 'croo-een-ya', with the emphasis on the -een-.
Cruithne shares Earth's orbit, but does not actually orbit the Earth. Instead, it follows a spiralling path that moves along the Earth's orbit in a horseshoe shape, the two ends of the horseshoe approaching either side of Earth but not quite reaching it. This orbit sometimes takes it closer to the Sun than Venus, and sometimes halfway to Mars' orbit. It takes Cruithne 385 Earth years to complete one such horseshoe orbit. This orbital path appears extremely complex and non-intuitive when viewed from Earth's frame of reference. It is much easier to understand by recognizing that from the Sun's frame of reference Cruithne follows a relatively conventional orbit which takes almost exactly the same time to complete as Earth's (one year), but which is slightly more elliptical. The gravitational influence of Earth modifies this elliptical orbit only slightly, just enough to modify Cruithne's precession and prevent it from coming too close.
Cruithne is approximately 5 km in diameter, and its closest approach to Earth is 15 million kilometres (approximately 40 times the separation between Earth and the Moon). Although Cruithne's orbit is not thought to be stable over the long term, calculations by Wiegart and Innanen showed that it has likely been in sync with Earth's orbit for a long time. There is no danger of it colliding with Earth for millions of years, if ever. Cruithne is not visible to the naked eye at any point in its orbit.
Three other near-Earth asteroids (NEAs), (54509) 2000 PH5 , (85770) 1998 UP1 and 2002 AA29, which exist in resonant orbits similar to Cruithne's, have since been discovered.
Other examples of natural bodies known to be in horseshoe orbits at the time of writing include Janus and Epimetheus, natural satellites of Saturn. The orbits these two moons follow around Saturn are much simpler than the one Cruithne follows, but operate along the same general principles.
Mars has one known co-orbital asteroid ( 5261 Eureka), and Jupiter has many (about 400 objects, the Trojan asteroids); there are also other small co-orbital moons in the Saturnian system: Telesto and Calypso with Tethys, and Helene with Dione. However, none of these follow horseshoe orbits.Cruithne has been featured in the novel Manifold: Time by science-fiction author Stephen Baxter, perhaps due to its unconventional orbit of Earth.