Yarkovsky-O'Keefe-Radzievskii-Paddack effect

Yarkovsky-O'Keefe-Radzievskii-Paddack effect

The Yarkovsky-O'Keefe-Radzievskii-Paddack effect, or YORP effect for short, is a second-order variation on the Yarkovsky effect which changes the rotation rate of a small body (such as an asteroid). The term was coined by Dr. David P. Rubincam in 2000.

In the 19th century, Yarkovsky realised that the infrared radiation escaping from a body warmed by the Sun carries off momentum as well as heat. Translated into modern physics, each photon escaping carries away a momentum "p" = "E/c" where "E" (="hν") is its energy and "c" is the speed of light. Radzievskii applied the photon idea to rotation based on changes in albedo [Radzievskii (1954) below] and Paddack and O'Keefe realised that shape was a much more effective means of altering a body's spin rate. Paddack and Rhee suggested that the YORP effect may be the cause of rotational bursting and eventual elimination from the solar system of small asymmetric particles [S. J. Paddack, J. W. Rhee, "Geophys. Res. Lett" 2, 365 (1975)]

In 2007 there was direct observational confirmation of the YORP effect on the small asteroids 54509 YORP (then named mpl|2000 PH|5) [S. C. Lowry "et al., Science" 316 272 (2007) and P. A. Taylor "et al., Science" 316 274 (2007)] and 1862 Apollo [M. Kaasalainen "et al., Nature" 446, 420 (2007)] . The spin rate of 54509 YORP will double in just 600,000 years, and the YORP effect can also alter the axial tilt and precession rate, so that the entire suite of YORP phenomena can send asteroids into interesting resonant spin states, and helps explain the existence of binary asteroids [D. P. Rubincam and S. J. Paddack, "Science" 316 211 (2007)]

Observations show that asteroids larger than 125 km in diameter have rotation rates that follow a Maxwellian frequency distribution, while smaller asteroids (in the 50 to 125 km size range) show a small excess of fast rotators. The smallest asteroids (size less than 50 km) show a clear excess of very fast and slow rotators, and this becomes even more pronounced as smaller populations are measured. These results suggest that one or more size-dependent mechanisms are depopulating the centre of the spin rate distribution in favour of the extremes. The YORP effect is a prime candidate. It is not capable of significantly modifying the spin rates of large asteroids by itself, however, so a different explanation must be sought for objects such as 253 Mathilde.


Assume a rotating spherical asteroid has two wedges attached to its equator. The reaction force from photons departing from any given surface element of the sphere will be normal to the surface, such that no torque is produced. Energy reradiated from the wedges, however, can produce a torque because the wedge faces are not parallel to the sphere's surface. An object with some "windmill" asymmetry can therefore be subjected to minuscule torque forces that will tend to spin it up or down as well as make its axis of rotation precess.

Note that the YORP effect is zero for a rotating ellipsoid "if" there are no irregularities in surface temperature or albedo.

In the long term, the object's changing obliquity and rotation rate may wander randomly, chaotically or regularly, depending on several factors. For example, assuming the Sun remains on its equator, asteroid 951 Gaspra, with a radius of 6 km and a semi-major axis of 2.21 AU, would in 240 Ma (240 million years) go from a rotation period of 12 h to 6 h and vice versa. If 243 Ida were given the same radius and orbit values as Gaspra, it would spin up or down twice as fast, while a body with Phobos' shape would take several billion years to change its spin by the same amount.

Size as well as shape affects the amount of the effect. Smaller objects will spin up or down much more quickly. If Gaspra were smaller by a factor of 10 (to a radius of 500 m), its spin will halve or double in just a few million years. Similarly, the YORP effect intensifies for objects closer to the Sun. At 1 AU, Gaspra would double/halve its spin rate in a mere 100,000 years. After one million years, its period may shrink to ~2 h, at which point it could start to break apart.

This is one mechanism through which binary asteroids may form, and it may be more common than collisions and planetary near-encounter tidal disruption as the primary means of binary formation.

Asteroid mp|2000 PH|5 was later named 54509 YORP to honor its part in the confirmation of this phenomenon.

Notes & References

* O'Keefe, John A., "Tektites and Their Origin", Elsevier, Amsterdam. 254 pp. (1976)
* Paddack, Stephen J., "Rotational bursting of small celestial bodies: Effects of radiation pressure", J. Geophys. Res., 74, 4379–4381 (1969)
* Radzievskii, V. V., "A mechanism for the disintegration of asteroids and meteorites", Dokl. Akad. Nauk SSSR, 97, 49–52 (1954)
* Rubincam, David P., "Radiative spin-up and spin-down of small asteroids", Icarus, 148, 2–11 (2000)

External links

* http://dsc.discovery.com/news/2007/03/07/asteroidspin_spa.html?category=space&guid=20070307130000&dcitc=w19-502-ak-0000
* [http://skytonight.com/news/wires?id=104027525&c=y Asteroid rotation discovery reported]

ee also

* Yarkovsky effect

Wikimedia Foundation. 2010.

Игры ⚽ Нужен реферат?

Look at other dictionaries:

  • Effet Yarkovsky-O'Keefe-Radzievskii-Paddack — Effet YORP En astrophysique, l’effet Yarkovsky O Keefe Radzievskii Paddack souvent abrégé effet YORP est un phénomène qui explique les modifications de la rotation de certains astéroïdes relativement petits[1]. Il apparaît comme une approximation …   Wikipédia en Français

  • Ivan Osipovich Yarkovsky — ( Iwan Osipowicz Jarkowski , 1844 1902) was a Russian Polish civil engineer. He worked for a Russian railway company and was obscure in his own time. Beginning in the 1970s, his work on the effects of thermal radiation on small objects in the… …   Wikipedia

  • Effet YORP — En astrophysique, l’effet Yarkovsky O Keefe Radzievskii Paddack souvent abrégé effet YORP est un phénomène qui explique les modifications de la rotation de certains astéroïdes relativement petits[1]. Il apparaît comme une approximation à l ordre… …   Wikipédia en Français

  • List of effects — This is a list of names for observable phenonema that contain the word effect, amplified by reference(s) to their respective fields of study. #*3D audio effect (audio effects)A*Accelerator effect (economics) *Accordion effect (physics) (waves)… …   Wikipedia

  • Mikko Kaasalainen — Mikko K.J. Kaasalainen is a Finnish applied mathematician and mathematical physicist. He is currently professor of mathematics at the department of mathematics at Tampere University of Technology. Kaasalainen has mostly worked on inverse problems …   Wikipedia

  • Binary asteroid — A binary asteroid is a system of two asteroids orbiting their common center of mass, in analogy with binary stars. 243 Ida was the first binary asteroid to be identified when the Galileo spacecraft did a flyby in 1993. Since then numerous binary… …   Wikipedia

  • Minor planet moon — 243 Ida and its moon Dactyl as imaged by the Galileo spacecraft in 1993 …   Wikipedia

  • Asteroid moon — An asteroid moon is an asteroid that orbits another asteroid as its natural satellite. It is thought that many asteroids may possess moons, in some cases quite substantial in size. Discoveries of asteroid moons (and binary objects, in general)… …   Wikipedia

  • Efecto Yorp — Saltar a navegación, búsqueda El Efecto Yarkovsky O Keefe Radzievskii Paddack, o efecto Yorp, es una variación de segundo orden del Efecto Yarkovsky que causa que un cuerpo pequeño (como un asteroide) gire muy rápido o muy lento. El término lo… …   Wikipedia Español

  • YORP — Der Yarkovsky O Keefe Radzievskii Paddack Effekt, verkürzt auch YORP Effekt genannt, ist eine allmähliche Veränderung des Rotationszustands kleiner Körper (z. B. von Asteroiden) unter dem Einfluss der Sonnenstrahlung. Beschreibung Wie der… …   Deutsch Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”