משתמש:Hexagone59/אפקט יארקובסקי-או'קיפי-ראדזייבסקי-פאדאק

מתוך ויקיפדיה, האנציקלופדיה החופשית

450px|thumb|Схема действия YORP-эффекта на астероид асимметричной формы.

450px|thumb|Под действием YORP-эффект меняется скорость и наклон оси вращения, эффект Ярковского вызывает изменение большой полуоси орбиты астероида.


In astronomia, l'effetto YORP, o per esteso effetto Yarkovsky–O'Keefe–Radzievskii–Paddack, è un ampliamento del più noto effetto Yarkovsky per includere anche altri fattori, oltre all'irraggiamento del calore assorbito dal sole, che influiscono sulla variazione della velocità di rotazione dei corpi di piccole dimensioni del sistema solare.

Origine del termine[עריכת קוד מקור | עריכה]

Il termine è stato utilizzato per la prima volta dal geofisico statunitense David Perry Rubincam nel 2000 per indicare collettivamente alcuni fattori che si era ipotizzato, e in parte verificato, influire sulla velocità di rotazione degli asteroidi.

Storia[עריכת קוד מקור | עריכה]

Già nel XIX secolo Ivan Osipovič Jarkovskij aveva ipotizzato che il differente gradiente di emissione di radiazione infrarossa, conseguenza del diverso tempo di esposizione della superficie in rotazione, potesse determinare un momento angolare capace di variare la velocità di rotazione del corpo celeste. Espressa con i termini della fisica quantistica si può asserire che ogni fotone riemesso sottrae un momento [1]. Questa ipotesi, nota come effetto Yarkovsky, è stata dimostrata misurandone gli effetti sull'asteroide 6489 Golevka nell'arco di una dozzina di anni.

Nel XX secolo Vladimir Vyačeslavovič Radzievskij ipotizzò una variazione del momento angolare indotta dal diverso grado di albedo delle varie parti della superficie mentre Stephen Paddack e John O'Keefe ipotizzarono una variazione indotta dall'irregolarità della forma.

Conferme attuali[עריכת קוד מקור | עריכה]

La conferma dell'esistenza dell'effetto YORP è arrivata da vari studi condotti nel 2007 su due piccoli asteroidi, (תבנית:DP e 1862 Apollo), il primo dei quali è stato poi ribattezzato 54509 YORP per celebrare il positivo risultato ottenuto.

Dalle misure effettuate 54509 YORP raddoppierà la propria velocità di rotazione in circa 600.000 anni per poi raggiungere in 35 milioni di anni i 20 secondi al giro che si ritiene sia la velocità critica che causerà cambiamenti morfologici nell'asteroide, compresa un'eventuale rottura che originerebbe un sistema binario. 54509 YORP ha anche subito nel periodo di osservazione una variazione dell'asse di rotazione e dell'angolo di precessione.

Ulteriori osservazioni[עריכת קוד מקור | עריכה]

Le osservazioni mostrano che gli asteroidi di dimensione superiore ai 125 km hanno una curva di distribuzione delle velocità di rotazione di tipo maxwelliano, mentre alle dimensioni inferiori si ha una polarizzazione verso le velocità estremamente basse o estremamente alte. Si ritiene che l'effetto YORP sia la causa di questo fenomeno.
L'effetto YORP offre anche una spiegazione più semplice per la scarsità di oggetti celesti asimmetrici di piccole dimensioni[2] e per l'esistenza di asteroidi binari, che non potrebbero essere unicamente giustificati come risultanza di eventi d'impatto tra asteroidi, data la probabilità estremamente bassa che questi si verifichino con condizioni di velocità e angolo d'impatto adeguati.[3]


אפקט יורפ או אפקט יארקובסקי-או'קיפי-ראדזייבסקי-פאדאק ( באנגלית: YORP Effect ) הינה תופעה המסבירה שינויים בסיבוב העצמי של אסטרואידים קטנים יחסית כתוצאה מהתנע של הפוטונים הניתכים עליהם מהשמש. האפקט משנה את מורפולגיית האסטרואיד ועשוי לגרום בסופו של דבר להעלמותו ממערכת השמש.


הוא חלש פי 100 יחסית לאפקט יארקובסקי שבזכותו הוא התגלה אך שמשפיע פחות על התנע הזוויתי. האפקט משפיע באופן שונה על פני שטח שונים והרכב גאולוגי שונה: הוא אפסי על מסלול אליפטי או על גוף מוליך חשמלי.


In the 19th century, Ivan 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 idea to rotation based on changes in albedo[1] 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 objects.[2]

Histoire et origine[עריכת קוד מקור | עריכה]

L'effet YORP est une conséquence de la radiation anisotrope d'un corps en mouvement chauffé par le Soleil.

Au תבנית:XIXe siècle, Ivan Yarkovsky remarqua que la radiation infrarouge émise par un corps chauffé par le Soleil emportait une partie de la quantité de mouvement de celui-ci, affectant en fin de compte le mouvement de l'objet.

En termes modernes, on montre en mécanique quantique que tout photon transporte une quantité de mouvement :

avec E = hν son énergie et c la vitesse de la lumière. Selon la manière dont ce photon est émis, il peut résulter de cette interaction une force et un couple sur l'objet et, à très long terme, modifier complètement sa trajectoire. Cette force est responsable de l'effet Yarkovsky, et domine en général largement l'effet du couple. Ce dernier, d'ordre 2, se révèle par ailleurs bien plus difficile à étudier.

Radzievskii utilisa cette idée sur un corps en rotation, faisant varier l'albédo de celui-ci[4]. Paddack et תבנית:Lien ont mis en avant le rôle principal de la géométrie de l'objet dans l'intensité de cet effet[5]. Paddack et Rhee ont suggéré que cet effet pouvait expliquer la rareté des petites particules asymétriques dans le système solaire, qui auraient ainsi été éjectées[6].

Le nom de l'effet fut proposé par David Rubincam en 2000[7].

Observations[עריכת קוד מקור | עריכה]

Début mars 2007, une observation directe de l'effet YORP sur les petits astéroïdes (54509) YORP[8][9] et Apollo[10][11] a confirmé les prédictions faites a priori[12][13]. La vitesse de rotation de (54509) YORP sera doublée d'ici 600 000 ans, et son axe de rotation comme sa période de précession sont affectés. La conséquence à long terme est la mise en résonance des astéroïdes, ce qui pourrait expliquer l'existence d'astéroïdes binaires[14].

On observe pour les astéroïdes de 125 km de diamètre et plus une distribution de Maxwell-Boltzmann des vitesses de rotation, alors qu'une majorité des astéroïdes plus petits (entre 50 km et 125 km de diamètre) présentent une vitesse de rotation élevée. Les plus petits astéroïdes montrent un excès marqué de corps en rotation très lente et de corps en rotation très rapide, une observation encore plus frappante quand on considère de petits objets. Ces résultats appuient l'idée qu'un ou plusieurs mécanismes dépendant de la taille des astéroïdes les prive des vitesses de rotation intermédiaires. L'effet YORP est pressenti comme la meilleure explication concernant les plus petits objets ; néanmoins, il n'est pas suffisant pour influencer la rotation des astéroïdes plus grands tels que (253) Mathilde, qui montre pourtant les mêmes modifications.

Voir aussi[עריכת קוד מקור | עריכה]

Liens externes[עריכת קוד מקור | עריכה]


אנגלית[עריכת קוד מקור | עריכה]

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

In the 19th century, Ivan 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 (= תבנית:Italics correctionν) is its energy and c is the speed of light. Radzievskii applied the idea to rotation based on changes in albedo[15] 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 objects.[16]

Observations[עריכת קוד מקור | עריכה]

In 2007 there was direct observational confirmation of the YORP effect on the small asteroids 54509 YORP (then designated תבנית:Mpl)[17][18] and 1862 Apollo.[19] 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.[20]

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, so a different explanation must be sought for objects such as 253 Mathilde.

In late 2013 asteroid P/2013 R3 was observed breaking apart, perhaps because of the YORP effect.[21]

Example[עריכת קוד מקור | עריכה]

Assume a rotating spherical asteroid has two wedges attached to its equator.תבנית:What 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 תבנית:Mp was later named 54509 YORP to honor its part in the confirmation of this phenomenon.

See also[עריכת קוד מקור | עריכה]

References[עריכת קוד מקור | עריכה]

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

Further reading[עריכת קוד מקור | עריכה]

External links[עריכת קוד מקור | עריכה]



דוגמה אחרת מגרמנית - אבק אינטרא-פלנטארי

Ähnliches[עריכת קוד מקור | עריכה]

Staubpartikel, die asymmetrisch geformt sind, können ebenfalls durch Lichteinfall in Luft in Rotation geraten. Manche Teilchen können dabei eine Form haben, dass die nach dem Licht orientierte Rotation eine gerichtete Bewegung in Luft bewirkt. Diese Photophorese trägt zwar nur einen sehr geringen Anteil von Staubteilchen nach oben, wirkt aber bedeutsam der Absetzbewegung durch die Schwerkraft entgegen und hilft das Vorhandensein von Staubteilchen und Mikroorganisman bis hinauf in die Stratosphäre zu erklären. Publikationen zu Photophorese gibt es zumindest seit 1932, der Linzer Experimentalphysiker Hans Rohatschek hat zwischen 1955 und 1984 dazu veröffentlicht.[22] (http://link.springer.com/article/10.1007%2FBF00053801)

PDF:

http://www.lpi.usra.edu/meetings/lpsc2007/pdf/2438.pdf -- DIRECT DETECTION OF THE ASTEROIDAL YORP EFFECT


בדוק:

https://es.wikipedia.org/wiki/Efecto_YORP

https://ru.wikipedia.org/wiki/YORP-%D1%8D%D1%84%D1%84%D0%B5%D0%BA%D1%82 https://sl.wikipedia.org/wiki/Pojav_JORP


קישורים חיצוניים=[עריכת קוד מקור | עריכה]

הערות שוליים[עריכת קוד מקור | עריכה]

  1. ^ Dove: è la costante di Planck, è la frequenza a cui è emesso il fotone, è la velocità della luce.
  2. ^ {{en}} S.J. Paddack, J. W. Rhee, Geophys. Res. Lett 2, 365 (1975).
  3. ^ {{en}} D.P. Rubincam, S. J. Paddack, Science 316 211 (2007).
  4. ^ {{en}}/{{ru}} V.V. Radzievskii : « A mechanism for the disintegration of asteroids and meteorites », Dokl. Akad. Nauk SSSR (1954).
  5. ^ {{en}} John O'Keefe : « Tektites and Their Origin », Elsevier, Amsterdam (1976).
  6. ^ {{en}} S.J. Paddack, J. W. Rhee, Geophys. Res. Lett 2, 365 (1975).
  7. ^ David Rubincam : « Radiative spin-up and spin-down of small asteroids », Icarus (2000).
  8. ^ {{en}} S. C. Lowry et. al. Science 316 272 (2007) (introduction).
  9. ^ {{en}} P.A. Taylor et. al. Science 316 274 (2007) (introduction).
  10. ^ {{en}} M. Kaasalenien et. al. Nature 446, 420 (2007).
  11. ^ <nowiki>{{en}}</nowiki> New Scientist Space : « Sun sends bumpy asteroids into a spin »
  12. ^ {{en}} Discovery News : « Asteroid Spin Changed by Sunlight ».
  13. ^ {{de}} Berliner Zeitung : « Die Strahlung der Sonne versetzt kleine Himmelskörper ganz langsam in Schwung ».
  14. ^ {{en}} D.P. Rubincam, S. J. Paddack, Science 316 211 (2007).
  15. ^ Radzievskii (1954)
  16. ^ S. J. Paddack, J. W. Rhee, Geophys. Res. Lett 2, 365 (1975)
  17. ^ Lowry, S. C.; Fitzsimmons, A.; Pravec, P.; Vokrouhlicky, D.; Boehnhardt, H.; Taylor, P. A.; Margot, J.-L.; Galad, A.; Irwin, M.; Irwin, J.; Kusnirak, P. (2007). "Direct Detection of the Asteroidal YORP Effect". Science. 316 (5822): 272–274. Bibcode:2007Sci...316..272L. doi:10.1126/science.1139040. ISSN 0036-8075. PMID 17347414.
  18. ^ Taylor, P. A.; Margot, J.-L.; Vokrouhlicky, D.; Scheeres, D. J.; Pravec, P.; Lowry, S. C.; Fitzsimmons, A.; Nolan, M. C.; Ostro, S. J.; Benner, L. A. M.; Giorgini, J. D.; Magri, C. (2007). "Spin Rate of Asteroid (54509) 2000 PH5 Increasing Due to the YORP Effect". Science. 316 (5822): 274–277. Bibcode:2007Sci...316..274T. doi:10.1126/science.1139038. ISSN 0036-8075.
  19. ^ Kaasalainen, Mikko; Ďurech, Josef; Warner, Brian D.; Krugly, Yurij N.; Gaftonyuk, Ninel M. (2007). "Acceleration of the rotation of asteroid 1862 Apollo by radiation torques". Nature. 446 (7134): 420. Bibcode:2007Natur.446..420K. doi:10.1038/nature05614.
  20. ^ Rubincam, D. P.; Paddack, S. J. (2007). "As Tiny Worlds Turn". Science. 316 (5822): 211. doi:10.1126/science.1141930.
  21. ^ "Hubble witnesses an asteroid mysteriously disintegrating".
  22. ^ Hans Rohatschek, Johannes Kepler University Linz, The Role of Gravitophotophoresis for Stratospheric and Mesospheric Particulates, in: Journal of Atmospheric Chemistry 1, (1984) S.377-389, vom 7. Oktober 1983, Revision 16. Jänner 1984 Print, online abgerufen am 9. Februar 2014
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